JP2009124585A - Image coding apparatus and image coding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve coding efficiency by preventing the code amount of unnecessary color signals from being generated. <P>SOLUTION: A luminance signal and a color difference signal are divided into fixed blocks in such a way as to perform prediction coding and transformation coding to the blocks. A first threshold and a second threshold are then determined for the luminance signal. If all levels of the luminance signals within the block are lower than the first threshold or higher than the second threshold; and the block performs intra-prediction, the color difference signal is permuted with a DC prediction signal. Furthermore, if the block performs inter-prediction, the color difference signal is substituted with a prediction signal or a flag indicating absence of a differential signal is raised, thereby reducing the code amount of the color difference signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image encoding device and an image encoding method, and more particularly to a technique suitable for use in performing encoding processing by converting image data into a luminance signal and a color difference signal.

  Conventionally, when compressing and encoding image data, as shown in FIG. 9, after the image data is converted into a luminance signal and a color difference signal by the color conversion unit, the block division unit further converts a certain pixel unit. The data is divided into blocks, and encoding processing such as prediction and conversion processing is performed in units of the blocks. Hereinafter, a representative color conversion method and encoding processing method will be briefly described.

  When the image data is expressed in the three primary colors RGB, it is converted into a luminance signal Y and two color difference signals Cb and Cr prior to normal compression processing. In the well-known BT601 system, conversion is performed according to the following equation.

  The luminance signal and color difference signal thus converted are usually expressed with an accuracy of 8 bits respectively. When the original RGB value is from 0 to 1, the range of the luminance signal and the color difference signal that are valid according to each standard is 16 <Y <235, 16 <Cb, Cr <240. Furthermore, the range that the color difference signals Cb and Cr can take is limited by the value of the luminance signal Y.

  This is shown in FIG. In FIG. 10, the vertical axis represents the luminance signal Y, and the horizontal axis represents the possible range of the color difference signals Cb and Cr. Here, since the resolution required for the color difference signal is lower than that of the luminance signal Y, the color difference signal is often further subjected to sub-sampling processing so that the number of data is smaller than that of the luminance signal. The methods of “4: 2: 2, 4: 2: 0” and “4: 1: 1” are often used.

JP-A-5-153407 JP 2004235811 A

  By the way, as human visual characteristics, it is known that the color recognizable range varies depending on the magnitude of the luminance signal. That is, as shown in FIG. 10, in the combination represented by the 8-bit luminance signal and the color difference signal, the range where the color can be visually perceived is limited to the rhombus (thick line portion) in FIG. . For example, when the luminance signal is small (when dark), the color is hardly felt.

  Further, even when the luminance signal is large (when bright), the color is hardly felt. In particular, when the luminance signal exceeds a predetermined maximum value of 235, it is perceived as almost white (not visually recognized). Conventionally, even a color difference signal exceeding human visual characteristics is compressed by a normal encoding process and added to the compressed data.

For this reason, since encoding processing is also performed for color signals that cannot be visually recognized in the past, an unnecessary code amount of color signals is generated, which hinders improvement in encoding efficiency.
An object of the present invention is to prevent the generation of an unnecessary code amount of a color signal and to improve the encoding efficiency in view of the above-described problems.

An image encoding apparatus according to the present invention is an image encoding apparatus that decomposes image data including a luminance component and a color difference component into blocks each including a plurality of pixels, and performs an encoding process in units of the blocks. Range detection means for detecting whether the value of the luminance component in the unit is outside the predetermined range, and the value of the luminance component in the block unit is outside the predetermined range as a result of detection by the range detection means In this case, the image processing apparatus includes code assigning means for assigning a code having the smallest code amount to the color difference component in the block unit regardless of the component.
Another feature of the image coding apparatus according to the present invention is that the image data composed of the luminance component and the chrominance component is decomposed into blocks each composed of a plurality of pixels, and the image is subjected to coding processing in units of the blocks. An encoding device, wherein the luminance component value in the block unit is encoded by performing quantization processing, and the luminance component value in the block unit encoded by the encoding unit is decoded. Whether the luminance component value filtered by the filtering means, the filtering processing means for filtering the luminance component value decoded by the decoding means, is out of a predetermined range A range detecting unit for detecting whether or not the luminance component value within the block unit is outside a predetermined range as a result of detection by the range detecting unit; The color difference component in a unit, and having a code assigning means for assigning a small code most code amount regardless of its components.
Another feature of the image coding apparatus according to the present invention is that the image data composed of the luminance component and the chrominance component is decomposed into blocks each composed of a plurality of pixels, and the image is subjected to coding processing in units of the blocks. An encoding device, wherein the luminance component value in the block unit is detected as a result of detection by the range detection unit for detecting whether the value of the luminance component in the block unit is outside a predetermined range. If the value of the block is outside the predetermined range, if the block outside the predetermined range is subjected to intra processing, the block is predicted in a specific prediction mode, and all the values of the color difference components in the block are predicted. A color difference component replacement unit that replaces the color difference component in the block with the color difference component of the inter prediction destination when the block is inter-processed and replaced with the predicted value of the mode. And butterflies.

An image encoding method according to the present invention is an image encoding method in which image data composed of a luminance component and a color difference component is decomposed into blocks each composed of a plurality of pixels, and an encoding process is performed for each block. A range detecting step for detecting whether or not the value of the luminance component in the unit is outside the predetermined range, and the result of detection in the range detecting step is that the value of the luminance component in the block unit is outside the predetermined range In this case, the method includes a code assigning step for assigning a code having the smallest code amount to the color difference component in the block unit regardless of the component.
Another feature of the image coding method according to the present invention is that an image is divided into block units each composed of a plurality of pixels, and the image is subjected to coding processing in units of blocks. An encoding method comprising: encoding a luminance component value in the block unit by performing quantization processing and encoding; and decoding the luminance component value in the block unit encoded in the encoding step Whether the luminance component value filtered in the decoding step, the filtering processing step for filtering the luminance component value decoded in the decoding step, and the luminance component value filtered in the filtering step are out of a predetermined range A range detection step for detecting whether or not the luminance component value in the block unit is outside a predetermined range as a result of detection in the range detection step; The color difference components in the block units, and having a code assignment step for assigning a small code most code amount regardless of its components.
Another feature of the image coding method according to the present invention is that an image in which image data composed of a luminance component and a color difference component is decomposed into blocks each composed of a plurality of pixels, and coding processing is performed in blocks. A range detection step for detecting whether or not a value of a luminance component in the block unit is outside a predetermined range, and a luminance component in the block unit as a result of detection in the range detection step. If the value of the block is outside the predetermined range, if the block outside the predetermined range is subjected to intra processing, the block is predicted in a specific prediction mode, and all the values of the color difference components in the block are predicted. A color difference component replacement step of replacing the color difference component in the block with the color difference component of the inter prediction destination when the block is inter-processed and replaced with the predicted value of the mode And wherein the door.

The program according to the present invention is a program for causing a computer to execute a process of decomposing image data including a luminance component and a color difference component into blocks each including a plurality of pixels and performing an encoding process on each block. A range detecting step for detecting whether or not the value of the luminance component in the unit is outside the predetermined range, and the result of detection in the range detecting step is that the value of the luminance component in the block unit is outside the predetermined range In this case, the computer is caused to execute a code assigning step for assigning a code having the smallest code amount regardless of the component to the color difference component in the block unit.
Another feature of the program of the present invention is that the process of decomposing the image data composed of the luminance component and the color difference component into a block unit composed of a plurality of pixels and performing the encoding process in the block unit is performed on the computer. A program to be executed, wherein the luminance component value in the block unit is encoded by performing a quantization process, and the luminance component value in the block unit encoded in the encoding step is decoded. Whether the luminance component value filtered in the decoding step, the filtering processing step for filtering the luminance component value decoded in the decoding step, and the luminance component value filtered in the filtering step are out of a predetermined range As a result of the detection in the range detection step and the range detection step, the value of the luminance component in the block unit is a predetermined range. If it is outside, the color difference component of said block unit, characterized in that to execute a code assignment step for assigning the most code amount less code regardless of its components in a computer.
Another feature of the program of the present invention is that the image data composed of the luminance component and the chrominance component is decomposed into a block unit composed of a plurality of pixels, and the process of performing the encoding process in the block unit is performed on the computer. A range detection step for detecting whether the value of the luminance component in the block unit is outside a predetermined range, and a luminance component in the block unit as a result of detection in the range detection step If the value of the block is outside the predetermined range, if the block outside the predetermined range is subjected to intra processing, the block is predicted in a specific prediction mode, and all the values of the color difference components in the block are predicted. When the block is inter-processed with the mode prediction value, the color difference in the block is replaced with the inter-prediction destination color difference component. Characterized in that to execute the divided substitution process on the computer.

  According to the present invention, the code amount for the color signal in the block, which is a luminance signal whose color is difficult to recognize due to human visual characteristics, is reduced by a method suitable for the prediction method. The generation of the code amount can be prevented, and the encoding efficiency can be improved.

(First embodiment)
First, the background art of the image coding apparatus according to the present embodiment will be described.
A typical encoding processing method for performing compression processing on a luminance signal (luminance component) and a color difference signal (color difference component) will be described.
FIG. 11 is a block diagram showing a configuration example of an image encoding apparatus in the MPEG2 system. In FIG. 11, 1100 is a control unit comprising a CPU, a ROM, and a RAM, and controls the entire image encoding apparatus and color signal processing of this embodiment. Reference numeral 1101 denotes an input image signal. The input image signal 1101 is temporarily stored in an input buffer (not shown) and then subjected to necessary rearrangement and block division.

  Reference numeral 1102 denotes a differentiator that outputs a difference signal between the input image signal and the prediction signal. 1103 is a prediction mode switch, and switches a prediction destination to an intra prediction destination or an inter prediction destination. Specifically, switching between intra prediction (switch is on the b side) or inter prediction (switch is on the a side) is performed. Reference numeral 1104 denotes a DCT converter, and 1105 denotes a quantizer. Reference numeral 1106 denotes a variable length encoder, and 1107 denotes a DC prediction value in intra prediction.

  Reference numeral 1108 denotes an output signal, which is a signal that has been compression-encoded in the image encoding apparatus. Reference numeral 1109 denotes an inverse quantizer, and 1110 denotes an inverse DCT converter. Reference numeral 1111 denotes an adder that creates a reference image from the inversely converted difference signal. Reference numeral 1112 denotes a frame memory, 1113 denotes a motion compensation unit (MC unit), and 1114 denotes a motion detection unit (ME unit).

  In the image coding apparatus configured as described above, the input image signal 1101 is divided into macro blocks. When performing intra coding without performing inter-frame prediction, DCT conversion (Discrete Cosine Transform) is performed in the DCT converter 1104 on the image data as it is.

  Further, in inter coding for performing inter-frame prediction, a difference signal 1102 is obtained using image data of a block predicted from a different frame as a prediction signal, and discrete cosine transform is performed on the difference signal 1102. After the discrete cosine transform, the quantizer 1105 performs quantization processing with the set quantization value (Q value), and then the variable length encoder 1106 performs variable length encoding, and adds necessary header information and the like. Thus, an output signal 1108 is generated.

  On the other hand, among the quantized data, image data to be used as a reference image for inter prediction is internally inversely quantized by an inverse quantizer 1109 and then inversely DCT transformed by an inverse DCT transformer 1110. Then, after performing inverse DCT transform, the signal is input to the adder 1111 and added to the prediction signal, accumulated in the frame memory 1112, and used as a reference image in inter prediction.

  In FIG. 11, a motion detection unit 1114 detects a motion between frames, encodes a motion vector as header information, and a motion compensation unit 1113 performs motion compensation that creates a prediction signal from a reference image.

  Here, FIG. 12 shows typical blocks of luminance and chrominance mainly used in the MPEG2 system (described in the 4: 2: 0 system). In the MPEG2 system, the luminance signal is divided into 16 × 16 pixel units, and the corresponding two color difference signals are divided into 8 × 8 pixel units, which are collectively handled as one macro block.

  For the intra-coded macro block, after DCT conversion, as shown in FIG. 13, DC prediction using the DC value of the adjacent block as a predicted value is performed, and the prediction error is encoded.

  On the other hand, when inter prediction is performed as shown in FIG. 14, the correlation with the reference image is examined in units of macroblocks, and the block having the highest correlation is used as a prediction signal, and the difference signal is encoded. Note that the luminance signal and the color difference signal of the same macroblock are encoded using the same motion vector.

  In the case of inter prediction, the presence / absence of a DCT coefficient performed in units of 8 × 8 is described as a coded block pattern (CBP). CBP is represented by 6 bits in the 4: 2: 0 system, and each bit corresponds to a block of 8 × 8 units as shown in FIG. When the CBP bit is 1, it indicates that there is a DCT coefficient of the corresponding block and this is encoded. For example, if a block filled with diagonal lines in FIG. 15 has a DCT coefficient and other blocks do not have a DCT coefficient, CBP represents “100110 (binary number)”.

  Furthermore, as a new encoding method, an encoding method called MPEG4 Part-10 AVC or H.264 (hereinafter referred to as H.264) has appeared. FIG. 16 shows an H.264 encoding method.

  In FIG. 16, reference numeral 1600 denotes a control unit composed of a CPU, a ROM, and a RAM, which controls the entire image encoding apparatus of this embodiment and performs color signal processing. Reference numeral 1601 denotes an input image signal. The input image signal 1601 is temporarily stored in an input buffer (not shown) (not shown), and then necessary rearrangement and block division are performed. Reference numeral 1602 denotes a differentiator that outputs a difference signal between the input image signal and the prediction signal. Reference numeral 1603 denotes a prediction mode switch, which switches between intra prediction (switch is on the b side) or inter prediction (switch is on the a side). Reference numeral 1604 denotes an integer converter.

  Reference numeral 1605 denotes an entropy encoder that performs variable length coding (CAVLC) or arithmetic coding (CABAC). Reference numeral 1606 denotes an output signal, which is a signal that has been compression-encoded by the image encoding apparatus in FIG. Reference numeral 1607 denotes an inverse integer converter. Reference numeral 1608 denotes an adder that creates an intra prediction reference image from the inversely converted difference signal. Reference numeral 1609 denotes an intra prediction frame memory, and 1610 denotes an intra prediction unit. Reference numeral 1611 denotes an in-loop filter. Reference numeral 1612 denotes an inter prediction frame memory, and 1613 denotes an inter prediction unit. Reference numeral 1614 denotes a motion detection unit (ME unit).

  The input image signal 1601 is divided into macro blocks. In the case of intra coding that performs intra-frame prediction, neighboring pixels in the frame are used as a prediction signal. In the inter coding, the difference signal is obtained by using the image data of the block predicted from different frames as the prediction signal. The difference signal is subjected to integer conversion including quantization in the integer converter 1604 and entropy encoding (CAVLC or CABAC) is performed in the entropy encoder 1605. Thereafter, necessary header information and the like are added to generate an output signal 1606.

  On the other hand, the integer-converted data is subjected to inverse integer conversion by the inverse integer converter 1607 and added by the adder 1608, and is stored in the intra prediction frame memory 1609 as image data for intra prediction. From this data, the intra prediction unit 1610 determines an intra prediction mode and creates a prediction signal.

  Further, in the case of image data to be used as a reference image for inter prediction, intra-loop filter processing is performed by the in-loop filter 1611, accumulated in the inter prediction frame memory 1612, and used as a reference image for intra prediction. In FIG. 16, the motion detection unit 1614 detects the motion between frames, encodes the motion vector as header information, and the inter prediction unit (1613) creates a prediction signal from the reference image.

  Macroblocks used in the H.264 system are the same as the MPEG2 system in FIG. 12 in the 4: 2: 0 system. That is, the luminance signal is divided into 16 × 16 pixel units, and the corresponding two color difference signals are divided into 8 × 8 pixel units, which are collectively handled as one macro block.

Here, the H.264 intra prediction will be described with reference to FIG.
FIG. 17 shows an intra prediction method for color difference signals. For the color difference signal, four prediction directions are prepared with the surrounding pixels of the 8 × 8 pixel block as the prediction signal. Usually, a prediction direction with the smallest code amount is determined by comparing the prediction directions and used for intra prediction. As for the luminance signal, prediction in units of 4 × 4 pixels and prediction in units of 16 × 16 pixels are prepared, but the details are omitted.

  In H.264 inter prediction, functions such as a block (macroblock partition) having a smaller macroblock, which can select a plurality of reference pictures, are added. It is the same that the same vector is used for the luminance signal and the color difference signal of the same block, and the presence / absence of the coefficient after integer conversion is described as a coded block pattern. However, when the luminance signal performs intra 16 × 16 prediction, there are differences in description such as including a coded block pattern in the macro block type.

  Incidentally, Patent Document 1 is known as a problem when encoding a luminance signal and a color difference signal. This solves the problem when a color image and a black and white image are mixed. After the color conversion unit decomposes the luminance signal and the color difference signal, if the color difference signal is smaller than a preset value, only the luminance signal is displayed. Encoding is performed.

  Further, in Patent Document 2, when the result of conversion into a luminance signal and a color difference signal is a combination that cannot be generated, the luminance signal and the color difference signal are converted again, and the luminance signal and the color difference signal within a predetermined range are converted. As a result, the amount of code is reduced.

Next, a first embodiment of the present invention will be described with reference to FIG.
In FIG. 1, reference numeral 100 denotes a control unit composed of a CPU, a ROM, and a RAM, which controls the entire image encoding apparatus of this embodiment and performs color signal processing. Reference numeral 101 denotes an input image signal. The input image signal 101 is temporarily stored in an input buffer (not shown), and then necessary rearrangement and block division are performed. A difference unit 102 outputs a difference signal between the input image signal and the prediction signal. 103 is a prediction mode switch, and switches intra prediction or inter prediction.

  Reference numeral 104 denotes a DCT converter, and reference numeral 105 denotes a quantizer. Reference numeral 106 denotes a variable length encoder, and reference numeral 107 denotes a DC prediction value in intra prediction. Reference numeral 108 denotes an output signal, which indicates a compression-coded signal. Reference numeral 109 denotes an inverse quantizer, and 110 denotes an inverse DCT converter. Reference numeral 111 denotes an adder that creates a reference image from the inversely converted difference signal. Reference numeral 112 denotes a frame memory, 113 denotes a motion compensation unit (MC unit), and 114 denotes a motion detection unit (ME unit).

  Reference numeral 115 denotes a luminance signal detection unit that checks the level of the luminance signal in the macroblock. In a normal case, the operation performed by the motion detector 114 from the subtractor 102 is equivalent to the conventional MPEG2 encoding. However, for luminance signals, the inverse quantization performed by the inverse quantizer 109, the inverse DCT performed by the inverse DCT converter 110, and the addition processing performed by the adder 111 are images that are not used as reference images for inter prediction. Even if it is the data of, it processes.

  In the present embodiment, when the reference image is created by adding the prediction signal in the adder 111, the luminance signal detection unit 115 determines whether or not the level of the luminance signal in the macroblock unit is within a predetermined detection range. Investigate. In the present embodiment, the luminance signal detection unit 115 functions as a range detection unit, and specifies a predetermined range with a threshold 1 (first threshold) and a threshold 2 (second threshold) for the luminance level. deep. For example, 16 is given for the threshold value 1 and 235 is given for the threshold value 2.

  The luminance signal detection unit 115 compares the threshold value with the luminance signal level. If the luminance signal level is all lower than the threshold value 1 or higher than the threshold value 2, the luminance signal is out of the predetermined range. Are sent to the variable length encoder 106.

  In the variable-length encoder 106, when the luminance signal is out of the range, a code that hardly generates a code (unsigned) with respect to the color difference signal block of the macroblock regardless of the value of the difference signal. Process. In this embodiment, the variable-length encoder 106 functions as a color difference component replacement unit that replaces data with the least number of codes.

This will be described with reference to the flowchart of FIG. The following operations are executed under the control of the control unit 100 including a CPU, a ROM, and a RAM.
First, in step S201, variable-length coding is performed by the variable-length encoder 106, and data after macroblock conversion and quantization is acquired. Thereafter, in step S202, it is determined whether the encoding target is a color difference signal block.

  If the result of this determination is that the block is not a color difference signal block, that is, if it is a luminance signal block, the process proceeds to step S203 to perform normal encoding processing. If the result of determination in step S202 is a color difference signal block, the process proceeds to step S204 to determine the result of examining the luminance level performed by the luminance signal detection unit 115.

  If the result of determination in step S204 is that the luminance signal is within the range, processing proceeds to step S203, and normal encoding processing is performed. On the other hand, if the result of determination in step S204 is that the luminance signal is out of range, the process proceeds to processing for assigning a specific code regardless of the data value of the acquired color difference signal block. That is, first, in step S205, it is determined whether the prediction of the block is inter prediction. If the result of this determination is not inter prediction, that is, if intra processing has been performed, processing proceeds to step S206 and intra processing is performed. If the result of determination in step S205 is inter prediction, the process proceeds to step S207 to perform inter processing.

  In the intra processing performed in step S206, the color difference signal data is encoded assuming that the DC component is equal to the DC predicted value 107 and the AC component is all 0 regardless of the data acquired in step S201. I do. That is, for the DC component, since it is the difference value of the DC prediction that is encoded, 0 is encoded as this difference value. Since the AC component thereafter is 0, no code is generated, and EOB (End of Block) is immediately encoded, and the encoding process of the block is completed.

  In the case of the inter processing in step S207, the data of the color difference signal component is encoded on the assumption that all the components are 0 regardless of the data acquired in step S201. That is, no direct code is generated for the color signal component data, and only the bit string corresponding to the CBP color difference block is changed. That is, the bit sequence (the lower two digits in binary display) corresponding to the CBP color difference block is set to 0, and the coding process of the block is terminated assuming that there is no color difference signal component data.

  Through the above processing, the macro block whose luminance signal is out of the predetermined range is encoded with the luminance signal as usual, and the color signal is encoded so that the code hardly occurs.

  When the macroblock encoded in this way is decoded, the luminance component is decoded as usual. As for the color difference component, when intra processing is performed, all the color difference signals of the macroblock are signals having a value equal to the DC prediction value, and when inter processing is performed, they are equal to the color difference signal that is the reference destination of inter prediction. It becomes a signal of value.

  That is, the color difference component may be decoded as a value that is significantly different from the color difference signal before encoding. However, the luminance signal value at this time is in a range where it is difficult to recognize colors as human visual characteristics. That is, the luminance signal is lower than the threshold 1 set at the time of encoding or higher than the threshold 2. Therefore, even if the decoded color difference signal is significantly different from the color difference signal before encoding, almost no coding deterioration is felt.

  As described above, according to the present embodiment, the code of the color difference signal is hardly generated for the macroblock whose luminance signal level is in a range where the color cannot be recognized. As a result of performing such an encoding process, it is possible to reduce the amount of codes of the entire image data and to improve the encoding efficiency.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.
FIG. 3 shows a second embodiment according to the present invention. In the second embodiment, the level of the luminance signal is checked for the input image data, and if this level is outside the predetermined range, the value of the color difference signal is replaced using the prediction signal.

  In FIG. 3, a control unit 300 includes a CPU, a ROM, and a RAM, and controls the entire image encoding apparatus and color signal processing according to the present embodiment. An input image signal 301 is temporarily stored in an input buffer (not shown) and then subjected to necessary rearrangement and block division. Reference numeral 302 denotes a differentiator that outputs a difference signal between the input image signal 301 and the prediction signal. A prediction mode switching unit 303 switches between intra prediction and inter prediction. Reference numeral 304 denotes a DCT converter, and 305 denotes a quantizer.

  Reference numeral 306 denotes a variable length encoder, and reference numeral 307 denotes a DC prediction value in intra prediction. Reference numeral 308 denotes an output signal, which indicates a compression-coded signal. Reference numeral 309 denotes an inverse quantizer, and 310 denotes an inverse DCT converter. Reference numeral 311 denotes an adder that creates a reference image from the inversely converted difference signal. Reference numeral 312 denotes a frame memory, 313 denotes a motion compensation unit (MC unit), and 314 denotes a motion detection unit (ME unit).

  Reference numeral 315 denotes a luminance signal detection unit for checking the level of the luminance signal in the macroblock. A color difference signal replacement unit 316 replaces the value of the color difference signal with a predicted value in accordance with the detection result of the luminance signal detection unit 315.

In a normal case, each unit from the subtractor 302 to the motion detection unit 314 performs an operation equivalent to the conventional MPEG2 encoding.
In this embodiment, the luminance signal detection unit 315 checks whether or not the level of the luminance signal in units of macroblocks is within a predetermined range for the input image data. Then, as in the first embodiment described above, a predetermined range is specified with threshold values 1 and 2 for the luminance level. For example, 16 is given for the threshold value 1 and 235 is given for the threshold value 2.

  The luminance signal detection unit 315 compares the threshold value with the luminance signal level. If the luminance signal level is all lower than the threshold value 1 or higher than the threshold value 2, the luminance signal is outside the predetermined range. The detection result is sent to the color difference signal replacement unit 316.

  When the luminance signal is out of range, the color difference signal replacement unit 316 replaces the value of the difference signal with the value of the prediction signal for the block of the color difference signal of the macroblock. This will be described with reference to the flowchart of FIG. The following operations are executed under the control of the control unit 300 including a CPU, a ROM, and a RAM.

  First, in step S401, variable length coding is performed by the variable length encoder 306, and macroblock data of input image data is acquired. Thereafter, the process proceeds to step S402, where it is determined whether the encoding target is a color difference signal block. If the result of this determination is that the block is not a color difference signal block, that is, if it is a luminance signal block, no processing is performed and the processing proceeds to the next processing (the processing of the flowchart of FIG. 4 ends).

  On the other hand, if it is determined in step S402 that the color difference signal block is to be encoded, the process proceeds to step S403 to determine the result of examining the luminance level performed by the luminance signal detection unit. If the result of this determination is that the luminance signal is within the range, no process is performed and the process proceeds to the next process (the process of the flowchart of FIG. 4 is terminated). If the result of determination in step S403 is that the luminance signal is out of range, the value of the color difference signal is replaced with the value of the prediction signal for that color difference signal block regardless of the data value of the acquired color difference signal block. Transition to processing.

  That is, first, in step S404, it is determined whether the prediction of the block is inter prediction. If the result of this determination is that it is not inter prediction, that is, if intra processing has been performed, processing proceeds to step S405, where intra DC replacement is performed. If the result of determination in step S404 is inter prediction, the process proceeds to step S406 to perform inter prediction replacement.

  In the intra DC replacement in step S405, all the data of the color difference signal is replaced with the DC predicted value 307 regardless of the data acquired in step S401. In the case of inter prediction replacement in step S406, the color difference signal component data is replaced with the prediction signal sent from the motion compensation unit 313 regardless of the data acquired in step S401.

  When the color difference signal is replaced by the color difference signal replacement unit 316, the code for the color difference signal is hardly generated. That is, when the intra DC replacement is performed in step S405, all the color difference signal data of the macro block becomes equal to the DC prediction value 307 in the intra prediction. Therefore, after the DCT conversion by the DCT converter 304, only the DC component remains in the color difference signal data, and the AC component is all zero.

  Next, this DC component is quantized by the quantizer 305, but when quantized with the same value as the Q value of the adjacent block, the value after quantization is also equal to the DC predicted value. For this reason, as a result of performing DC prediction by variable length coding by the variable length encoder 306, the prediction error becomes zero. In other words, the color difference signal data to be encoded is all 0, and almost no code is generated.

  When the quantization in the quantizer 305 is quantized with a value different from the Q value of the adjacent block, a value different from the DC prediction value is output. Even in this case, as a result of performing DC prediction by variable length coding by the variable length encoder 306, the prediction error that occurs is only a small value. Therefore, the color difference signal data to be encoded is a slight DC prediction error and an AC coefficient that is 0, and almost no code is generated.

  On the other hand, when the inter prediction replacement is performed in step S406, the color difference signal data of the macroblock is equal to the color difference signal data predicted by the motion compensation unit 313. In other words, the residuals of the color difference signals output from the subtractor 302 are all zero. Accordingly, even after DCT conversion by the DCT converter 304 and quantization by the quantizer 305, all the color difference signal data remains 0. For this reason, in the variable length coding by the variable length coder 306, all data is 0. Therefore, the encoding process is performed assuming that the bit corresponding to the color difference block of CBP is set to 0 (the lower two digits in binary display) and there is no color difference signal component data. For this reason, a code corresponding to the color difference signal is not generated.

  In this embodiment, the level of the luminance signal is checked for the input image data, and if this level is outside the predetermined range, the value of the color difference signal is replaced using the prediction signal. As a result, the macro block whose luminance signal is out of the predetermined range is encoded as usual for the luminance signal, and is encoded so that the code is hardly generated for the color signal.

  On the other hand, unlike the case of the first embodiment, in this embodiment, processing is performed on input image data. For this reason, when the Q value for the macroblock changes, the decoded luminance value may be out of the predetermined range due to the influence of the quantization error, or the code for the color difference data may be slightly more than in the first embodiment. Occur.

  However, in the present embodiment, the detection of the luminance signal and the replacement process of the color difference signal are performed as a process before the main part of the encoding process (from the differencer 302 to the motion detection unit 314). The function of this embodiment can be added without changing the operation of the unit. That is, the present embodiment can be realized as preprocessing even when an existing image encoding apparatus in which the main part of the encoding process is configured by hardware or the like is used.

  In FIG. 3, the intra DC prediction value is input to the color difference signal replacement unit 316 from an existing image encoding device. However, it is possible to provide means for detecting and storing the DC value of the color difference signal of the adjacent macroblock in the color difference signal replacement unit 316 instead of the intra DC predicted value. That is, a DC value (equal to the average value) is obtained for the color difference signals of adjacent blocks, stored, and used as a DC predicted value for the intra DC replacement performed in step S405. In this case, the prediction residual generated by the variable length coding by the variable length coder 306 may increase somewhat, but the image coding apparatus of this embodiment is completely independent of the existing image coding apparatus. Can be realized.

  In the present embodiment, the luminance signal is also described as being out of the predetermined range after decoding due to the influence of the quantization error. However, since the influence is generally limited to the level of quantization error, it remains the luminance signal level that makes it difficult to recognize the color signal. Therefore, even if the decoded color difference signal is significantly different from the color difference signal before encoding, almost no coding deterioration is felt.

  As described above, in the present embodiment, the luminance signal detection and the color difference signal processing are performed as preprocessing for encoding. As a result, the image coding apparatus according to the present embodiment can be realized with almost no change to the existing image coding apparatus. That is, almost no sign of the color difference signal is generated for a macroblock whose luminance signal level is in a range where the color cannot be recognized. As a result of performing such an encoding process, it is possible to reduce the amount of codes of the entire image data and to improve the encoding efficiency.

(Third embodiment)
FIG. 5 shows a third embodiment according to the present invention. The third embodiment is a case where a configuration equivalent to that of the first embodiment is applied to the H.264 encoding method. In FIG. 5, a control unit 500 includes a CPU, a ROM, and a RAM, and controls the entire image encoding apparatus and color signal processing according to the present embodiment. Reference numeral 501 denotes an input image signal which is temporarily stored in an input buffer (not shown) and then subjected to necessary rearrangement and block division. Reference numeral 502 denotes a differentiator that outputs a difference signal between the input image signal and the prediction signal.

  A prediction mode switch 503 switches between intra prediction (switch is on the b side) or inter prediction (switch is on the a side). Reference numeral 504 denotes an integer converter. Reference numeral 505 denotes an entropy encoder that performs variable length coding (CAVLC) or arithmetic coding (CABAC). Reference numeral 506 denotes an output signal indicating a compression-coded signal. Reference numeral 507 denotes an inverse integer converter. An adder 508 creates an intra prediction reference image from the inversely converted difference signal. Reference numeral 509 denotes an intra prediction frame memory, and 510 denotes an intra prediction unit. Reference numeral 511 denotes an in-loop filter. 512 is an inter prediction frame memory, and 513 is an inter prediction unit. Reference numeral 514 denotes a motion detection unit (ME unit).

Reference numeral 515 denotes a luminance signal detection unit that checks the level of the luminance signal in the macroblock.
In a normal case, the motion detector 514 from the subtractor 502 performs an operation equivalent to the conventional H.264 encoding. However, with respect to the luminance signal, the inverse integer conversion process of the inverse integer converter 507, the addition process of the adder 508, and the in-loop filter process of the in-loop filter 511 are image data that is not used as a reference image for inter prediction. Also do the processing.

  In the image coding apparatus of the present embodiment, when the adder 508 adds the prediction signal and the in-loop filter 511 finishes the in-loop filter processing, the luminance signal detection unit 515 determines the level of the luminance signal in units of macroblocks. Check whether it is within the predetermined range.

  Here, as in the first embodiment, a predetermined range is designated with the threshold 1 and the threshold 2 for the luminance level. For example, 16 is given for the threshold value 1 and 235 is given for the threshold value 2. The luminance signal detection unit 515 compares the threshold value with the luminance signal level. If the luminance signal level is all lower than the threshold value 1 or higher than the threshold value 2, the luminance signal is out of the predetermined range. To the entropy encoder 505.

  In the entropy encoder 505, when the luminance signal is out of range, an encoding process is performed on the color difference signal block of the macroblock so that almost no code is generated regardless of the value of the difference signal. Can do.

This will be described with reference to the flowchart of FIG.
In step S601, macro block data is acquired. Thereafter, in step S602, it is determined whether or not the color difference signal block. If it is determined in step S602 that the block is not a color difference block, the process proceeds to step S603 to perform normal encoding processing. If the result of determination in step S602 is a color difference block, the process proceeds to step S604.

  The determination of the luminance level in step S604 and the determination of whether or not to perform inter prediction in step S605 are performed in the same manner as in the first embodiment. As a result of the determination in step S605, if the prediction of the block is not inter prediction, that is, if intra processing has been performed, the process proceeds to step S606 to perform intra processing. If the result of determination in step S605 is inter prediction, the process proceeds to step S607 to perform inter processing.

  In the intra processing performed in step S606, the color difference signal data is encoded on the assumption that the prediction residual is zero in a specific intra prediction mode regardless of the data acquired in step S601 and the intra prediction mode. Do. For example, a specific intra prediction mode is set to DC prediction. The predicted value is a value obtained from adjacent pixels, and the predicted residual with this is assumed to be zero.

  Therefore, there is no encoding target for the color difference signal data of this macro block, and this is described in the coded block pattern. That is, it describes that the coded block pattern is included in the macro block type when the prediction of the luminance signal is intra 16 × 16 prediction. Otherwise, it is described that there is no color difference residual data in the part corresponding to the color difference signal of the independent coded block pattern.

  In the case of the inter processing in step S607, the color difference signal component data is encoded assuming that all the components are 0 regardless of the data acquired in step S601. That is, it describes that there is no color difference residual data in the portion corresponding to the color difference signal of the coded block pattern.

  As described above, according to the present invention, in a macroblock whose luminance signal is out of the predetermined range, the luminance signal is encoded in the conventional manner, and the code is hardly generated for the color signal. Is encoded. As a result, the code amount of the entire image data can be reduced, and the encoding efficiency is improved.

(Fourth embodiment)
Next, a fourth embodiment of the image encoding device of the present invention will be described with reference to FIG.
The image coding apparatus according to the fourth embodiment is a case where a configuration equivalent to that of the second embodiment is applied to the H.264 coding method. In FIG. 7, reference numeral 700 denotes a control unit including a CPU, a ROM, and a RAM, which controls the entire image encoding apparatus of this embodiment and performs color signal processing.

  Reference numeral 701 denotes an input image signal which is temporarily stored in an input buffer (not shown) and then subjected to necessary rearrangement and block division. Reference numeral 702 denotes a differentiator that outputs a difference signal between the input image signal and the prediction signal. A prediction mode switching unit 703 performs switching between intra prediction (switch is on the b side) or inter prediction (switch is on the a side). Reference numeral 704 denotes an integer converter. Reference numeral 705 denotes an entropy encoder, which performs variable length coding (CAVLC) or arithmetic coding (CABAC). Reference numeral 706 denotes an output signal indicating a compression-coded signal.

  Reference numeral 707 denotes an inverse integer converter. Reference numeral 708 denotes an adder that creates an intra prediction reference image from the inversely converted difference signal. Reference numeral 709 denotes an intra prediction frame memory, and reference numeral 710 denotes an intra prediction unit. Reference numeral 711 denotes an in-loop filter. Reference numeral 712 denotes an inter prediction frame memory, and reference numeral 713 denotes an inter prediction unit. Reference numeral 714 denotes a motion detection unit (ME unit).

  Reference numeral 715 denotes a luminance signal detection unit that checks the level of the luminance signal in the macroblock. Reference numeral 716 denotes a color difference signal replacement unit that replaces the value of the color difference signal with a predicted value in accordance with the detection result of 715. In a normal case, the motion detector 714 from the differentiator 702 performs an operation equivalent to the conventional H.264 encoding.

  In the image coding apparatus according to the present embodiment, as in the second embodiment, whether or not the level of the luminance signal in units of macroblocks is within a predetermined range by the luminance signal detection unit 715 for input image data. Check out. As in the first embodiment, a predetermined range is specified with threshold values 1 and 2 for the luminance level. For example, 16 is given for the threshold value 1 and 235 is given for the threshold value 2. The luminance signal detection unit 715 compares the threshold value with the luminance signal level. If the luminance signal level is all lower than the threshold value 1 or higher than the threshold value 2, the luminance signal is out of the predetermined range. Is sent to the color difference signal replacement unit 716.

  When the luminance signal is out of range, the color difference signal replacement unit 716 replaces the value of the difference signal with the value of the prediction signal for the color difference signal block of the macroblock. This will be described with reference to the flowchart of FIG.

  The acquisition of macroblock data in step S801, the determination of whether or not the color difference signal block is in step S802, the determination of the luminance level in step S803 and the determination of inter prediction in step S804 are performed in the same manner as in the second embodiment.

  In the intra prediction replacement in step S805, regardless of the data acquired in step S801, the prediction mode is fixed to a specific mode, and all the data is replaced with the corresponding prediction values for the color difference signal data. For example, the prediction mode is 8 × 8 DC prediction, and all of the color difference data is replaced with the DC prediction value from the intra prediction unit 710.

  In the case of inter prediction replacement in step S806, the color difference signal component data is replaced with the prediction signal sent from the inter prediction unit 713 regardless of the data acquired in step S801.

  When the color signal is replaced by the color difference signal replacement unit 716, the residuals of the color difference signals output from the differentiator 702 are all zero. Accordingly, even after the integer conversion in the integer converter 704, all the color difference signal data remains 0. For this reason, in the entropy encoding performed by the entropy encoder 705, since all data is 0, the bit corresponding to the color difference block of the coded block pattern is encoded with no data of the color difference signal component. Process. For this reason, a code corresponding to the color difference signal is not generated.

  In the present embodiment, as in the second embodiment, the level of the luminance signal is checked for the input image data, and if this level is outside the predetermined range, the value of the color difference signal is replaced using the prediction signal. That is, the luminance signal detection and the color difference signal replacement process are performed as processes in the previous stage of the main part of the encoding process (from the differencer 702 to the motion detection unit 714). For this reason, the function of the present invention can be added without changing the operation of the main part of the encoding process. In other words, the present invention can be realized as preprocessing even when an existing image encoding apparatus in which the main part of the encoding process is configured by hardware or the like is used.

  Also in this embodiment, as in the second embodiment, the luminance signal may be out of the predetermined range after decoding due to the influence of the quantization error. However, since the influence is generally limited to the level of quantization error, it remains the luminance signal level that makes it difficult to recognize the color signal. Therefore, even if the decoded color difference signal is significantly different from the color difference signal before encoding, almost no coding deterioration is felt.

  As described above, in the present embodiment, as in the second embodiment, the detection of the luminance signal and the processing for the color difference signal are performed as pre-coding processing. As a result, the present invention can be realized with almost no change to the existing image encoding apparatus. That is, almost no sign of the color difference signal is generated for the macroblock whose luminance signal level is in a range where the color cannot be recognized. As a result of performing such an encoding process, it is possible to reduce the amount of codes of the entire image data and to improve the encoding efficiency.

(Another embodiment according to the present invention)
Each unit constituting the image coding apparatus according to the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable recording medium recording the program are included in the present invention.

  In addition, the present invention can be implemented as a system, apparatus, method, program, storage medium, or the like, and can be applied to a system composed of a plurality of devices. Moreover, you may apply to the apparatus which consists of one apparatus.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowcharts shown in FIGS. 2, 4, 6, and 8) that executes each step in the above-described image encoding method is used as a system or apparatus. Directly or remotely. In addition, this includes a case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Various recording media can be used as a recording medium for supplying the program. For example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As another program supply method, a browser on a client computer is used to connect to an Internet home page. The computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from the homepage by downloading it to a recording medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. Let It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer performs part or all of the actual processing. Also, the functions of the above-described embodiments can be realized.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instructions of the program, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiment are also realized by the processing.

1 is a block diagram illustrating an exemplary configuration of an image encoding device according to a first embodiment, illustrating an embodiment of the present invention. 5 is a flowchart illustrating an example of a color signal processing procedure of the image encoding device performed in the first embodiment according to the embodiment of this invention. It is a block diagram which shows embodiment of this invention and shows the structural example of the image coding apparatus of 2nd Embodiment. It is a flowchart which shows embodiment of this invention and demonstrates an example of the color signal processing procedure of the image coding apparatus performed by 2nd Embodiment. It is a block diagram which shows embodiment of this invention and shows the structural example of the image coding apparatus of 3rd Embodiment. It is a flowchart which shows embodiment of this invention and demonstrates an example of the color signal processing procedure of the image coding apparatus performed by 3rd Embodiment. It is a block diagram which shows embodiment of this invention and shows the structural example of the image coding apparatus of 4th Embodiment. It is a flowchart which shows embodiment of this invention and demonstrates an example of the color signal processing procedure of the image coding apparatus performed by 4th Embodiment. It is a color difference conversion block block diagram. It is explanatory drawing about color difference space. It is a block diagram explaining the example of a structure of MPEG2 encoder. It is a figure explaining a 4: 2: 0 macroblock structure. It is explanatory drawing of intra DC prediction. It is explanatory drawing of inter prediction. It is explanatory drawing about coded block pattern. It is a block diagram explaining the structural example of the conventional H.264 encoder. It is explanatory drawing of intra 8x8 prediction.

Explanation of symbols

115 Luminance signal detection unit 315 of the first embodiment Luminance signal detection unit 316 of the second embodiment Color difference signal replacement unit 515 of the second embodiment Luminance signal detection unit 715 of the third embodiment Fourth embodiment Luminance signal detection unit 716 color difference signal replacement unit of the fourth embodiment

Claims (22)

An image encoding apparatus that decomposes image data composed of a luminance component and a color difference component into blocks each composed of a plurality of pixels, and performs an encoding process on each block,
Range detection means for detecting whether the value of the luminance component in the block unit is outside a predetermined range;
If the value of the luminance component in the block unit is outside the predetermined range as a result of detection by the range detection means, the code amount is the smallest for the color difference component in the block unit regardless of the component. An image encoding apparatus comprising: code assigning means for assigning codes.   The outside of the predetermined range means that the value of the luminance component is smaller than the first threshold value specified for the value of the luminance component, or the second threshold value that is larger than the first threshold value. The image coding apparatus according to claim 1, wherein the value of the luminance component is large. Encoding means for performing encoding by encoding the value of the luminance component in the block unit;
Decoding means for decoding the value of the luminance component in the block unit encoded by the encoding means,
2. The range detecting unit detects whether or not the value of a luminance component decoded by the decoding unit after being encoded by the encoding unit is outside a predetermined range. The image encoding device described in 1. When the value of the luminance component within the block unit is outside the predetermined range, and when the block outside the predetermined range is intra-processed, the DC component is equal to the DC prediction value, and the AC components are all 0. Encoded as
When the block is inter-processed, it has coding means for coding a bit string indicating the presence / absence of a code of a block unit in a state where there is no code for a bit indicating the presence / absence of a code of a color difference component The image encoding device according to claim 1.   If the value of the luminance component within the block unit of the luminance component of the input image data is outside the predetermined range as a result of detection by the range detection means, the code difference is replaced with the color difference component within the block unit. 5. The image coding apparatus according to claim 1, further comprising a color difference component replacement unit that replaces the data with the least generated data.   The color difference component replacement unit replaces all values of the color difference components in the block with a DC prediction value when a block outside the predetermined range is subjected to intra processing, and when the block is subjected to inter processing. 6. The image coding apparatus according to claim 5, wherein the color difference component in the block is replaced with the color difference component of the inter prediction destination. An image encoding apparatus that decomposes image data composed of a luminance component and a color difference component into blocks each composed of a plurality of pixels, and performs an encoding process on each block,
Encoding means for performing encoding by encoding the value of the luminance component in the block unit;
Decoding means for decoding a value of a luminance component in a block unit encoded by the encoding means;
Filter processing means for performing filter processing on the value of the luminance component decoded by the decoding means;
Range detection means for detecting whether the value of the luminance component filtered by the filter processing means is outside a predetermined range;
If the value of the luminance component in the block unit is outside the predetermined range as a result of detection by the range detection means, the code amount is the smallest for the color difference component in the block unit regardless of the component. An image encoding apparatus comprising: code assigning means for assigning codes.   When the value of the luminance component in the block unit is out of a predetermined range, the encoding means unsigns the bit indicating the presence / absence of the code of the color difference component in the bit string indicating the presence / absence of the code of the block unit. The image encoding apparatus according to claim 7, wherein a code to be assigned to a color difference component in the block unit is encoded as the state. An image encoding apparatus that decomposes image data composed of a luminance component and a color difference component into blocks each composed of a plurality of pixels, and performs an encoding process on each block,
Range detection means for detecting whether the value of the luminance component in the block unit is outside a predetermined range;
As a result of the detection by the range detection means, if the value of the luminance component within the block unit is outside the predetermined range, and if the block outside the predetermined range is subjected to intra processing, the block is predicted in a specific prediction mode. If all the values of the color difference components in the block are replaced with the prediction values of the prediction mode, and the block is inter-processed, the color difference components in the block are replaced with the color difference components of the inter prediction destination An image coding apparatus comprising: a color difference component replacement unit. An image encoding method for decomposing image data composed of a luminance component and a color difference component into blocks each composed of a plurality of pixels, and performing an encoding process for each block,
A range detection step of detecting whether the value of the luminance component in the block unit is outside a predetermined range;
If the value of the luminance component in the block unit is outside the predetermined range as a result of detection in the range detection step, the code amount is the smallest for the color difference component in the block unit regardless of the component. And a code assigning step for assigning a code.   The outside of the predetermined range means that the value of the luminance component is smaller than the first threshold value specified for the value of the luminance component, or the second threshold value that is larger than the first threshold value. The image encoding method according to claim 10, wherein the luminance component value is large. An encoding step of encoding by performing a quantization process on the value of the luminance component in the block unit;
A decoding step of decoding the value of the luminance component in the block unit encoded in the encoding step,
11. The range detecting step detects whether or not a luminance component value encoded in the encoding step and then decoded in the decoding step is outside a predetermined range. The image encoding method described in 1. When the value of the luminance component within the block unit is outside the predetermined range, and when the block outside the predetermined range is intra-processed, the DC component is equal to the DC prediction value, and the AC components are all 0. Encoded as
When the block is inter-processed, it has an encoding step of encoding a bit string indicating the presence / absence of a code of a block unit as a non-signed state with a bit indicating the presence / absence of a code of a color difference component The image encoding method according to claim 10.   As a result of the detection in the range detection step, when the value of the luminance component within the block unit of the luminance component of the input image data is outside the predetermined range, the code difference is replaced with the color difference component within the block unit. The image coding method according to claim 10, further comprising a color difference component replacement step of replacing the data with the least generated data.   The color difference component replacement step replaces all the values of the color difference components in the block with a DC prediction value when a block outside the predetermined range is intra-processed, and when the block is inter-processed The image coding method according to claim 14, wherein a color difference component in a block is replaced with a color difference component of an inter prediction destination. An image encoding method for decomposing image data composed of a luminance component and a color difference component into blocks each composed of a plurality of pixels, and performing an encoding process for each block,
An encoding step of encoding by performing a quantization process on the value of the luminance component in the block unit;
A decoding step of decoding the value of the luminance component in the block unit encoded in the encoding step;
A filtering process for performing a filtering process on the value of the luminance component decoded in the decoding process;
A range detection step for detecting whether or not the luminance component value filtered in the filtering step is outside a predetermined range;
If the value of the luminance component in the block unit is outside the predetermined range as a result of detection in the range detection step, the code amount is the smallest for the color difference component in the block unit regardless of the component. And a code assigning step for assigning a code.   In the encoding step, when the value of the luminance component in the block unit is outside a predetermined range, the bit indicating the presence / absence of the code of the block unit is unsigned for the bit string indicating the presence / absence of the code of the block unit. The image encoding method according to claim 16, wherein a code to be assigned to a color difference component in the block unit is encoded as the state. An image encoding method for decomposing image data composed of a luminance component and a color difference component into blocks each composed of a plurality of pixels, and performing an encoding process for each block,
A range detection step of detecting whether the value of the luminance component in the block unit is outside a predetermined range;
As a result of the detection in the range detection step, if the value of the luminance component within the block unit is out of the predetermined range, or if the block outside the predetermined range is subjected to intra processing, the block is predicted in a specific prediction mode. If all the values of the color difference components in the block are replaced with the prediction values of the prediction mode, and the block is inter-processed, the color difference components in the block are replaced with the color difference components of the inter prediction destination And a color difference component replacement step. A program that causes a computer to execute a process of decomposing image data including a luminance component and a color difference component into blocks each including a plurality of pixels and performing an encoding process on each block,
A range detection step of detecting whether the value of the luminance component in the block unit is outside a predetermined range;
If the value of the luminance component in the block unit is outside the predetermined range as a result of detection in the range detection step, the code amount is the smallest for the color difference component in the block unit regardless of the component. A program for causing a computer to execute a code assignment step of assigning a code. A program that causes a computer to execute a process of decomposing image data including a luminance component and a color difference component into blocks each including a plurality of pixels and performing an encoding process on each block,
An encoding step of encoding by performing a quantization process on the value of the luminance component in the block unit;
A decoding step of decoding the value of the luminance component in the block unit encoded in the encoding step;
A filtering process for performing a filtering process on the value of the luminance component decoded in the decoding process;
A range detection step for detecting whether or not the luminance component value filtered in the filtering step is outside a predetermined range;
If the value of the luminance component in the block unit is outside the predetermined range as a result of detection in the range detection step, the code amount is the smallest for the color difference component in the block unit regardless of the component. A program for causing a computer to execute a code assignment step of assigning a code. A program that causes a computer to execute a process of decomposing image data including a luminance component and a color difference component into blocks each including a plurality of pixels and performing an encoding process on each block,
A range detection step of detecting whether the value of the luminance component in the block unit is outside a predetermined range;
As a result of the detection in the range detection step, if the value of the luminance component within the block unit is out of the predetermined range, or if the block outside the predetermined range is subjected to intra processing, the block is predicted in a specific prediction mode. If all the values of the color difference components in the block are replaced with the prediction values of the prediction mode, and the block is inter-processed, the color difference components in the block are replaced with the color difference components of the inter prediction destination A program for causing a computer to execute a color difference component replacement step.   A computer-readable storage medium storing the program according to any one of claims 19 to 21.

Images