JP4109875B2 - Image encoding apparatus, image encoding method, program, and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image encoding device that encodes an image, an image decoding device that decodes an image based on code data including a code command, an image encoding method, an image decoding method, a program, and a storage medium.
[0002]
[Prior art]
Conventionally, when compressing image data, using the fact that pixels having the same pixel value in the horizontal direction and the vertical direction tend to be continuous, a position that has a high correlation with the position of interest, or a position immediately above or directly above. It is common to perform encoding with reference.
[0003]
In addition, when the image data to be compressed is image data that has been subjected to color reduction processing using a dither matrix, different operations are applied to adjacent pixels when performing color reduction processing. Rather, the correlation with the pixels separated by the period of the dither matrix used for the color reduction processing is high. Therefore, in such a case, when the period of the dither matrix used for the color reduction process is known, there is a method in which encoding is performed with reference to the left or upper position that is separated from the target position by the period of the dither matrix. is there.
[0004]
[Problems to be solved by the invention]
However, according to the above method, when the period of the image data is different from the period of the dither matrix, the correlation between the target position and the reference position is not so high, and thus there is a disadvantage that the compression cannot be performed efficiently. For example, such a problem may occur when the image data to be compressed is image data that has been subjected to color reduction processing after performing resolution conversion on an original image having a different resolution.
[0005]
The present invention has been made in view of the above problems, and an object of the present invention is to efficiently encode an image with a particularly short code.
[0006]
[Means for Solving the Problems]
In order to achieve the object of the present invention, for example, an image encoding apparatus of the present invention comprises the following arrangement.
[0007]
  That is,Pseudo halftone processing means for performing pseudo halftone processing on an image using a matrix of n rows and m columns;
  A first reference pixel that is separated from the encoding target pixel in the row direction by a distance n × a (a> 0) in the image subjected to the pseudo halftone process, and a distance m × b in the column direction from the encoding target pixel (B> 0) a reference means for referring to a second reference pixel separated according to a set reference order;
  When the reference pixel referred to by the reference means is effective for encoding the encoding target pixel, the encoding means for encoding the encoding target pixel using the reference pixel; Prepared,
  The reference order is the encoding of the previous pixel and the previous pixel in which the positional relationship between the first reference pixel and the second reference pixel and the encoding target pixel is encoded immediately before the encoding target pixel. Sometimes it is set to refer from the reference pixel that satisfies the positional relationship with the reference pixel used by the encoding means.It is characterized by that.
[0010]
In order to achieve the object of the present invention, for example, an image encoding method of the present invention comprises the following arrangement.
[0011]
  That is,A pseudo halftone processing step of performing pseudo halftone processing on an image using a matrix of n rows and m columns;
  A first reference pixel that is separated from the encoding target pixel in the row direction by a distance n × a (a> 0) in the image subjected to the pseudo halftone process, and a distance m × b in the column direction from the encoding target pixel (B> 0) a reference step of referring to the separated second reference pixel according to the set reference order;
  An encoding step of encoding the encoding target pixel using the reference pixel when the reference pixel referred in the reference step is effective for encoding the encoding target pixel; Prepared,
  The reference order is the encoding of the previous pixel and the previous pixel in which the positional relationship between the first reference pixel and the second reference pixel and the encoding target pixel is encoded immediately before the encoding target pixel. Sometimes it is set to refer from the reference pixel that satisfies the positional relationship with the reference pixel used by the encoding means.It is characterized by that.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to the accompanying drawings.
[0015]
[First Embodiment]
FIG. 1 is a diagram showing the relationship between each software group in the computer 1 that functions as an image encoding apparatus and the printer 6 in this embodiment.
[0016]
In the figure, reference numeral 1 denotes a computer having the basic configuration shown in FIG. FIG. 10 is a block diagram showing the basic configuration of the computer 1. In FIG. 10, reference numeral 1101 denotes a CPU that controls the entire apparatus using programs and data stored in the RAM 1102 and ROM 1103, and performs output control processing for outputting an image encoding process and a print command to the printer, which will be described later. And so on. A RAM 1102 includes an area for temporarily storing programs and data loaded from the external storage device 1104 and the storage medium drive 1109, and also includes a work area used when the CPU 101 executes various processes. Reference numeral 1103 denotes a ROM which stores a program for controlling the entire apparatus, setting data, and the like.
[0017]
Reference numeral 1104 denotes an external storage device such as a hard disk, which can store the following software group and data to be encoded as files. Reference numerals 1105 and 1106 denote a keyboard and a mouse, respectively. Various instructions can be input to the apparatus as a pointing device. A display device 1107 includes a CRT, a liquid crystal screen, and the like, and can display data to be encoded, an application GUI, and the like. Reference numeral 1108 denotes an image input device, which is configured by a device such as a scanner or a digital camera that can input an image as digital data to this device. The input image is output as a file to the external storage device 1104 or the RAM 1102. The
[0018]
Reference numeral 1109 denotes a storage medium drive, which reads a program or data from a storage medium such as a CD-ROM or a DVD-ROM and outputs the read program or data to the external storage device 1104. Note that the following software group and data to be encoded may be stored in the storage medium and supplied from the storage medium drive 1109 to this apparatus. Reference numeral 1110 denotes a USB or parallel port for connecting to a LAN or the Internet via an I / F (interface). In this embodiment, a parallel port is used to connect to a printer 6 described later. It is not limited. Reference numeral 1111 denotes a bus connecting the above-described units.
[0019]
Returning to FIG. 1, reference numeral 2 denotes an operating system that manages hardware included in the computer 1 and software such as an application 3, a printer driver 4, and a port driver 5. The application 3 is application software such as a word processor, and creates / prints a document in accordance with an instruction from the operator. A printer driver 4 receives a print command issued by the application 3 via the operating system 2 and converts the print command into a printer command interpretable by the printer 6. A port driver 5 receives the printer command converted by the printer driver 4 via the operating system 2 and transmits it to the printer 6 via the parallel port.
[0020]
Software groups such as the operating system 2, the application 3, the printer driver 4, and the port driver 5 are stored in the external storage device 1104 as described above. Reference numeral 6 denotes a printer, which performs printing in accordance with a printer command received from the port driver 5.
[0021]
FIG. 2 is a block diagram showing a basic configuration of the printer 6 functioning as an image decoding apparatus in the present embodiment. In the figure, reference numeral 11 denotes a parallel port which receives a printer command from the computer 1. A FIFO (First In First Out) memory 12 stores the encoded data received by the parallel port 11 and outputs the stored data to the decoding circuit 13 in the order of first-in first-out. The decoding circuit 13 decodes the code string data stored in the FIFO memory 12 and outputs it to the printer engine 14. The printer engine 14 is a laser beam printer engine, and performs printing according to the image data output from the decoding circuit 13 according to an instruction from the control circuit 15. The image data is output in frame sequential order for each color of cyan, magenta, yellow, and black. Reference numeral 15 denotes a control circuit, which is composed of, for example, a one-chip CPU, and controls the parallel port 11, the FIFO memory 12, the decoding circuit 13, and the printer engine 14.
[0022]
Hereinafter, the printing operation will be described.
[0023]
When the operator operates the application 3 using the keyboard 1105 or the mouse 1106 on the computer 1 side to generate print data and instructs to print it, the print command is sent from the application 3 to the printer driver 4 via the operating system 2. Passed. The printer driver 4 creates RGB image data composed of three colors of red, green, and blue based on the print command issued from the application 3, and then the RGB image data is composed of four colors of cyan, magenta, yellow, and black. Convert to CMYK image data. At the same time, a color reduction process is performed using a predetermined dither matrix. Then, the printer driver 3 generates encoded data from the created image data based on an encoding procedure to be described later, and outputs the encoded data together with a print control command that specifies the paper size, the line length of the bitmap data, the number of lines, and the like. . The port driver 5 transmits to the printer 6 a series of printer commands created by the printer driver 3 and including print control commands and encoded data.
[0024]
The control circuit 15 receives a printer command via the parallel port 11. If the received printer command is a print control command, it is held inside the control circuit 15 for print control. If the received printer command is encoded data, it is stored in the FIFO memory 12. Thereafter, when it is detected that the reception of a printer command constituting one page is completed by receiving a page end command or the like, the control circuit 15 instructs the printer engine 14 to start printing.
[0025]
When the start of printing is instructed, the printer engine 14 feeds paper from the paper feed cassette, and requests the decoding circuit 13 to output image data when the paper reaches a predetermined position. The decoding circuit 13 reads out the encoded data from the FIFO memory 12 in advance, stores the decoded image data in an internal buffer, and stores the decoded image data in the internal buffer when the printer engine 14 is requested to output the image data. The image data that has been saved is output. The decoding circuit 13 reads the subsequent encoded data from the FIFO memory 12 when the buffer for holding the image data is empty, decodes it, and holds it in the internal buffer. In this way, the encoded data is sequentially decoded and output as image data. When all the output of one page of image data is completed, printing is completed.
[0026]
Next, the codes generated by the printer driver 3 shown in FIG. 1 will be described with reference to the tables shown in FIGS.
[0027]
FIG. 3 is a diagram illustrating an example of an encoding table generated by the printer driver 3 illustrated in FIG. The code described in the present embodiment has a variable length in units of bits, and is represented by a bit string from 2 bits to 18 bits, for example. Similar to the Huffman code, each code is configured such that the code can be identified by examining sequentially from the top.
[0028]
In the present embodiment, two left reference positions and two upper reference positions are referred to at the time of encoding. For example, the left reference position is matched with the characteristics of the dither matrix used at the time of color reduction processing. Are the positions one byte left and four bytes left of the target position, and the upper reference position is four lines above the target position, two lines, and two bytes left.
[0029]
As shown in FIG. 3, when the bit string of the code starts with “1”, it is a COPY UP1 command. This command is followed by a code indicating a length, which will be described later, and instructs to copy a byte string having a length indicated by the subsequent code from a predetermined high-order upper reference position.
[0030]
When the code bit string starts with “011”, it is a COPY UP2 command. This command is followed by a code indicating the length to be described later, and copies a byte sequence of the length indicated by the subsequent code from a predetermined low-order upper reference position. To replace the upper reference position.
[0031]
If the bit string of the code starts with “001”, it is a RAW command. This command is followed by 8-bit data indicating raw data, and designates 1-byte data having the value of the subsequent 8-bit data.
[0032]
When the code bit string starts with “010”, it is a COPY LEFT1 command. This command is followed by a code indicating a length to be described later, and instructs to copy a byte string having a length indicated by the subsequent code from a predetermined high-order left reference position.
[0033]
When the code bit string starts with “0001”, it is a COPY LEFT2 command. This command is followed by a code indicating the length, which will be described later, copying a byte sequence of the length indicated by the subsequent code from a predetermined low-order left reference position, Instructs to replace the left reference position of the rank.
[0034]
When the bit string of the code is “0000”, it is an EOB command and instructs the end of the code block.
[0035]
If the data matches at the low-order reference position, there is a high possibility that the data will match at the reference position. Therefore, when a longer code that identifies a lower-order reference position is output, if the rank of the reference position is raised and then identified by a shorter code, the data matches after that at the reference position. In this case, the length of the output code is shortened. Therefore, by executing the COPY UP2 command and the COPY LEFT2 command, the high-order reference position and the low-order reference position are switched, and the length of the code to be output in the future is shortened.
[0036]
FIG. 4 is an example of an encoding table of codes indicating lengths following the COPY UP1 command, COPY UP2 command, COPY LEFT1 command, or COPY LEFT2 command shown in FIG.
[0037]
As shown in FIG. 4, when the bit string of the code is “1”, the length of 1 byte is indicated.
[0038]
When the bit string of the code starts with “01”, 1-bit data follows, and indicates a length obtained by adding 2 to the subsequent 1-bit data, that is, a length of 2 bytes or 3 bytes.
[0039]
When the code bit string starts with “001”, 2 bits of data follow, and a length obtained by adding 4 to the subsequent 2 bits of data, that is, a length from 4 bytes to 7 bytes is indicated.
[0040]
When the code bit string starts with “0001”, 3 bits of data follow, and a length obtained by adding 8 to the subsequent 3 bits of data, that is, a length from 8 bytes to 15 bytes is indicated.
[0041]
When the bit string of the code starts with “00001”, 4-bit data follows, and a length obtained by adding 16 to the subsequent 4-bit data, that is, a length from 16 bytes to 31 bytes is indicated.
[0042]
When the bit string of the code starts with “000001”, 5-bit data follows, and a length obtained by adding 32 to the subsequent 5-bit data, that is, a length from 32 bytes to 63 bytes is indicated.
[0043]
When the code bit string starts with “0000001”, 6-bit data follows, and the length obtained by adding 64 to the subsequent 6-bit data, that is, the length from 64 bytes to 127 bytes is indicated.
[0044]
When the bit string of the code starts with “0000000”, 7-bit data follows, and indicates a length obtained by adding 128 to the subsequent 7-bit data, that is, a length from 128 bytes to 255 bytes.
[0045]
For these codes, the appearance frequency of each command is obtained in advance with a large number of image data, and as with the Huffman code, a short code is assigned to a command with a high appearance frequency, and a relatively long code is assigned to a command with a low appearance frequency. By assigning, the compression rate can be increased.
[0046]
Next, with reference to FIGS. 5A and 5B, the encoding process will be described with an example. FIG. 5A shows the image data to be encoded, and FIG. 5B shows the encoded data. As shown in FIG. 5A, 10 bytes of image data (attention data) 00, 00, 12, 34, 56, 78, 00, BC, DE, 00 are arranged in the bottom row from the left. Image data 12, 34, 56, 78, 9A, BC, DE, 00, 00, 00 (reference data) are arranged on the second line from the left. The image data that is currently being encoded or decoded is the bottom row, and at this point, the high-order left reference position is 1 byte to the left (that is, the low-order left reference position is 4 bytes to the left), It is assumed that the lower reference upper reference position is on the second line and two bytes to the left (that is, the higher priority upper reference position is on the fourth line).
[0047]
Here, the first byte 00 in the bottom row can be encoded into a bit string 001 00000000, that is, a RAW command indicating the raw data 00.
[0048]
Further, the next byte 00 can be encoded into a COPY LEFT1 command that copies the bit string 010 1, that is, the length of 1 byte, from the high-order left reference position, that is, the position 1 byte left.
[0049]
The next byte sequence 12, 34, 56, 78 is a bit sequence 011 001 00, that is, a COPY UP2 command for copying the length of 4 bytes from the lower-order upper reference position, that is, 2 lines and 2 bytes to the left. Can be encoded. As a result, the order of the upper reference position is switched, and the subsequent COPY UP1 command is located two lines and two bytes left from the lower order to the higher order, and the COPY UP2 command is changed from the higher order to the lower order. Refer to each position on the line.
[0050]
The next byte 00 can again be encoded into a bit string 001 00000000, ie, a RAW command indicating raw data 00.
[0051]
The next byte string BC, DE, 00 is a bit string 1 01 1, which is a code for a COPY UP1 command to copy the length of 3 bytes from the upper reference position in the highest order, that is, 2 lines and 2 bytes to the left. Can be
[0052]
As described above, the image data can be encoded. Next, details of processing of the printer driver 4 will be described with reference to a flowchart shown in FIG. FIG. 6 is a flowchart of processing performed by the printer driver 4. The program according to this flowchart is stored as the printer driver 4 in the external storage device 1104 or a storage medium as described above, and is read out and executed by the CPU 101 (in the case of a storage medium, by the storage medium drive 1109) into the RAM 1102. .
[0053]
When the printer driver 4 is called from the operating system 2, it is first determined in step S5 whether or not the call type is a drawing command. If the call type is a drawing command, a drawing process is performed in step S6, and the process ends. Specifically, a character, figure, bitmap, or the like designated by the application 3 via the operating system 2 is converted into an 8-bit image of each color using red, green, and blue, and recorded in the RAM 1102. To do.
[0054]
If the call type is not a drawing command in step S5, it is determined in step S7 whether the call type is a page end command. If the call type is a page end command, color conversion processing is performed in step S8. Specifically, an 8-bit image using the three colors red, green, and blue recorded in the RAM 1102 in step S6 is converted into four colors of cyan, magenta, yellow, and black using a predetermined dither matrix. For example, each image is converted into a 4-bit image. The converted image is also stored in the RAM 1102.
[0055]
Next, in step S9, a print condition designation command, specifically a command for designating conditions necessary for printing such as paper size, paper feed cassette, resolution, number of gradations, number of bytes of one line, number of lines of one page, etc. Is output.
[0056]
Next, each processing from step S10 to step S14 is performed for each color of cyan, magenta, yellow, and black, and an image data command for each color is output. First, in step S10, the compression parameter corresponding to the dither matrix used in step S8, that is, the position referenced by the COPY UP command and the COPYLEFT command used at the time of encoding (high-order upper reference position, lower-order upper reference). Position, high-order left reference position, and low-order left reference position). In step S11, the image data is encoded in accordance with an encoding procedure described later. At this time, encoding is performed using the positions referred to by the COPY UP command and the COPY LEFT command specified by the compression parameter output in step S10. Details will be described later.
[0057]
In step S12, an image data command header that specifies the size and the number of lines of the image data encoded in step S11 is output. In step S13, the image data encoded in step S11 is output. Next, in step S14, it is determined whether or not the processing for each of the cyan, magenta, yellow, and black planes has been completed. If the processing for each of the cyan, magenta, yellow, and black planes has not been completed, the process returns to step S10 to change the color and perform the processing for the next plane. When the processing for each of the cyan, magenta, yellow, and black planes is completed in this way, the process proceeds from step S14 to step S15, and a page break command for designating the end of the page is output to end the process.
[0058]
If the call type is not a page end command in step S7, other processing corresponding to the call type is performed in step S16, for example, a process corresponding to a page start command or a printer capability inquiry command. finish.
[0059]
Next, the encoding process in step S11 will be described with reference to FIG. 7 showing a flowchart of the process. A program according to this flowchart is incorporated in the printer driver 4 as a subroutine of the flowchart.
[0060]
First, in step S19, the higher-order upper reference position, the lower-order upper reference position, the higher-order left reference position, and the lower-order left reference position are respectively set to predetermined initial values, that is, the compression parameters obtained in step S10. Set according to. In step S20, the current position, that is, the position of the image to be encoded is set at the left end of the first line of the image.
[0061]
Next, in step S21, it is determined whether or not the higher-order upper reference position corresponding to the current position refers to valid image data. If the high-order upper reference position refers to valid image data, in step S22, the length that matches the higher-order upper reference position is set to a byte sequence starting from the current position, It is obtained by comparing byte sequences starting from the upper reference position. At this time, if the end of the line is reached or the length reaches 255 bytes, the processing is aborted. Next, in step S23, it is determined whether or not the length that is obtained in step S22 and matches the upper reference position in the higher order is zero. If it is not 0, it can be encoded into a COPY UP1 command. In step S24, a COPY UP1 command, that is, a code indicating the code 1 and the number of bytes following it (the length obtained in step S22) is output, and the process is performed. Proceed to S40.
[0062]
On the other hand, if it is determined in step S21 that the high-order upper reference position is invalid, it is determined in step S23 that the length that matches the high-order upper reference position obtained in step S22 is zero. If so, in step S25, it is determined whether or not the higher-order left reference position corresponding to the current position refers to valid image data. If the high-order left reference position refers to valid image data, in step S26, the length matching the high-order left reference position is set to a byte string starting from the current position, and the high-order left reference position. It is obtained by comparing byte sequences starting from the left reference position. At this time, if the end of the line is reached or the length reaches 255 bytes, the processing is aborted. Next, in step S27, it is determined whether or not the length that is obtained in step S26 and matches the high-order left reference position is zero. If it is not 0, it can be encoded into a COPY LEFT1 command. Therefore, in step S28, a COPY LEFT1 command, that is, a code indicating the code 010 and the number of subsequent bytes (the length obtained in step S26) is output, and the processing is performed. Proceed to S40.
[0063]
If it is determined in step S25 that the high-order left reference position is invalid, it is determined in step S27 that the length corresponding to the high-order left reference position obtained in step S26 is zero. In any case, in step S29, it is determined whether or not the lower-reference upper reference position corresponding to the current position refers to valid image data. If the lower-order upper reference position refers to valid image data, in step S30, the length matching the lower-order upper reference position is set to a byte sequence starting from the current position, and the lower-order upper reference position. It is obtained by comparing byte sequences starting from the upper reference position. At this time, if the end of the line is reached or the length reaches 255 bytes, the processing is aborted. Next, in step S31, it is determined whether or not the length obtained in step S30 and the length matching the lower reference upper reference position is zero. If it is not 0, it can be encoded into a COPY UP2 command. In step S32, a COPY UP2 command, that is, a code indicating the code 011 and the number of bytes subsequent thereto (the length obtained in step S30) is output, In step S33, the upper reference position in the higher order and the upper reference position in the lower order are exchanged, and the process proceeds to step S40.
[0064]
When it is determined in step S29 that the lower-order upper reference position is invalid, and in step S31, it is determined that the length that is obtained in step S30 and matches the lower-order upper reference position is zero. In any case, in step S34, it is determined whether or not the low-order left reference position corresponding to the current position refers to valid image data. If the low-order left reference position refers to valid image data, in step S35, the length matching the low-order left reference position is set to a byte sequence starting from the current position, and the low-order left reference position. It is obtained by comparing byte sequences starting from the left reference position. At this time, if the end of the line is reached or the length reaches 255 bytes, the processing is aborted. Next, in step S36, it is determined whether or not the length that matches the low-order left reference position obtained in step S35 is zero. If it is not 0, it can be encoded into a COPY LEFT2 command. Therefore, in step S37, a COPY LEFT2 command, that is, a code indicating the code 0001 and the number of subsequent bytes (the length obtained in step S35) is output. In S38, the high-order left reference position and the low-order left reference position are switched, and the process proceeds to Step S40.
[0065]
When it is determined in step S34 that the low-order left reference position is invalid, and in step S36, it is determined that the length that matches the low-order left reference position obtained in step S35 is zero. In either case, in step S39, the RAW command, that is, the code 001 and the subsequent 1-byte data at the current position are output, and the process proceeds to step S40.
[0066]
In step S40, the current position is advanced by the number of bytes processed by COPY UP1, COPY UP2, COPY LEFT1, COPY LEFT2, or the RAW command. Next, in step S41, it is determined whether or not all image data has been processed. If all the image data has not been processed, the process returns to step S21 to continue encoding. When all the image data has been processed, an EOB command, that is, a code 0000 is output in step S42, and then the code is aligned on a byte boundary in step S43. Specifically, if the total number of bits of the output code is not an integer multiple of 8, bit 0 is output until it reaches an integer multiple of 8. When the encoding process is completed in this way, the process returns.
[0067]
Next, details of the circuit will be described with reference to FIG. 8 showing the configuration of the decoding circuit 13 shown in FIG. FIG. 8 is a block diagram showing a basic configuration of the decoding circuit 13 shown in FIG.
[0068]
In FIG. 8, the input buffer 21 stores the code data read from the FIFO memory 12. The input buffer 21 can store at least 4 bytes of data, and when the buffer is empty and there is data in the FIFO memory 12, the data is read from the FIFO memory 12 and stored. The input buffer 21 also discards the processed data that is no longer necessary when the number of processed bits held in the bit counter 23 is 8 or more.
[0069]
The first selector 22 is, for example, 18 sets of 8-input selectors, and the command decode circuit 24 processes the code data stored in the input buffer 21 according to the number of processed bits indicated by the bit counter 23. Align the start position of the command necessary for this. This is necessary because the input buffer 21 holds data in units of bytes, whereas the command is variable-length data in units of bits, so there are eight start positions.
[0070]
The bit counter 23 stores the number of processed bits in the code data stored in the input buffer 21. The bit counter 23 also updates the value stored in the bit counter by adding the number of bits of the command output from the command decoding circuit 24. The bit counter 23 also subtracts the number of discarded bits when the input buffer discards the processed data. The bit counter 23 also receives an EOB signal from the command decode circuit 24 when the command decode circuit 24 decodes the EOB command, and performs byte boundary alignment processing. Specifically, if the lower 3 bits of the bit counter are all 0, nothing is done. Otherwise, 8 is added and the lower 3 bits are cleared.
[0071]
The command decode circuit 24 is constituted by, for example, a read-only memory or wired logic, decodes the code data stored in the input buffer 21 that has been aligned by the first selector 22, and the decoded command is an EOB command. Is the bit counter 23, the upper priority FF 29 and the left priority FF 30, and if the decoded command is a COPY UP1 command or a COPY UP2 command, the second selector 25 and the third selector 26 are decoded, and the decoded command is a COPY LEFT1 command. Alternatively, a signal is output to the fourth selector 27 and the fifth selector 28 in the case of a COPY LEFT2 command, and to the raw data output circuit 36 if the decoded command is a RAW command. The command decode circuit 24 also decodes and outputs the number of bytes indicated by the code when the COPY UP1, COPY UP2, COPY LEFT1, or COPY LEFT2 command is decoded, and when the RAW command is decoded, the 8 bits indicated by the code. Data is also decoded and output.
[0072]
Reference numeral 25 denotes a second selector. When the upper priority FF 29 holds 0, a signal output when the command decode circuit 24 decodes the COPY UP1 command, and when the upper priority FF 29 holds 1 Outputs a signal output when the command decode circuit 24 decodes the COPY UP2 command.
[0073]
Reference numeral 26 denotes a third selector. When the upper priority FF 29 holds 0, a signal output when the command decode circuit 24 decodes the COPY UP2 command, and when the upper priority FF 29 holds 1 Outputs a signal output when the command decode circuit 24 decodes the COPY UP1 command.
[0074]
Reference numeral 27 denotes a fourth selector. When the left priority FF 30 holds 0, a signal output when the command decode circuit 24 decodes the COPY LEFT1 command, and when the left priority FF 30 holds 1 Outputs a signal output when the command decode circuit 24 decodes the COPY LEFT2 command.
[0075]
Reference numeral 28 denotes a fifth selector. When the left priority FF 30 holds 0, a signal indicating that the command decode circuit 24 has decoded the COPY LEFT2 command, and when the left priority FF 30 holds 1, The command decode circuit 24 outputs a signal indicating that the COPY LEFT1 command has been decoded.
[0076]
Reference numeral 29 denotes an upper priority FF, which holds a value indicating which of the first upper copying circuit 31 or the second upper copying circuit 32 has priority. The upper priority FF 29 also inverts the value held when the command decode circuit 24 decodes the COPY UP2 command.
[0077]
Reference numeral 30 denotes a left priority FF, which holds a value indicating which of the first left copying circuit 33 or the second left copying circuit 34 has priority. The left priority FF 30 also inverts the value held when the command decode circuit 24 decodes the COPY LEFT2 command.
[0078]
Reference numeral 31 denotes a first upper copying circuit which receives the number of bytes to be copied when receiving a signal from the second selector 25 and reads data from the line buffer 35 in accordance with the received number of bytes. Repeatedly output the read data.
[0079]
Reference numeral 32 denotes a second upper copying circuit which receives the number of bytes to be copied when receiving a signal from the third selector 26 and reads data from the line buffer 35 according to the received number of bytes. Repeatedly output the read data.
[0080]
Reference numeral 33 denotes a first left copying circuit which receives the number of bytes to be copied when receiving a signal from the fourth selector 27 and reads data from the line buffer 35 in accordance with the received number of bytes. Repeatedly output the read data.
[0081]
Reference numeral 34 denotes a second left copying circuit which receives the number of bytes to be copied when receiving a signal from the fifth selector 28 and reads data from the line buffer 35 according to the received number of bytes. Repeatedly output the read data.
[0082]
Reference numeral 35 denotes a line buffer, which operates as a ring memory that holds decoded data of a plurality of lines. The first upper copying circuit 31, the second upper copying circuit 32, the first left copying circuit 33, or the second left copying circuit. The data stored in the address output from the copying circuit 34 is output, and the decoded data is stored in the address output from the current address register 37.
[0083]
A raw data output circuit 36 receives 8-bit data indicating raw data that is simultaneously output when the command decode circuit 24 decodes the RAW command, and outputs the received data.
[0084]
Reference numeral 37 denotes a current address register, which outputs an address indicating the position of data currently being decoded, and counts up every time the decoded data is stored in the line buffer 35.
[0085]
The first upper copying circuit 31, the second upper copying circuit 32, the first left copying circuit 33, and the second left copying circuit 34 include a first upper copying position, a second upper copying position, Addresses respectively indicating the first left copy position and the second left copy position are held, and are counted up in the same manner every time the current address register 37 is counted up.
[0086]
When the command decode circuit 24 decodes the COPY UP1 command, it decodes the subsequent count and outputs a signal to the second selector 25 and the third selector 26. A signal is output from either the second selector 25 or the third selector 26 according to the value held by the upper priority FF 29, and the first upper copying circuit 31 or the second upper copying circuit is output according to the signal. Any one of 32 operates.
[0087]
For example, if the value held by the upper priority FF 29 is 0, when the COPY UP1 command is decoded, the second selector 25 outputs a signal to the first upper copying circuit 31, and the third selector 26 outputs the signal. Do not output. The first upper copying circuit 31 outputs an address indicating the first upper copying position held therein to the line buffer 35, reads the data of the first upper copying position stored in the line buffer 35, and reads the data. The data is output to the printer engine 14 as decoded data. The current address register 37 outputs an address indicating the current position, and the line buffer 35 stores the decoded data at that address. Next, addresses indicating the first upper copy position respectively held in the first upper copy circuit 31, the second upper copy circuit 32, the first left copy circuit 33 and the second left copy circuit 34. The address indicating the second upper copy position, the address indicating the first left copy position and the address indicating the second left copy position, and the address indicating the current position held by the current address register 37 are counted up. This operation is repeated for the specified number of bytes.
[0088]
When the command decode circuit 24 decodes the COPY UP2 command, it decodes the subsequent count and outputs a signal to the second selector 25 and the third selector 26. A signal is output from either the second selector 25 or the third selector 26 according to the value held by the upper priority FF 29, and the first upper copying circuit 31 or the second upper copying circuit 32 is output according to the signal. Either one works.
[0089]
For example, if the value held by the upper priority FF 29 is 0, when the COPY UP2 command is decoded, the third selector 26 outputs a signal to the second upper copying circuit 32, and the second selector 25 outputs the signal. Do not output. The second upper copying circuit 32 operates in the same manner as the operation of the first upper copying circuit 31 described above. However, since the value held in the upper priority FF 29 is inverted to 1, the subsequent COPY UP1 command is the first one. The second upper reference position and the COPY UP2 command correspond to the first upper reference position, respectively.
[0090]
Even when the command decode circuit 24 decodes the COPY LEFT1 command and the COPY LEFT2 command, it operates in the same manner as the operations of the COPY UP1 command and the COPY UP2 command.
[0091]
When the command decode circuit 24 decodes the RAW command, the subsequent 8-bit data is decoded and a signal is output to the raw data output circuit 36. The raw data output circuit 36 outputs the received 8-bit data as it is to the printer engine 14 as decoded data. The current address register 37 outputs an address indicating the current position, and the line buffer 35 stores the decoded data at that address. Next, addresses indicating the first upper copy position respectively held in the first upper copy circuit 31, the second upper copy circuit 32, the first left copy circuit 33 and the second left copy circuit 34. The address indicating the second upper copy position, the address indicating the first left copy position and the address indicating the second left copy position, and the address indicating the current position held by the current address register 37 are counted up.
[0092]
When the command decode circuit 24 decodes the EOB command, the bit counter 23 performs the byte boundary alignment processing as described above, and the upper priority FF 29 and the left priority FF 30 are initialized to initial values, for example, 0.
[0093]
Addresses indicating the first upper copy positions respectively held in the first upper copy circuit 31, the second upper copy circuit 32, the first left copy circuit 33, and the second left copy circuit 34. The address indicating the second upper copy position, the address indicating the first left copy position, the address indicating the second left copy position, and the address indicating the current position held by the current address register 37 are previously set in the control circuit. 15, the initial value based on the position designated by the compression parameter designation command is set.
[0094]
Since the line buffer 35 operates as a ring memory, it is held inside the first upper copying circuit 31, the second upper copying circuit 32, the first left copying circuit 33, and the second left copying circuit 34, respectively. Held in the address indicating the first upper copying position, the address indicating the second upper copying position, the address indicating the first left copying position and the address indicating the second left copying position, or the current address register 37. When the address indicating the current position is the last address of the line buffer 35, the first address of the line buffer 35 is stored by wrapping around when counting up.
[0095]
From the above description, when a reference position encoded to a longer code is referred to by the image encoding apparatus and the image decoding apparatus according to the present embodiment, the reference position and the reference are interchanged, and then the reference is performed. Since a shorter code can be encoded when the position is referenced, compression can be performed efficiently regardless of the data cycle.
[0096]
In addition, when the period of the image data and the period of the dither matrix are different, there is a tendency that the correlation between the position near the position of interest and the position where the calculation close to the calculation applied at the position of interest is applied during the color reduction process is high . Such positions are limited to a small number of positions and can be determined by examining the dither matrix in advance or by taking statistics using various image data in advance. By selecting in advance a plurality of positions as reference positions from positions separated by a period, it is possible to efficiently encode regardless of the period of the image data.
[0097]
Also, the cycle of image data tends to be constant over a wide range. For this reason, when data matches at a low-order reference position, there is a high possibility that data will match at that reference position. Therefore, when a longer code for identifying a lower-order reference position is output, the rank of the reference position is increased, and thereafter the data is identified at the reference position by being identified by a shorter code. In this case, since the output code becomes shorter, the encoding can be performed more efficiently than the case where the order is not changed.
[0098]
[Second Embodiment]
In the above-described embodiment, decoding is performed by hardware. However, instead of this, decoding may be performed by software.
[0099]
In the above-described embodiment, the unit data size of encoding is 1 byte, but it may be another size, for example, 1 pixel or 2 bytes instead.
[0100]
In the above-described embodiment, the priority order of two reference positions is switched. Alternatively, the priority order of three or more reference positions may be switched.
[0101]
[Other Embodiments]
An object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus Needless to say, this can also be achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.
[0102]
Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.
[0103]
【The invention's effect】
As described above, according to the present invention, an image can be efficiently encoded with a particularly short code.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a relationship between a software group and a printer 6 in a computer 1 that functions as an image encoding device according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a basic configuration of a printer 6 that functions as an image decoding apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of an encoding table generated by the printer driver 3 illustrated in FIG. 1;
4 is a diagram illustrating an example of a coding table of codes indicating lengths subsequent to the COPY UP1 command, the COPY UP2 command, the COPY LEFT1 command, or the COPY LEFT2 command illustrated in FIG. 3;
5A is a diagram showing image data to be encoded, and FIG. 5B is a diagram showing encoded data.
FIG. 6 is a flowchart of processing performed by the printer driver 4;
FIG. 7 is a flowchart of the encoding process in step S11.
8 is a block diagram showing a basic configuration of a decoding circuit 13 shown in FIG.
FIG. 9 is a block diagram showing a basic configuration of a computer 1;

Claims (5)

Pseudo halftone processing means for performing pseudo halftone processing on an image using a matrix of n rows and m columns;
A first reference pixel that is separated from the encoding target pixel in the row direction by a distance n × a (a> 0) in the image subjected to the pseudo halftone process, and a distance m × b in the column direction from the encoding target pixel (B> 0) a reference means for referring to a second reference pixel separated according to a set reference order;
When the reference pixel referred to by the reference means is effective for encoding the encoding target pixel, the encoding means for encoding the encoding target pixel using the reference pixel; Prepared,
The reference order is the encoding of the previous pixel and the previous pixel in which the positional relationship between the first reference pixel and the second reference pixel and the encoding target pixel is encoded immediately before the encoding target pixel. sometimes the image coding apparatus according to the set, wherein Rukoto to refer to the reference pixels that satisfy the positional relationship between the reference pixel said encoding means are used. The first reference pixels are a plurality of reference pixels corresponding to different a respective said second reference pixels, to claim 1, wherein the plurality of reference pixels der Rukoto corresponding to different b respectively The image encoding device described. A pseudo halftone processing step of performing pseudo halftone processing on an image using a matrix of n rows and m columns;
A first reference pixel that is separated from the encoding target pixel in the row direction by a distance n × a (a> 0) in the image subjected to the pseudo halftone process, and a distance m × b in the column direction from the encoding target pixel (B> 0) a reference step of referring to the separated second reference pixel according to the set reference order;
An encoding step of encoding the encoding target pixel using the reference pixel when the reference pixel referred in the reference step is effective for encoding the encoding target pixel; Prepared,
The reference order is the encoding of the previous pixel and the previous pixel in which the positional relationship between the first reference pixel and the second reference pixel and the encoding target pixel is encoded immediately before the encoding target pixel. set the image coding method comprising Rukoto to refer to the reference pixels at satisfying the positional relationship between the reference pixel said encoding means are used. Computer program for executing the image encoding method according to claim 3 on a computer. And characterized by storing a computer program according to claim 4, a computer-readable storage medium.

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