JPH11164321A - Image decoding method, image decoder and data storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a reproduced image for a long time even for a portable terminal by decoding a compression coded image signal while suppressing power consumption. SOLUTION: A controller 105 discriminates whether a display mode is a color display mode or a monochromatic display mode. In the color display mode, coded data of a luminance signal and coded data of a color difference signal are fed to an information source decoding section 100b by changeover control of a switch 106 of the controller 105. In the monochromatic display mode, the coded data of the color difference signal are aborted and only the coding data of the luminance signal are fed to the information source decoding section 100b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an image decoding method,
The present invention relates to an image decoding device and a data storage medium, and more particularly to power saving in a monochrome display mode in a digital image decoding process.

[0002]

2. Description of the Related Art In order to efficiently store or transmit digital image information, it is necessary to compress and encode digital image information. At present, as a method for compressing and encoding digital image information, JPEG (Joint Photographic) is used. Co
ding Experts Group) and MPEG (Moving Picture Expe
In addition to discrete cosine transform (DCT) represented by rts Group), there is a waveform coding method such as subband, wavelet, and fractal.

As a method of removing redundant image information between display screens such as adjacent frames, inter prediction using motion compensation is performed, that is, the pixel values of the pixels of the current screen are compared with the pixel values of the previous screen. There is a method of expressing the difference signal by using a difference from the pixel value of the pixel and performing waveform coding on the difference signal.

[0004] As a conventional image processing method, an image coding method and an image decoding method of the MPEG system in which DCT processing with motion compensation is performed will be briefly described. In this image encoding method, first, an input image signal is
The image signal is divided into a plurality of image signals corresponding to a plurality of blocks (macroblocks) constituting one display screen, and encoding processing of the image signal corresponding to each macroblock is performed for each macroblock. Here, one macro block corresponds to the above 1
It corresponds to an image display area of 16 × 16 pixels on the display screen.

More specifically, an image signal corresponding to each macroblock is divided into subblocks corresponding to an image display area consisting of 8 × 8 pixels, and a DCT is applied to the image signal corresponding to each subblock. Processing is performed to generate DCT coefficients corresponding to each sub-block. Then, the DCT coefficient corresponding to each sub-block is quantized to generate a quantized value corresponding to each sub-block. A method of coding an image signal corresponding to a sub-block by DCT processing and quantization processing in this way is called an intra-frame coding method. On the receiving side, an inverse quantization process and an inverse DCT process are performed on the quantized value corresponding to each of the sub-blocks, and an image signal corresponding to each macro block is reproduced.

On the other hand, there is an image signal encoding method called an inter-frame encoding method. In this encoding method, first, a method of detecting the motion of an image on a display screen, such as block matching, is used to detect another frame screen temporally adjacent to the frame screen to be encoded. From among them, a macroblock having the smallest pixel value error compared to the target macroblock to be encoded is detected as a predicted macroblock.

Subsequently, based on the motion of the image detected at this time, motion compensation is performed on the image signal of the frame screen which has already been subjected to the encoding process, and the optimum value is obtained as the predicted value of the image signal of the target macroblock. Obtain an image signal. Here, a signal indicating a macroblock (prediction macroblock) having the smallest error of the image signal with respect to the target macroblock is a motion vector. Note that a frame screen including the above-described predicted macroblock, which is referred to to generate a predicted value of the image signal of the target macroblock, is hereinafter referred to as a reference frame screen.

Next, a difference signal between the image signal of the sub-block constituting the target macroblock and its predicted value is obtained, a DCT process is performed on the difference signal to generate a DCT coefficient, and a quantization process is performed on the DCT coefficient. To generate a quantized value. Then, the quantization values of all the sub-blocks constituting the target macroblock are transmitted or stored together with the motion information.

On the receiving side, the quantization value (quantized DCT coefficient) is sequentially subjected to inverse quantization and inverse DCT to restore a difference signal corresponding to each macroblock. The image signal of the decoded reference frame screen is motion-compensated with a motion vector,
A predicted value of an image signal corresponding to a target macroblock to be decoded is generated, and the predicted value and the difference signal are added to reproduce an image signal of the target macroblock.

In such MPEG image processing,
When performing the compression encoding process of the luminance signal and the chrominance signal constituting the image signal on the transmission side, the intra-frame encoding process and the inter-frame encoding process are appropriately switched on a macroblock basis, and are performed. On the receiving side, the intra-frame decoding process or the inter-frame decoding process is appropriately performed for each macroblock on the luminance signal and the chrominance signal composing the digital image signal, which have been compression-encoded on the transmission side, so that the original By reproducing the luminance signal and the color difference signal, the digital image signal can be displayed as a color image.

In particular, in the above-mentioned MPEG system, the encoding process of an image signal is performed using a macroblock consisting of four luminance blocks 701 to 704 and two color difference blocks 705 and 706 shown in FIG. The image signal thus encoded is transmitted by satellite broadcasting or cable transmission, and is reproduced by a stationary receiver or a portable receiver.

[0012]

In the process of reproducing an image signal by a portable receiver, it is required to save power, that is, to reduce the power consumed for signal processing. Specifically, when an image signal is reproduced and displayed as a color image, the encoded luminance signal and chrominance signal constituting the image signal are decoded, and at this time, for the inter-frame encoded image signal, It is necessary to obtain not only the predicted value of the luminance signal but also the predicted value of the color difference signal, and the amount of signal processing for obtaining the predicted value of the image signal is large, and the amount of power required for this processing is necessarily large. Becomes

When a color signal is displayed, the reproduced luminance signal Y and color difference signals U and V must be converted into RGB signals based on the following equations (1) to (3). . R = 1.164 (Y-16) +1.596 (U-128) (1) G = 1.164 (Y-16) -0.813 (U-128) -0.391 (V-128) .. (2) B = 1.164 (Y−16) +2.018 (V−128) (3) However, it is necessary to perform a predetermined multiplication process on the color difference signals U and V when performing the conversion. This multiplication process consumes considerable power. As a result, it is difficult for the portable terminal device to reproduce and display the image signal processed by the MPEG method or the like as a color image with power saving, and there is a problem that the reproduced image cannot be viewed for a long time. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can decode a compression-encoded image signal while suppressing power consumption. An image decoding method and an image decoding device that enable display of a long-time reproduced image, and
It is an object of the present invention to obtain a data recording medium on which an image processing program for realizing a decoding process by the image decoding method is recorded.

[0015]

An image decoding method according to the present invention (claim 1) performs a decoding process on compressed coded data including coded data obtained by coding a luminance signal and a chrominance signal. A digital image decoding method for reproducing an image signal for performing image display, wherein in a color display mode in which an image is displayed in color, both the encoded data of the luminance signal and the encoded data of the color difference signal are both used. In the monochrome display mode in which the image is decoded and the image is displayed in monochrome, only the encoded data of the luminance signal is decoded.

In the image decoding method according to the present invention (claim 2), an image is displayed by performing a decoding process on compressed coded data including coded data obtained by coding a luminance signal and a chrominance signal. A digital image decoding method for reproducing an image signal for decoding, including a decoding process of decoding the coded compressed coded data, and a decoding process of decoding the decoded compressed coded data, In the color display mode in which color display is performed, both the decoded encoded data of the luminance signal and the data of the color difference signal are decoded, and in the monochrome display mode in which an image is displayed in monochrome, the color difference signal The coded data is detected and discarded, and only the coded data of the luminance signal is decoded by the decoding process.

According to a third aspect of the present invention, in the image decoding method according to the second aspect, the coded compressed coded data corresponds to a plurality of transform coefficients obtained by frequency-converting the luminance signal. And a code corresponding to a plurality of transform coefficients obtained by frequency-converting the color difference signal,
According to the unit processing area of a certain size on the display screen,
In the decoding process in the monochrome display mode, a code corresponding to the final conversion coefficient of the luminance signal corresponding to the unit processing area and a code corresponding to the final conversion coefficient of the chrominance signal are detected. Then, all the conversion coefficients from the code corresponding to the first conversion coefficient of the color difference signal arranged next to the code corresponding to the final conversion coefficient of the luminance signal to the code corresponding to the final conversion coefficient of the color difference signal are obtained. The corresponding code is discarded.

According to a fourth aspect of the present invention, in the image decoding method according to the third aspect, the detection of the code corresponding to each of the final transform coefficients is performed immediately after the code corresponding to the final transform coefficient in the bit string. This is performed based on the index data indicating that the immediately preceding code arranged is the code corresponding to the final transform coefficient.

According to a fifth aspect of the present invention, in the image decoding method of the third aspect, a code corresponding to each of the transform coefficients is an identification bit indicating whether the transform coefficient is the final transform coefficient. Is included.

In the image decoding method according to the present invention (claim 6), a difference value between each signal and its predicted value is generated from a luminance signal and a chrominance signal for each unit processing area on a display screen. A decoding process is performed on the compression-encoded data including a transform coefficient obtained by frequency-converting a difference value corresponding to the signal and a motion vector generated in accordance with generation of a predicted value of the luminance signal, and image display is performed. Image decoding method for reproducing an image signal for reproducing the image signal in a color display mode in which an image is displayed in color, wherein the conversion coefficients corresponding to the luminance signal and the color difference signal are restored to a luminance difference value and a color difference difference value, respectively. Difference value restoration processing, a luminance signal reproduction processing for obtaining a prediction value of a luminance signal using the motion vector, and reproducing the luminance signal by adding the prediction value and the luminance difference value, corresponding to the luminance signal And a scaling process for converting the scale of the color vector into one corresponding to the chrominance signal, and a predicted value of the chrominance signal is obtained by using the scaled motion vector, and the chrominance is calculated by adding the predicted value and the chrominance difference value. In a monochrome display mode in which a color difference signal reproduction process for reproducing a signal is performed and an image is displayed in monochrome, instead of each process in the color display mode, a difference value for restoring a conversion coefficient corresponding to the luminance signal to a luminance difference value A restoration process and a reproduction process of obtaining a predicted value of a luminance signal using the motion vector and adding the predicted value and the luminance difference value to reproduce a luminance signal are performed.

An image decoding apparatus according to the present invention (claim 7) performs a decoding process on compressed coded data including coded data obtained by coding a luminance signal and a chrominance signal to display an image. A digital image decoding apparatus that reproduces an image signal, wherein a mode determining unit determines which of a color display mode in which images are displayed in color and a monochrome display mode in which images are displayed in monochrome is set. And outputs the encoded data of the luminance signal and the encoded data of the color difference signal in the color display mode, and outputs the encoded data of the luminance signal in the monochrome display mode. Data selecting means for discarding the encoded data of the color difference signal, and a decoder for decoding the encoded data output from the data selecting means It is those with a.

According to the present invention (claim 8), in the image decoding device according to claim 7, a plurality of compression-encoded data obtained by performing an encoding process including frequency conversion on the luminance signal is obtained. A data decoder that decodes the bit sequence into a coded bit sequence including a luminance conversion coefficient and a plurality of color difference conversion coefficients obtained by performing an encoding process including frequency conversion on the color difference signal; In the color display mode, the luminance conversion coefficient and the chrominance conversion coefficient obtained by decoding the bit string are output. In the monochrome display mode, the chrominance conversion coefficient among the conversion coefficients obtained by decoding the bit string is discarded. And outputs only the luminance conversion coefficient, and the decoder decodes the conversion coefficient output from the data selection means, including inverse frequency conversion processing. It is obtained by a configuration for decoding a sense.

An image decoding apparatus according to the present invention (claim 9) generates a difference value between each signal and its predicted value from a luminance signal and a chrominance signal for each unit processing area on a display screen. A decoding process is performed on the coded compression-encoded data including the transform coefficient obtained by frequency-converting the difference value corresponding to the signal and the motion vector generated with the generation of the predicted value of the luminance signal, A digital image decoding device for reproducing an image signal for performing image display, comprising: a frame memory for storing reproduced luminance reproduction signals and color difference reproduction signals; a color display mode for displaying images in color; A mode determining means for determining which of the monochrome display modes of the monochrome display mode is set; and decoding the coded compression-encoded data to obtain the luminance signal and the color difference. And a data decoder that outputs a conversion coefficient corresponding to the signal and the motion vector, and receives an output of the mode determination unit, and in the color display mode, outputs conversion coefficients of the luminance signal and the color difference signal, and outputs the monochrome display. In the mode, a data selection unit that discards the conversion coefficient of the color difference signal and outputs only the conversion coefficient of the luminance signal,
A decoder for performing a decoding process including an inverse frequency conversion process on the transform coefficient output from the data selection unit to generate a difference value of a luminance signal or a chrominance signal, and receiving an output of the mode determination unit, In the color display mode, a scaling process is performed to obtain a predicted value of a luminance signal from the frame memory using the motion vector, and to convert a scale of a motion vector corresponding to the luminance signal to a value corresponding to the color difference signal. Obtaining a predicted value of a color difference signal from the frame memory using the scaled motion vector, and obtaining a predicted value of a luminance signal from the frame memory using the motion vector in the monochrome display mode. And the addition of the difference value of the luminance signal and the predicted value of the luminance signal or the difference value of the color difference signal and the By adding the prediction value of the difference signal and generates a luminance reproduction signal or a color difference reproduction signals simultaneously,
An adder for storing the luminance reproduction signal and the color difference reproduction signal in the frame memory.

According to a tenth aspect of the present invention, there is provided a data storage medium, as an image processing program, for causing a computer to perform image processing by the image decoding method according to any one of the first to sixth aspects. Is stored.

[0025]

The embodiments of the present invention will be described below. FIG. 1 is a block diagram illustrating a digital image decoding apparatus according to an embodiment of the present invention. In the figure, reference numeral 100 denotes an image decoding apparatus that decodes compressed and encoded data of a digital image signal and reproduces the image signal. The reproduced output is displayed as an image on a display device (not shown).

The image decoding apparatus 100 receives a bit stream 200 including encoded data of a luminance signal and a chrominance signal constituting an image signal, and performs variable length decoding on the bit stream 200 to form an intra macroblock or an inter macroblock. And a variable length decoding unit 100a that outputs control data together with quantization values corresponding to the luminance block and the chrominance block to be processed, and the motion vector of each inter macro block. Here, the intra macroblock is obtained by performing the above-described intra-frame coding process on the corresponding image signal, and the inter-macroblock is obtained by performing the above-described interframe coding process on the corresponding image signal. It is.

The image decoding apparatus 100 further includes an information source decoding unit 100b that performs an information source decoding process on the quantized value using the motion vector as necessary.
A controller 105 that controls the variable length decoding unit 100a and the information source decoding unit 100b based on the display mode signal 123 supplied from outside the apparatus and the control data output from the variable length decoding unit 100a. And The display mode signal 12 supplied to the controller 105
Numeral 3 indicates whether the display mode of the decoded image signal is the monochrome display mode or the color display mode. Here, the display mode signal 123 is set by the user. . However, the present image decoding apparatus is configured to include a generator of the display mode signal 123, and the generator is configured to operate the display mode signal 123 when the power supply voltage supplied to the present image decoding apparatus 100 falls below a certain level. The signal may automatically be switched from the signal indicating the color display mode to the signal indicating the monochrome display mode.

The variable-length decoding unit 100a generates a code (data of each bit) in the bit stream 200.
Has a data storage area capable of storing a predetermined number of bits, for example, 16 or 32 bits, outputs a stored code string, and shifts the code of the bit stream 200 by the number of bits based on the shift control signal 125. It has a shifter 102. The variable-length decoding unit 100a decodes the code string (that is, code) output from the shifter 102, outputs data corresponding to the decoded code, and outputs only data corresponding to the number of bits corresponding to the decoded code. Code decoder 103 for outputting the shift control signal 125 for performing the shift by the shifter
And a changeover switch 106 for switching, based on a control signal 140a from the controller 105, whether to output the data output from the code decoder 103 to the information source decoding unit 100b or discard the data.

Here, the code decoder 103 includes a code table storing data such as codes and corresponding quantization values, motion vectors, or control values, and a code string input to the decoder 103. It has a matching circuit for comparing the included code with the code in the code table, and outputs data corresponding to the stored code matched with the input code.

The information source decoding unit 100b inversely quantizes the quantized value, which is output data from the variable length decoding unit 100a, for each sub-block constituting a macroblock, and An inverse quantizer 109 for reproducing a DCT coefficient to be converted, and an inverse DT for applying an inverse DCT process to the reproduced DCT coefficient for each sub-block and outputting an image signal or a difference signal corresponding to each sub-block.
It has a CT unit 110.

The information source decoding unit 100b calculates a predicted value of an image signal corresponding to a target inter macroblock to be decoded based on the decoded image signal 137 and the motion vector 128. A predicted value generation unit 100b1 that generates the predicted value and the inverse DCT unit 11
Adder 111 for adding the difference signal output from 0
And a switch 150 connected between the adder 111 and the predicted value generation unit 100b1 to turn on and off the supply of the predicted value to the adder 111 by a control signal 140d from the controller 105. The image signal output from the inverse DCT unit 110 is output as an image signal corresponding to an intra macroblock, and the added value 137 of the difference signal and the prediction value is output as an image signal corresponding to an inter macroblock. Has become.

Here, the predicted value generation unit 100b1
A frame memory 113 for temporarily storing the decoded image signal for one frame or a predetermined number of frames.
And a first address generator 112 that receives the motion vector 128 output from the variable length decoding unit 100a and generates an address of the frame memory 113. The predicted value generation unit 100b1 is a motion vector scaling unit 1 that scales a motion vector corresponding to the luminance block so as to correspond to a chrominance block.
14, a second address generator 115 for generating an address of the frame memory 113 based on the scaled motion vector, and a scaling unit 11
4 and a switch 116 provided between the variable length decoding unit 100a and controlled to open and close by a control signal 140b from the controller 105, and one of the outputs of the first and second address generators 112 and 115. Is selected based on a control signal 140c from the controller 105 and supplied to the frame memory 113.

The image decoding apparatus 100 according to the present embodiment having such a configuration, as the compression encoded data, encodes the intra-frame encoded data generated by the intra-frame encoding of the digital image signal and the digital image signal. A bit stream including inter-frame encoded data generated by inter-frame encoding is input.

Next, the data structure of the bit stream 200 input to the image decoding apparatus 100 and the contents of the encoding process for generating the bit stream 200 will be briefly described.

In the intra-frame encoding process, an image signal composed of a luminance signal and a chrominance signal is divided so as to correspond to the macroblock, and the divided image signal is compression-coded in macroblock units. Specifically, an image signal corresponding to the macroblock is converted into a discrete cosine transform (DC) for each subblock constituting the macroblock.
T) is converted into a frequency coefficient. Here, as shown in FIG. 7, four sub-blocks constituting the macroblock correspond to a luminance signal composed of 8 × 8 samples.
Two luminance blocks 701 to 704 and two color difference blocks 705 corresponding to a color difference signal composed of 8 × 8 samples.
706 is used. Then, the frequency coefficient corresponding to each of the sub-blocks is quantized by a predetermined quantization width to generate a quantized value, and the quantized value is subjected to variable-length coding to generate coded data corresponding to a macroblock.

In the above-mentioned inter-frame encoding processing, a prediction is performed by using the correlation between the image frames to minimize the difference value between the image signal of the target macro block to be encoded in the motion compensation mode. Detecting a macroblock, converting a difference value of an image signal between the predicted macroblock and the target macroblock into a frequency coefficient by DCT processing,
Further, the frequency coefficient is converted into a quantization value by a quantization process. Then, the quantization value corresponding to the target macroblock and the motion vector are variable-length coded and multiplexed to generate coded data corresponding to the macroblock.

FIG. 2 shows a data structure of a bit stream 200 including the above-mentioned intra-coded data and inter-coded data. This bit stream 200
Sets the start position of the image signal corresponding to one display screen to 3
Synchronization signal (PS) indicated by a unique 2-bit code
C) 201, PTYPE data 202 indicating by a 2-bit code whether the encoding process on the image signal is an intra-frame encoding process or an inter-frame encoding process.
232, and quantization width data 203, 23 indicating the quantization width in the quantization process at the time of encoding by a 5-bit code.
3 and each macro block M (i), M (i + 1),.
, M (j), data D (i), D (i + 1),..., D (j), D (j +) corresponding to M (j + 1),.
1),... Here, the PTYPE
The data 202 is obtained by performing the intra-frame encoding process on the PTYP
E data 232 indicates an inter-frame encoding process,
The macroblocks M (i) and M (i + 1) are intra macroblocks in which the corresponding image signals have been subjected to intra-frame encoding processing.
(J) and M (j + 1) are inter-macroblocks in which the corresponding image signal has been subjected to inter-frame encoding processing.

The above intra macroblocks M (i), M
Data D (i) and D (i + 1) corresponding to (i + 1)
Is a 6-bit code, and CBP data 204, 21 indicating whether or not a DCT coefficient exists corresponding to each sub-block constituting a macroblock by each bit.
7, the DCT coefficient group corresponding to each sub-block and
Block information 20a1 to 20a6, 20b1-2 including EOB data indicating the final DCT coefficient in the CT coefficient group
0b4. Here, the CBP data 20
4, 217, the code corresponding to the sub-block in which the DCT coefficient exists is “1”, and the code corresponding to the sub-block in which the DCT coefficient does not exist is “0”. further,
Block information 20a1-20a of each of the above sub-blocks
6, 20b1 to 20b4 are DCT coefficient groups 21
a1 to 21a6, 21b1 to 21b4, and EOB data 22a1 to 22a6, 22b1 to 22b4.

The above inter macro blocks M (j), M
Data D (j) and D (j + 1) corresponding to (j + 1)
Are the motion vectors 234 and 248 that have been
And CBP data 235, 24 indicating whether or not a DCT coefficient exists corresponding to each sub-block constituting a macro block by each bit.
9, the DCT coefficient group corresponding to each sub-block and the D
Block information 20c1 to 20c6, 20d1-2 including EOB data indicating the final DCT coefficient in the CT coefficient group
0d4. Here, the CBP data 23
The codes constituting 5,248 are “1” corresponding to the sub-block in which the DCT coefficient exists, and “0” corresponding to the sub-block in which the DCT coefficient does not exist. Further, the block information 20c of each of the above sub-blocks
1 to 20c6, 20d1 to 20d4 are DCT coefficient groups 21c1 to 21c6, 21d1 to 21d4 and EO, respectively.
B data 22c1 to 22c6 and 22d1 to 22d4.

The bit stream 200 has a structure in which data corresponding to each macro block as described above is sequentially arranged up to the data of the last macro block constituting one display screen. Each D shown in FIG.
CT coefficient groups 21a1 to 21a6, 21b1 to 21b4,
Strictly speaking, 21c1 to 21c6 and 21d1 to 21d4 are arranged by arranging codes obtained by performing variable length coding on quantized values corresponding to DCT coefficients by an amount corresponding to a plurality of DCT coefficients corresponding to each sub-block. Things.

Hereinafter, the variable length encoding process will be briefly described with reference to FIG. FIG. 8A shows a DCT obtained by performing DCT processing on an image signal corresponding to a sub-block.
4 shows an arrangement of coefficients in a frequency space. Here, for the sake of simplicity, the sub-block is an image space composed of 4 × 4 pixels.

The frequency space F corresponding to the above sub-block
Then, the first through third coefficients a, b,
c and the third coefficient d from the left in the lower row are non-zero.
, And all other coefficients are 0. Also, quantized values A to D obtained by quantizing the DCT coefficients a to d in the frequency space F (FIG. 8B)
), The variable-length encoding process is performed in the order (scan order) indicated by the dotted arrow S. In this case, the quantized final DCT coefficient becomes the quantized value D.

FIG. 8C shows the quantized DCT.
The coefficients (quantized values) and the codes (codes) obtained by the variable-length coding are shown in association with each other. In the variable-length encoding of the quantized value, the level (level) of the non-zero quantized value and the number of consecutive quantized zeros (runs) located before the non-zero quantized value in the scan order. ) Are converted into one variable-length code based on the variable-length coding table T shown in FIG. 8D. The variable-length coding table T indicates variable-length codes corresponding to the respective events, and the table T also indicates a code “10” corresponding to the EOB data. Although the actual quantization level has positive and negative values, the distinction between the positive and negative quantization levels is not shown here for the sake of simplicity.

For example, the quantization values A to D are respectively
If A = 1, B = 2, C = 1, D = 2, the quantization value A
Forms an event (0, 1). As a result, the quantized value A is converted into a variable-length code "11" based on the table T. Similarly, the quantization values B, C,
D represents events (0,2), (3,1), (1,
2), and the variable-length codes “0100”, “00111”,
Converted to "000110".

Therefore, the encoded bit stream 20
0, the code string corresponding to the DCT coefficient group and the EOB data of the sub-block shown in FIG.
As shown in the table, "... 110100001110001
1010 ... ".

Next, the operation of the image decoding apparatus according to the present embodiment will be described with reference to the operation flow of FIGS. When the bit stream 200 shown in FIG. 2 is input to the input terminal 101 of the image decoding apparatus 100 as encoded data (step 301), in step 302, the input encoded data is converted into a variable-length decoding unit. Decoded at 100a.
That is, the fixed-length code in the bit stream is cut out and converted from a binary number (code) to a numerical value (data).
For the variable length code, a process for checking a code matching the variable length code is performed by referring to the code table, and data corresponding to the code matching the variable length code is output.

More specifically, the input coded data is temporarily stored in the shifter 102 in units of 16 bits or 32 bits, and the stored coded data is supplied to the code decoder 103. In the code decoder 103, the first code in the input coded data is determined by the decoder 1
03 is compared with a plurality of codes in a code table built in the same. Then, from the decryptor 103,
Data corresponding to the code in the code table that matches the above-mentioned first code is output as a first output 124, and bit length data indicating the bit length (CL) of the code is output as a second output 125. When the bit length data is fed back to the shifter 102, the shifter 102
In this case, the input coded data is shifted by the bit length (CL), and the 16-bit or 32-bit coded data stored in the shifter is sent to the code decoder 103 in this state. Further, the above code decoder 1
03 is output as the first output 124.
While being supplied to the controller 105, the controller 10
5 is output to one of the output terminals 107, 108, and 141 of the first switch 106 controlled by the switch 5.

Next, at step 303, the controller 1
05, the output terminal 108 of the first switch 106
It is determined whether the target macroblock to be decoded is an intra macroblock or an inter macroblock based on the PTYPE data supplied as control data from. At this time switch 1
Reference numeral 50 denotes a control signal 140d from the controller 105, which is opened when it is an intra macro block and closed when it is an inter macro block.

In the controller 105, when the target macro block is an intra macro block, the input is made to the input terminal 104 in step 304, and when the target macro block is an inter macro block, in step 504. Based on the mode signal 123, it is determined whether the display mode is the monochrome display mode or the color display mode.

First, the processing when the target macroblock is an intra macroblock will be described with reference to FIGS. If the result of determination in step 304 is that the display mode is not the monochrome display mode, in step 305 the controller 106 causes the switch 106 to output the output of the code decoder 103 to the output terminal 10.
8 is switched. As a result, the encoded data corresponding to the four luminance blocks and the encoded data corresponding to the two chrominance blocks forming the target macroblock are sequentially supplied to the information source decoding unit 100b,
A luminance signal and a color difference signal corresponding to the target macroblock are reproduced. Specifically, the quantized value, which is the encoded data of each block, is converted into a DCT coefficient by an inverse quantizer 109, and a DCT coefficient corresponding to each block is converted into an image corresponding to each block by an inverse DCT unit 110. Converted to a signal.

On the other hand, if the result of determination in step 304 is that the display mode is the monochrome display mode, step 3
In the controller 105, the variable length decoding unit 10
A determination is made as to whether the input data to 0a is encoded data corresponding to the color difference block. As a result, if the input coded data is coded data of a chrominance block, in step 308, the switch 106 is turned on by the control signal 140 a from the controller 105.
03 is controlled so as to be supplied to its output terminal 107, whereby the encoded data corresponding to the chrominance block is discarded. In this case, the DCT coefficients corresponding to the color difference blocks (5) and (6) and the respective EOs
B data is discarded.

If the result of determination in step 306 is that the input coded data is not chrominance blocks but coded data corresponding to a luminance block, in step 307 the switch 106 sets the controller 105
Is controlled so that the output from the decoder 103 is supplied to its output terminal 108, whereby the encoded data corresponding to each of the luminance blocks is supplied to the information source decoding unit 100b, Inverse quantization processing and inverse DCT processing are sequentially performed.

In this way, the image signal of the macro block is reproduced by the decoding process corresponding to each display mode.
Then, in step 309, it is determined whether or not the input coded data is the last coded data. If it is not the last, the processing of steps 301 to 309 is performed. , The encoding process ends.

Next, the processing for discarding the coded data corresponding to the color difference block will be described in detail with reference to FIG. In the controller 105, following the decoded CBP data of the target macroblock, a quantized value corresponding to the DCT coefficient of the first luminance block in the target macroblock is input, and at the same time, the internal counter value k is increased. It is set to 1 (step 402). Subsequent step 403
The controller 105 determines whether or not the counter value k is 4 or less.

As a result, when the counter value k is 4 or less, it is determined that the quantized value input to the information source decoding unit 100b corresponds to the DCT coefficient of the luminance block,
In step 404, k constituting the current macroblock
It is determined whether or not the bit value CBP (k) of the CBP data corresponding to the sub-block is “1”. As a result, if CBP (k) = 0, since there is no DCT coefficient corresponding to the sub-block, step 4
At 06, the counter value k is incremented by one.

On the other hand, if the result of determination in step 404 is that CBP (k) = 1, then in step 405,
DCT coefficient and EO corresponding to the sub-block (k)
The switch 106 is controlled so that the quantized value of the B data is output to the information source decoding unit 100b. Thereafter, at step 406, the counter value k is incremented by one.

If the result of determination in step 403 is that k = 5 or 6, sub-block (k)
Is a color difference block.
A determination is made as to whether P (k) = 1. And
When CBP (k) = 1, the switch 106 is controlled so that the DCT coefficient and the quantized value of the EOB data corresponding to the sub-block (k) are supplied to the ground terminal 107 of the switch 106. As a result, the DCT coefficients of the sub-block (k), which is a color difference block, are discarded. If CBP (k) = 0, there is no DCT coefficient corresponding to the color difference block, and the counter value k is immediately incremented by one at step 406.

Thereafter, at step 409, it is determined whether or not the counter k is equal to or less than 6, and the counter value k is determined.
If the counter value k is equal to or less than 6, the processing of the above steps 403 to 409 is performed. I do. The processing in steps 402 to 409 shown in FIG. 4 is performed in steps 306 to 308 shown in FIG. 3 and step 509 shown in FIG.
To 513.

Next, processing when the target macroblock is an inter macroblock will be described with reference to FIG. If it is determined in step 303 that the target macroblock is an inter macroblock, the controller 105 determines in step 504 whether the display mode is the monochrome display mode.

If the result of the determination is that the display mode is not monochrome display, in step 505, the encoded data corresponding to the luminance block and the chrominance block are decoded, and the difference values of the luminance signals (hereinafter referred to as luminance difference data) are obtained. ) And a color difference signal (hereinafter, also referred to as color difference data). Here, inverse quantization processing and inverse DCT processing are performed on the quantization values corresponding to the difference values of the luminance signal and the color difference signals.

Specifically, in this case, the switch 106 is controlled by the controller 105 so that the input terminal 10
6a is connected to the output terminal 141 so that the motion vector MV can be controlled by the first address generator 112.
Sent to Next, the input terminal 106a of the switch 106 is connected to the output terminal 108, and the CBP data is sent to the controller 105 as the output 126 of the switch 106.
At this time, the quantized value of the DCT coefficient corresponding to the sub-block of the target macroblock is supplied to the inverse quantizer 109 as the output of the switch 106, and the inverse quantizer D
It is converted to CT coefficients. Furthermore, this DCT coefficient is inverse DC
The data is supplied to the T unit 110, where it is restored to luminance difference data and chrominance difference data. Then, the switch 106
When the EOB data is sent to the controller 105 as an output 126 of the CBP, the controller 105
The number of sub-blocks constituting one macro block is calculated using the data. For example, in the case of the macroblock M (j), when the number of sub-blocks becomes six by this calculation, the first switch 106 is controlled so that its input terminal 106a is again connected to the output terminal 141.

Next, in step 506, prediction data of a luminance signal is obtained using the motion vector MV. In the present embodiment, one of the luminance blocks to be subjected to the decoding process
The motion vector MV is added to the coordinates on the display screen,
An address of the frame memory in which the luminance signal of the decoded luminance block is stored is generated, and the luminance signal of the luminance block on the frame memory corresponding to the generated address is used as prediction data.

More specifically, the motion vector MV is output from the first address generator 1 as the output 128 of the switch 106.
12 and is converted into an address of the frame memory 113 by the address generator 112. This conversion is
This is performed by adding a motion vector to the coordinates of the luminance block to be reproduced, and the generated address is sent to the frame memory 113 via the switch 117.

Next, at step 507, the motion vector MV is sent to the motion vector scaling section 114 via the switch 116, where the scaling of the motion vector MV is performed. Here, the value of the motion vector of the scale corresponding to the luminance block is divided by 2 to be the scale corresponding to the color difference block. this is,
This is because each color difference block is composed of pixels obtained by thinning out a plurality of pixels constituting a macroblock so that the number of pixels in each of the vertical direction and the horizontal direction is halved. The motion vector MV obtained by the above scaling is converted into an address on the frame memory 113 by the address generator 115, and
Is sent to the frame memory 113 via which the color difference signal prediction data is obtained.

Thereafter, in step 508, the image signal of the luminance block located at the position indicated by the output address of the address generator 112 is output from the frame memory 113 as luminance prediction data. The luminance signal is reproduced by being added to the luminance difference data. The image signal of the chrominance block at the position indicated by the output address of the address generator 115 is output from the frame memory 113 as chrominance prediction data, and the chrominance prediction data is added to the chrominance difference data by the adder 111. The color difference signal is reproduced.

As described above, the luminance signal and the color difference signal are reproduced and output, and at the same time, the reproduced luminance signal and the color difference signal are referred to at the time of decoding the encoded data corresponding to the next frame. Is stored in the frame memory 113 as an image signal of the reference frame screen.

On the other hand, if the result of determination in step 504 is that the display mode is the monochrome display mode, step 5
At 09, the controller 105 causes the variable-length decoding unit 100a
It is detected whether or not the encoded data output from is the encoded data corresponding to the color difference block. If the output of the variable length decoding 100a is encoded data of a chrominance block, in step 510, the encoded data of the chrominance block is discarded. If the output of the variable-length decoding unit 100a is not coded data of a chrominance block, luminance difference data is generated in step 511, and luminance prediction data is obtained in step 512 using the motion vector MV. Finally, in step 513,
A luminance signal is reproduced by adding the luminance difference data and the luminance prediction data.

That is, when the display mode is the monochrome display mode, the input terminal 106 a of the switch 106 is connected to the output terminal 141, and the motion vector is sent to the address generator 112. Next, the input terminal 10 of the switch 106
6a is connected to the output terminal 108, and the CBP data is sent to the controller 105 as the output 127 of the switch 106a. At this time, the quantized value of the DCT coefficient is sent to the inverse quantizer 109 as the output 126 of the switch 106, and the switch 106 is supplied so that only the quantized value corresponding to the luminance block is supplied to the inverse quantizer 109. Is controlled.

In the controller 105, the CBP data and E
The number of sub-blocks constituting the macro block is calculated based on the OB data. At the start of processing of the first sub-block corresponding to each macroblock, the counter value k
Is set to 0. If the value of the CBP data corresponding to the k-th sub-block is 1 and EOB data exists for this sub-block, and if the CBP data corresponding to the k-th sub-block is 0, The counter value k is incremented by one. When the counter value k is 5 or 6, the processed data is coded data corresponding to the color difference block.
a is connected to the output 107 and the coefficients of the color difference signal are discarded.

The luminance block D thus transmitted
The inverse quantization process and the inverse DCT process are performed only on the quantized value of the CT coefficient, and luminance difference data is generated. At this time, on the other hand, luminance prediction data is generated based on the motion vector, and the adder 111 adds the luminance prediction data and the luminance difference data.

When the display mode is the monochrome display mode as described above, the switch 116 is opened and the scaling of the motion vector is not performed. Switch 1
The seventeen switching terminals 117a are not connected to the input terminal 119. In this way, only the luminance reproduction image is reproduced and output, and is stored in the frame memory 113 at the same time.
Thereafter, in step 514, it is determined whether or not the input coded data is the last coded data. If not, the above steps 301 to 303, 504 are determined.
509 are performed, and if it is the last, the encoding process ends.

As described above, in the present embodiment, in the monochrome display mode, the inverse quantization and inverse DCT processing of the chrominance signal are not performed, and no motion compensation is performed, so that the signal processing amount in the decoding processing can be reduced. Can be. That is, when decoding the digital image signal subjected to the intra-frame encoding process or the inter-frame encoding process and displaying the image,
In the monochrome display mode, the coded data of the chrominance signal is discarded, so that the decoding process for the coded data of the chrominance signal becomes unnecessary.

At the time of decoding, it is necessary to convert the luminance signal (Y) and the color difference signals (U, V) constituting the image signal into RGB signals by the above equations (1) to (3). However, by discarding the color difference signal as described above,
Since only the term including the luminance signal Y remains in the above equation, Y
Calculations for converting a UV signal into an RGB signal can be reduced.

More specifically, in the present embodiment, in the display mode, the amount of calculation for decoding is reduced by ３ by not decoding and reproducing the data of the color difference signals (U, V). Therefore, the power required by the display terminal can be drastically saved, and the image signal can be displayed on the portable terminal for a long time.

Although the above embodiment has been described with reference to the case where DCT transform is used as the encoding process, the present invention relates to a case where encoded data encoded by an encoding method such as wavelet encoding is decoded. In the case of monochrome display, the boundary between the luminance signal data and the chrominance signal data in the bit stream is detected and the chrominance signal data is discarded, so that there is no need to decode the chrominance signal data.

The image signal to be decoded is:
Instead of an image signal corresponding to one display screen, an image signal of an arbitrary shape representing an individual object constituting one display screen may be used. In this case, since the image signal includes a shape signal representing the shape of the object in addition to the brightness signal and the color difference signal of the object, in the monochrome display mode, only the brightness signal and the shape signal are decoded and reproduced. To do.

In the image display using such an arbitrary-shaped image signal, since the synthesis processing of the arbitrary-shaped image signal corresponding to each object is generally performed before the image is displayed, the luminance signal and the shape are output in the monochrome display mode. By decoding and reproducing only the signal, the amount of signal processing for image synthesis can be greatly reduced, and power can be more effectively saved.

In the above embodiment, the final DCT coefficient of the DCT coefficient group is represented by E
Although what is explicitly shown by OB data is shown, instead of using the EOB data, the coded bit stream uses a code corresponding to the quantized DCT coefficient as the last DCT coefficient in the DCT coefficient group. A configuration including an identification bit indicating whether or not the code is the corresponding code may be used.

FIG. 9 shows an encoded bit stream in the case of using a code having such a configuration. This coded bit stream 900 is configured such that each block information in the coded bit stream 200 in the above embodiment does not include EOB data, and a code corresponding to the DCT coefficient in the DCT coefficient group includes the identification bit. It is what it was.

That is, this bit stream 900
Sets the start position of the image signal corresponding to one display screen to 3
Synchronization signal (PS) indicated by a unique 2-bit code
C) 901 and PTYPE data 902 indicating by a 2-bit code whether the encoding process for the image signal is an intra-frame encoding process or an inter-frame encoding process.
932 and quantization width data 903 and 93 indicating the quantization width in the quantization process at the time of encoding by a 5-bit code.
3 and each macro block M (i), M (i + 1),.
, M (j), data D (i), D (i + 1),..., D (j), D (j +) corresponding to M (j + 1),.
1),... Here, the PTYPE
The data 902 is obtained by performing the intra-frame encoding process using the PTYP
E data 932 indicates an inter-frame encoding process,
The macroblocks M (i) and M (i + 1) are intra macroblocks in which the corresponding image signals have been subjected to intra-frame encoding processing.
(J) and M (j + 1) are inter-macroblocks in which the corresponding image signal has been subjected to inter-frame encoding processing.

The above-mentioned intra macro blocks M (i), M
Data D (i) and D (i + 1) corresponding to (i + 1)
Is a 6-bit code, and CBP data 904, 91 indicating whether or not a DCT coefficient exists corresponding to each sub-block constituting a macroblock by each bit.
7 and a DCT coefficient group 91a1 corresponding to each sub-block.
To 91a6, 91b1 to 91b4. Here, the code corresponding to the sub-block in which the DCT coefficient exists is “1”,
The code corresponding to the sub-block having no T coefficient is “0”.

The above-mentioned inter macro blocks M (j), M
Data D (j) and D (j + 1) corresponding to (j + 1)
Are the motion vectors 934 and 948 that have been subjected to variable length coding.
And CBP data 935 and 94 indicating whether or not a DCT coefficient exists corresponding to each sub-block constituting a macroblock by each bit.
9 and a DCT coefficient group 91c1 corresponding to each sub-block.
To 91c6, 91d1 to 91d4. Here, the codes constituting the CBP data 935 and 949 are “1” corresponding to the sub-block where the DCT coefficient exists, and “0” corresponding to the sub-block where the DCT coefficient does not exist. .

The bit stream 900 has a structure in which data corresponding to each macro block as described above is sequentially arranged up to the data of the last macro block constituting one display screen. Each D shown in FIG.
CT coefficient groups 91a1 to 91a6, 91b1 to 91b4
Strictly speaking, 91c1 to 91c6 and 91d1 to 91d4 are arranged by arranging codes obtained by performing variable length coding on quantized values corresponding to DCT coefficients by an amount corresponding to a plurality of DCT coefficients corresponding to each sub-block. Things.

Hereinafter, the variable length encoding process using the code including the identification bits will be briefly described with reference to FIG. FIG. 10A shows a DC signal in a frequency space obtained by performing DCT processing on an image signal corresponding to a sub-block.
FIG. 10B shows the arrangement of T coefficients.
FIG. 10 (a) and FIG. 10 show the order in which the quantized values obtained by the quantization of the coefficients are variable-length coded.
(b) is the same as FIGS. 8 (a) and 8 (b).

FIG. 10 (c) shows the above-mentioned quantized DCT coefficients (quantized values) and the codes (codes) obtained by the variable-length coding in association with each other. In the variable-length encoding of the quantized value, the level (level) of the non-zero quantized value and the number of consecutive quantized values (runs) located before the non-zero quantized value in the scan order are set. ) And an identification bit (last) indicating whether or not the non-zero quantized value is the last to be subjected to variable-length coding among the quantized values corresponding to one sub-block (event). But,
The variable length code is converted into one variable length code based on the variable length coding table Ta shown in FIG. The variable length coding table Ta indicates variable length codes corresponding to the respective events. Further, in the table Ta, the symbol “10” corresponding to the EOB data in the table T shown in FIG. 8D is not shown. Although the actual quantization level has positive and negative values, the distinction between positive and negative quantization is not shown here for simplification of the description.

For example, if the quantization values A to D are A = 1, B = 2, C = 1, and D = 2, the quantization value A is the event (0, 0, 1). As a result, the quantized value A is converted into a variable length code "11" based on the table Ta. Similarly, the quantized values B, C, and D respectively represent events (0, 0,
2), (0, 3, 1) and (1, 1, 2) are formed, and are converted into variable length codes "0100", "00111", and "000100" based on the table Ta, respectively.

Therefore, the encoded bit stream 90
0, the code string of the portion corresponding to the DCT coefficient group of the sub-block shown in FIG. 10 (a) is represented by “... 11010000111000100...
・ ”.

The digital image decoding apparatus which receives the coded bit stream 900 having such a configuration as the input is the code decoder 10 in the digital image decoding apparatus 100.
3 is the first element (identification bit) of the event (last, run, level) obtained by decoding the variable length code
From, the DCT coefficient corresponding to this event is the final DCT
This can be realized by adopting a configuration for detecting whether or not the coefficient is a coefficient.

For example, when the variable length code "000111" in the bit stream is decoded, the last (identification bit) which is the first element of the corresponding event (0, 3, 1) is "0". It can detect that the DCT coefficient corresponding to this event is not the last DCT coefficient among the plurality of DCT coefficients corresponding to one sub-block, while decoding the variable-length code “000100” in the bit stream. In this case, since the last element (identification bit), which is the first element of the corresponding event (1, 1, 2), is “1”, the DCT coefficient corresponding to this event corresponds to one sub-block. Can be detected as the final DCT coefficient among the DCT coefficients. In this way, in this digital image decoding apparatus, decoding by the controller 105 based on the EOB data in the coded bit stream 200 shown in FIG. 2 is performed based on the identification bits included in the variable length code corresponding to the DCT coefficient. The decoding control similar to the decoding control is performed.

Further, a decoding program for realizing the configuration of the digital image decoding method shown in the above-described embodiment is recorded on a data storage medium such as a floppy disk. The illustrated processing can be easily performed by an independent computer system.

FIG. 6 is a diagram for explaining a case where image processing by the digital image decoding method according to the above-described embodiment is executed by a computer system using a floppy disk storing the above-mentioned decoding program.

FIG. 6B shows the external appearance, cross-sectional structure, and floppy disk of the floppy disk viewed from the front, and FIG. 6A shows an example of the physical format of the floppy disk which is the main body of the data storage medium. I have. The floppy disk FD is built in the case F, and a plurality of tracks Tr are formed concentrically from the outer circumference toward the inner circumference on the surface of the disk FD, and each track is divided into 16 sectors Se in an angular direction. Have been. Therefore, in the floppy disk FD storing the program, data as the program is recorded in an area allocated on the floppy disk FD.

FIG. 6C shows a floppy disk F
D shows a configuration for recording and reproducing the program. When recording the program on the floppy disk FD, data as the program is written from the computer system Cs via the floppy disk drive FDD. When the decoding method is constructed in the computer system Cs by the program in the floppy disk FD, the program is read from the floppy disk FD by the floppy disk drive FDD and transferred to the computer system Cs.

In the above description, the description has been made using a floppy disk as a data storage medium. However, the same can be done using an optical disk. The data storage medium is not limited to this, and the present invention can be similarly implemented as long as it can record a program, such as an IC card or a ROM cassette.

[0095]

As described above, the present invention (claims 1, 2 and 2)
According to 3, 4, 5, 7, 8), in the color display mode, the encoded data of the luminance signal and the color difference signal are decoded,
In the monochrome display mode, the coded data of the chrominance signal is detected, the coded data of the detected chrominance signal is discarded, and only the coded data of the luminance signal is decoded. For decrypting encrypted data, R
The amount of arithmetic processing in the process of performing the GB conversion can be reduced by about 1/3, and a remarkable effect that the portable terminal can reproduce and display an image signal for a long time while suppressing power consumption can be obtained.

According to the present invention (claims 6 and 9),
In the color display mode, the frequency coefficient of the luminance signal is restored to luminance difference data, the frequency coefficient of the color difference signal is restored to color difference data, luminance prediction data is obtained using a motion vector, and the luminance prediction data is added to the luminance difference data. In addition, the chrominance prediction data is obtained using the scaled motion vector and added to the chrominance difference data to generate a luminance reproduction signal and a chrominance reproduction signal.
Since the frequency coefficient of the luminance signal is restored to the luminance difference data, the luminance prediction data is obtained using the motion vector, and the luminance prediction data is added to the luminance difference data to generate only the luminance reproduction signal. In the decoding process of the encoded data to be performed, the scaling process of the motion vector, the generation of the prediction data corresponding to the chrominance block, the addition process of the prediction data and the chrominance difference signal, and the like are reduced. The signal processing amount is greatly reduced, and the power consumption is effectively reduced.

According to the data storage medium of the present invention (claim 10), in the monochrome display mode, the process of discarding the coded data of the color difference signal and decoding only the coded data of the luminance signal can be performed. Since the image processing program to be executed by the computer is stored, loading the image processing program into the computer makes it possible to realize a long-time compression-encoded image signal reproduction process by power saving operation. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a digital image decoding device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a structure of compression-encoded data processed by the data image decoding device.

FIG. 3 is a diagram showing a flow of a process of decoding coded data of an intra block in the digital image decoding device of the embodiment.

FIG. 4 is a diagram showing a flow of a process of discarding encoded data corresponding to a color difference block in the digital image decoding device.

FIG. 5 is a diagram showing a flow of a process of decoding encoded data of an inter block in the digital image decoding device of the embodiment.

FIGS. 6 (a), 6 (b) and 6 (c) illustrate a data storage medium for storing a program for realizing a digital image decoding method according to each of the above-described embodiments by a computer system. FIG.

FIG. 7 is a diagram illustrating a unit of encoding processing in compressed encoded data processed by the data image decoding device.

FIG. 8 is a diagram for explaining variable-length encoding processing (compatible with MPEG2) for generating an encoded bit stream according to the embodiment, and specifically illustrates a two-dimensional array of quantized values (FIG.
(a)), the scan order of the quantized value (FIG. (b)), the variable length code corresponding to the specific quantized value (FIG. (c)), and the correspondence table between the variable length code and the run and level (FIG. (D)) and a code string ((e)) in the bit stream corresponding to the specific quantized value.

FIG. 9 is a schematic diagram showing a structure of an encoded bit stream including a code including an identification bit of a final DCT coefficient in place of a code corresponding to a DCT coefficient and EOB data in the encoded bit stream of the embodiment. is there.

FIG. 10 is a diagram for explaining a variable length encoding process for generating an encoded bit stream including a code including an identification bit of the final DCT coefficient, and specifically illustrates a two-dimensional array of quantized values (FIG. a)), the scan order of the quantized values (see FIG.
(b)), a variable length code corresponding to the specific quantized value (FIG. (c)), a correspondence table between the variable length code, last, run, and level (FIG. (d)), and the specific quantum 5 shows a code string (FIG. 7E) in the bit stream corresponding to the coded value.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 digital image decoding device 100a variable length decoding unit 100b information source decoding unit 100b1 prediction value generation unit 102 shifter 103 code decoding unit 105 controller 106 switch 109 inverse quantizer 110 inverse DCT unit 111 adders 112, 115 1, second address generator 113 frame memory 114 motion vector scaling unit 200, 900 coded bit stream a, b, c, d DCT coefficient A, B, C, D quantized value Cs computer system F frequency space FD Floppy disk FDD Floppy disk drive S Scan order T, Ta Variable length coding table

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 9/793 H04N 9/79 L

Claims (10)

[Claims] 1. A digital image decoding method for decoding a compressed coded data including coded data obtained by coding a luminance signal and a color difference signal to reproduce an image signal for displaying an image. In a color display mode in which an image is displayed in color, both the encoded data of the luminance signal and the encoded data of the color difference signal are decoded. In a monochrome display mode in which an image is displayed in monochrome, the encoding of the luminance signal is performed. An image decoding method characterized in that only encoded data is decoded. 2. A digital image decoding method for decoding a compressed coded data including coded data obtained by coding a luminance signal and a chrominance signal to reproduce an image signal for displaying an image. In a color display mode in which an image is displayed in color, the decoding process includes a decoding process for decoding the coded compressed coded data, and a decoding process for decoding the decoded compressed coded data. In the monochrome display mode in which both the encoded signal data and the color difference signal data are decoded and the image is displayed in monochrome, during the decoding process, the encoded data of the color difference signal is detected and discarded, and the decoding is performed. An image decoding method, characterized in that only encoded data of a luminance signal is decoded by processing. 3. The image decoding method according to claim 2, wherein said coded compressed coded data includes a code corresponding to a plurality of transform coefficients obtained by frequency-converting said luminance signal, and said chrominance signal. And a code string corresponding to a plurality of conversion coefficients obtained by performing frequency conversion, and a bit string sequentially arranged with control data in correspondence with a unit processing area of a fixed size on the display screen. In the decoding process, the code corresponding to the final transform coefficient of the luminance signal corresponding to the unit processing area and the code corresponding to the final transform coefficient of the color difference signal are detected, and the code next to the code corresponding to the final transform coefficient of the luminance signal is detected. A feature is to discard all the conversion coefficient codes from the code corresponding to the first conversion coefficient of the arranged color difference signals to the code corresponding to the final conversion coefficient of the color difference signal. Picture decoding method according to. 4. The image decoding method according to claim 3, wherein the detection of the code corresponding to each of the final transform coefficients is performed by detecting a code immediately before the code corresponding to the final transform coefficient in the bit string. Is performed based on index data indicating that the code is a code corresponding to the final transform coefficient. 5. The image decoding method according to claim 3, wherein a code corresponding to each of the transform coefficients includes an identification bit indicating whether or not the transform coefficient is the final transform coefficient. An image decoding method, characterized in that: 6. A difference value between each signal and its predicted value is generated from a luminance signal and a color difference signal for each unit processing area on a display screen, and the difference value corresponding to each signal is obtained by frequency conversion. A digital image decoding method that performs a decoding process on compression-encoded data including a transform coefficient and a motion vector generated with the generation of a prediction value of the luminance signal to reproduce an image signal for performing image display. In a color display mode in which an image is displayed in color, a difference value restoration process for restoring a conversion coefficient corresponding to the luminance signal and the color difference signal into a luminance difference value and a color difference difference value, respectively, Get the predicted value of,
A luminance signal reproduction process for reproducing a luminance signal by adding the predicted value and the luminance difference value; a scaling process for converting a scale of a motion vector corresponding to the luminance signal to a value corresponding to the color difference signal;
And obtaining a predicted value of the color difference signal using the scaled motion vector, performing a color difference signal reproduction process of reproducing the color difference signal by adding the predicted value and the color difference signal, and displaying a monochrome image. In the display mode, instead of the respective processes in the color display mode, a difference value restoration process for restoring a transform coefficient corresponding to the luminance signal to a luminance difference value, and a prediction value of the luminance signal is obtained using the motion vector. And performing a reproduction process of reproducing a luminance signal by adding the prediction value and the luminance difference value. 7. A digital image decoding apparatus for decoding a compressed coded data including coded data obtained by coding a luminance signal and a chrominance signal to reproduce an image signal for displaying an image. A mode determining means for determining which of a color display mode in which images are displayed in color and a monochrome display mode in which images are displayed in monochrome is set; and receiving the output of the mode determining means, In the display mode, the encoded data of the luminance signal and the encoded data of the color difference signal are output. In the monochrome display mode, the encoded data of the luminance signal is output and the encoded data of the color difference signal is discarded. An image decoding apparatus, comprising: a selection unit; and a decoder that decodes encoded data output from the data selection unit. 8. The image decoding apparatus according to claim 7, wherein the compressed coded data includes a plurality of luminance conversion coefficients obtained by performing an encoding process including a frequency conversion on the luminance signal, and A coded bit sequence including a plurality of color difference conversion coefficients obtained by performing an encoding process including a frequency conversion on the signal, wherein the data selection unit has a data decoder for decoding the bit sequence, and performs color display. In the mode, the luminance conversion coefficient and the chrominance conversion coefficient obtained by decoding the bit string are output. In the monochrome display mode, the chrominance conversion coefficient among the conversion coefficients obtained by decoding the bit string is discarded, and only the luminance conversion coefficient is discarded. The decoder decodes the transform coefficient output from the data selection means by a decoding process including an inverse frequency conversion process. An image decoding apparatus characterized in that the image decoding apparatus is configured to perform decoding. 9. A difference value between each signal and its predicted value is generated from a luminance signal and a color difference signal for each unit processing area on a display screen, and the difference value corresponding to each signal is obtained by frequency conversion. A digital image for reproducing an image signal for performing image decoding by performing a decoding process on coded compressed encoded data including a transform coefficient and a motion vector generated along with generation of a predicted value of the luminance signal. A decoding device, comprising: a frame memory for storing reproduced luminance reproduction signals and color difference reproduction signals; a color display mode for displaying images in color; and a monochrome display mode for displaying images in monochrome. Mode determining means for determining whether or not the setting has been set; decoding the coded compressed coded data to obtain a conversion coefficient corresponding to the luminance signal and the chrominance signal; Receiving the output of the mode determining means, outputting the conversion coefficients of the luminance signal and the color difference signal in the color display mode, and discarding the conversion coefficient of the color difference signal in the monochrome display mode. A data selection unit that outputs only the conversion coefficient of the luminance signal, and performs a decoding process including an inverse frequency conversion process on the conversion coefficient output from the data selection unit to obtain a difference value of the luminance signal or the chrominance signal. Receiving the output of the mode discriminating means, in the color display mode, obtaining a predicted value of a luminance signal from the frame memory using the motion vector, and obtaining a motion vector corresponding to the luminance signal. Is converted to a scale corresponding to the color difference signal, and the scaled motion vector is A motion compensator that obtains a predicted value of a color difference signal from the frame memory and obtains a predicted value of a luminance signal from the frame memory using the motion vector in the monochrome display mode; A luminance reproduction signal or a chrominance reproduction signal is generated by adding the prediction value of the luminance signal or the difference value of the chrominance signal and the prediction value of the chrominance signal, and at the same time, the luminance reproduction signal and the chrominance reproduction signal are converted into the frame. An image decoding device, comprising: an adder for storing the image in a memory. 10. A data storage medium storing an image processing program, wherein the image processing program causes a computer to perform image processing by the image decoding method according to any one of claims 1 to 6. A data storage medium characterized in that the data storage medium is an image processing program.