JP2011019095A - Image processor and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor performing compression encoding processing for an image at a higher speed.SOLUTION: A simple prediction processing portion 410 determines whether a pixel value is in agreement for a sequence composed of a pixel of interest and peripheral pixels a, b, and c around the pixel of interest at lease in one of the longitudinal direction and the lateral direction, respectively. If it is determined that the pixel value is in agreement for every sequence in the longitudinal direction or the lateral direction, a run-length-generation processing portion 405 generates a run-length, under the condition that a prediction error to the pixel of interest is 0. On the other hand, if it is determined that a sequence with a mismatched pixel value exists in the longitudinal direction and a sequence with a mismatched pixel value exists in the lateral direction, a prediction processing portion 403 predicts a pixel value of the pixel of interest using the LOCO-I system or the Paeth system. A prediction error processing portion 404 calculates a prediction error. The run-length-generation processing portion 405 generates the run-length, based on the prediction error.

Description

  The present invention relates to an image processing apparatus and an image processing method for compressing and encoding image data.

  In an image forming apparatus such as a printer, input image data is temporarily stored in a memory, and the image data stored in the memory is read at a predetermined timing to perform a printing operation. In this case, if the image data is stored in the memory as it is, a large-capacity memory is required and the cost of the apparatus increases. Therefore, generally, input image data is compression-encoded and stored in a memory.

  In this printer apparatus or the like, compression encoding using predictive encoding is generally used. Predictive coding uses the property that the correlation between adjacent pixels is high in an image, predicts the pixel value of a target pixel to be encoded from the pixel values of the encoded pixels, and predicts the predicted value and the target pixel. The difference from the actual pixel value is encoded by entropy encoding.

  As a method conventionally used for this predictive coding, a plane prediction method, a Paeth method, a LOCO-I (LOw COmplexity Lossless Compression for Images) method, and the like are known. The plane prediction method is adopted in a lossless encoding mode of JPEG (Joint Photographic Experts Group). The Paeth method is disclosed in Alan W. It is a prediction method devised by Mr. Paeth and is adopted in PNG (Portable Network Graphics) which is an internationally standardized lossless compression method. The Paeth method is described in “Paeth, A.W.,“ Image File Compression Made Easy ”, Graphics Gems II, James Arvo, editor. Academic Press, San Diego, 1991”. The LOCO-I system is adopted in JPEG-LS (Joint Photographic Experts Group-LS), which is an internationally standardized compression system. The LOCO-I system is described in “M. J. Weinberger,“ LOCO-I: A Low Complexity, Context-Based, Lossless Image Compression Algorithm ”Proc. IEEE Data Compression conference (DCC), snowbird, Utah”.

  Among these prediction methods, the LOCO-I method and the Paeth method have a larger amount of processing for each pixel than the planar prediction, but the prediction error of the prediction value with respect to the pixel value of the target pixel is small, and higher accuracy. It is known that accurate prediction is possible.

  In Patent Document 1, when a prediction error obtained by predicting a target pixel from surrounding pixels is Huffman-coded, the prediction error values are classified into a plurality of groups within the range of the values, and are numerical values indicating the rank within the classification. A technique is disclosed in which a group value and an additional bit value are converted into a certain additional bit and Huffman encoded.

  Patent Document 2 discloses a plurality of prediction units and prediction error calculation units, a selection unit that selects them, and an encoding unit that encodes the prediction error selected by the selection unit and the identification numbers of the plurality of prediction units. Is disclosed. In Patent Document 2, the length predicted by a plurality of prediction units is encoded by run length, and when the prediction is not correct, the prediction error obtained by the prediction error calculation unit is encoded.

  Furthermore, Patent Document 3 describes a technique for predicting the pixel value of a target pixel using the first and second prediction methods. That is, in Patent Document 3, first, the pixel value of the target pixel is predicted using the first prediction method, and when the predicted value matches the pixel value of the target pixel, an ID indicating the first prediction method is set. If it is added to the code and does not match, the pixel value of the pixel of interest is predicted by the second prediction method. When the predicted value according to the second prediction method matches the pixel value of the target pixel, an ID indicating the second prediction method is added to the code. If the prediction values predicted by the first and second prediction methods do not match the pixel value of the target pixel, an ID indicating a mismatch with respect to the prediction method with the smaller prediction error is added to the code. The prediction error is encoded.

  Incidentally, in a printer apparatus or the like, it is necessary to perform image processing for printing in accordance with the printing speed of the print engine. In order to cope with an increase in printing speed, it is necessary to increase the image compression rate and increase the processing speed required for image compression encoding. That is, if the processing speed of image compression encoding is slower than the printing speed of the print engine, good print quality cannot be obtained. Therefore, there is a need for a faster image compression encoding method.

  JPEG's lossless encoding mode, known as a lossless compression method for multi-valued images, creates prediction error statistics with seven prediction formulas, selects one prediction formula that gives the best results, and is selected. The image data is encoded using the prediction formula. However, in this lossless encoding mode of JPEG, in order to create a prediction error statistic with each of seven prediction formulas for one image, a two-pass method for processing a multi-valued image twice is used, and the processing time is reduced. There was a problem that it took a lot.

  Further, according to Patent Document 2 described above, since a plurality of prediction processes are performed by a plurality of prediction units to obtain a prediction error, a large amount of processing is required, and even in this case, it takes a long processing time. There was a point.

  Further, according to Patent Document 3 described above, since the prediction error is obtained after trying at least two prediction methods, a large amount of processing is required and a long processing time is required. It was.

  Furthermore, in Patent Document 1 described above, a prediction error is obtained for each pixel for each pixel of the input image, and Huffman coding is performed. That is, according to Patent Document 1, it is necessary to perform prediction processing for each pixel using the above-described planar prediction method, Paeth method, LOCO-I method, and the like. Therefore, there is a problem that it is difficult to increase the processing speed.

  The present invention has been made in view of the above, and an object of the present invention is to provide an image processing apparatus and an image processing method capable of performing image compression encoding processing at higher speed.

  In order to solve the above-described problems and achieve the object, the present invention is an image processing apparatus that compresses and encodes multi-valued image data, and includes a vertical direction of an image of a target pixel and peripheral pixels of the target pixel, and First prediction means for determining whether or not a prediction error value, which is a difference between a pixel value of a target pixel and a predicted value with respect to the pixel value of the target pixel, is 0 based on at least one correlation in the horizontal direction; When the prediction error value is determined not to be 0 by the first prediction unit, the prediction value for the pixel value of the target pixel is calculated based on the prediction based on the pixel value of the target pixel and the pixel values of the surrounding pixels of the target pixel. Second prediction means for calculating a prediction error value for the pixel value of the target pixel of the prediction value obtained by the determination and prediction, and encoding of the prediction error value obtained by the first prediction means and the second prediction means Coding means for performing And features.

  The present invention is also an image processing method for compressing and encoding multi-value image data, and based on a correlation between at least one of a vertical direction and a horizontal direction of an image between a target pixel and peripheral pixels of the target pixel. A first prediction step for determining whether or not a prediction error value, which is a difference between a pixel value of a pixel and a prediction value with respect to a pixel value of a target pixel, is 0, and the prediction error value is 0 by the first prediction step. If it is determined that the pixel value of the target pixel is not, the prediction value for the pixel value of the target pixel is obtained by prediction based on the pixel value of the target pixel and the pixel values of the surrounding pixels of the target pixel. A second prediction step for calculating a prediction error value for each pixel value, and an encoding step for encoding the prediction error value obtained in the first prediction step and the second prediction step. To do.

  According to the present invention, it is possible to perform an image compression encoding process at a higher speed.

FIG. 1 is a schematic diagram illustrating a configuration example of a mechanism unit of an image forming apparatus to which an image processing apparatus according to an embodiment of the present invention can be applied. FIG. 2 is a block diagram showing a configuration of an example of the electrical / control apparatus in the image forming apparatus to which the image processing apparatus according to the embodiment of the present invention can be applied. FIG. 3 is a schematic diagram illustrating an example format of the main memory 210. FIG. 4 is a schematic diagram showing a format of an example of the CMYK band data storage area in the main memory. FIG. 5 is a flowchart of an example schematically showing image processing in a color printer to which the image processing apparatus according to the embodiment of the present invention can be applied. FIG. 6 is a block diagram showing a configuration of an example of an encoding unit according to the embodiment of the present invention. FIG. 7 is a schematic diagram for explaining the reading order of CMYK band data from the CMYK band data storage area. FIG. 8 is a schematic diagram for explaining pixels used in the prediction process. FIG. 9 is a flowchart illustrating an example of prediction processing by the LOCO-I method. FIG. 10 is a flowchart illustrating an example of prediction processing by the Paeth method. FIG. 11A is a schematic diagram illustrating an exemplary format of a code according to an embodiment of the present invention. FIG. 11B is a schematic diagram illustrating an exemplary format of a code according to an embodiment of the present invention. FIG. 12 is a schematic diagram illustrating a format of an example of a code according to the embodiment of the present invention. FIG. 13 is an example flowchart illustrating an encoding process according to an embodiment of the present invention. FIG. 14 is a flowchart showing an exemplary determination process in the simple prediction process according to the embodiment of the present invention. FIG. 15A is a schematic diagram illustrating an example of an actual printer image. FIG. 15B is a schematic diagram illustrating an example of an actual printer image. FIG. 16A is a schematic diagram used for verifying simple prediction processing according to the embodiment of the present invention. FIG. 16-2 is a schematic diagram used for verifying simple prediction processing according to the embodiment of the present invention. FIG. 17A is a schematic diagram used for verifying simple prediction processing according to the embodiment of the present invention. FIG. 17-2 is a schematic diagram used for verifying simple prediction processing according to the embodiment of the present invention.

  Exemplary embodiments of an image processing apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. FIG. 1 shows an example of the structure of a mechanism part of an image forming apparatus (referred to as a color printer) to which an image processing apparatus according to an embodiment of the present invention can be applied. In this embodiment, an example in which the image processing apparatus and the image processing method according to the present invention are applied to an image forming apparatus that is a color printer will be described. However, as long as image processing is performed on an image including a character image, However, the present invention is not limited to this. For example, the present invention can be applied to an image processing apparatus such as a copying machine, a facsimile machine, and a multifunction machine.

  A color printer 100 illustrated in FIG. 1 forms images of four colors (Y, M, C, K) by independent image forming systems 1Y, 1M, 1C, and 1K, and synthesizes these four color images. This is a 4-drum tandem engine type image forming apparatus. Each of the image forming systems 1Y, 1M, 1C, and 1K includes a photoconductor as an image carrier, for example, small-diameter OPC (organic photoconductor) drums 2Y, 2M, 2C, and 2K, and the OPC drums 2Y, 2M, and 2C. The electrostatic latent images on the charging rollers 3Y, 3M, 3C, and 3K as charging means and the OPC drums 2Y, 2M, 2C, and 2K are developed with a developer from the upstream side of image formation so as to surround 2K. Developing devices 4Y, 4M, 4C, and 4K that produce toner images of Y, M, C, and K colors, cleaning devices 5Y, 5M, 5C, and 5K, static eliminators 6Y, 6M, 6C, and 6K are disposed. .

  Beside each developing device 4Y, 4M, 4C, 4K, toner bottle units 7Y, 7M, 7C, 7K for supplying Y toner, M toner, C toner, K toner to the developing devices 4Y, 4M, 4C, 4K, respectively. Is arranged. In addition, each of the image forming systems 1Y, 1M, 1C, and 1K is provided with independent optical writing devices 8Y, 8M, 8C, and 8K. The optical writing devices 8Y, 8M, 8C, and 8K are laser diodes (laser light sources). LD) Light source 9Y, 9M, 9C, 9K, collimating lens 10Y, 10M, 10C, 10K, fθ lens 11Y, 11M, 11C, 11K, and other optical components, polygon mirrors 12Y, 12M, 12C, 12K as deflection scanning means And folding mirrors 13Y, 13M, 13C, 13K, 14Y, 14M, 14C, 14K, and the like.

  The image forming systems 1Y, 1M, 1C, and 1K are arranged vertically, and the transfer belt unit 15 is arranged on the right side so as to be in contact with the OPC drums 2Y, 2M, 2C, and 2K. The transfer belt unit 15 is rotationally driven by a drive source (not shown) with the transfer belt 16 stretched around rollers 17 to 20. A paper feed tray 21 storing transfer paper as a transfer material is disposed on the lower side of the apparatus, and a fixing device 22, a paper discharge roller 23, and a paper discharge tray 24 are disposed at the top of the apparatus.

  At the time of image formation, in each of the image forming systems 1Y, 1M, 1C, and 1K, the OPC drums 2Y, 2M, 2C, and 2K are rotationally driven by a driving source (not shown), and the OPC drums are charged by the charging rollers 3Y, 3M, 3C, and 3K. The 2Y, 2M, 2C, and 2K are uniformly charged, and the optical writing devices 8Y, 8M, 8C, and 8K perform optical writing on the OPC drums 2Y, 2M, 2C, and 2K based on the image data of each color, whereby the OPC drum Electrostatic latent images are formed on 2Y, 2M, 2C, and 2K.

  The electrostatic latent images on the OPC drums 2Y, 2M, 2C, and 2K are developed by developing devices 4Y, 4M, 4C, and 4K, respectively, to become toner images of colors Y, M, C, and K, while the paper feed tray 21 Then, the transfer paper is fed in the horizontal direction from the paper feed roller 25 and is conveyed vertically in the image forming systems 1Y, 1M, 1C and 1K by the transport system. This transfer paper is electrostatically held by the transfer belt 16 and conveyed by the transfer belt 16, and a transfer bias is applied by a transfer bias applying means (not shown), and Y on the OPC drums 2Y, 2M, 2C, 2K, A full color image is formed by sequentially superimposing and transferring toner images of M, C, and K colors. The transfer sheet on which the full-color image is formed is fixed to the full-color image by the fixing device 22 and is discharged to the discharge tray 24 by the discharge roller 23.

  The control of each part in the color printer 100 described above is performed by the electrical / control device 26.

  FIG. 2 is a block diagram showing a configuration of an example of the electrical / control apparatus 26 of FIG. In the example of FIG. 2, the electrical / control device 26 includes a CPU (Central Processing Unit) 200, a printer ASIC (Application Specific Integrated Circuit) 230, and a main memory 210. The printer ASIC 230 includes a CPU I / F 201, a main memory arbiter (ARB) 202, a main memory controller 203, an encoding unit 204, a decoding unit 205, a gradation processing unit 206, and an engine controller 207.

  The CPU 200 controls the overall operation of the color printer 100 according to a program stored in the main memory 210. The CPU 200 is connected to the main memory arbiter 202 via the CPU I / F 201. The main memory arbiter 202 arbitrates access to the main memory 210 by the CPU 200, the encoding unit 204, the decoding unit 205, and the communication controller 208.

  The main memory 210 is connected to the main memory arbiter 202 via the main memory controller 203. The main memory controller 203 controls access to the main memory 210. The main memory 210 stores the above-described program for operating the CPU 200 and drawing commands output from the CPU 200. The main memory 210 further stores various data such as band data and page compression data.

  The encoding unit 204 encodes band data stored in the main memory 210. The encoded band data is supplied to the main memory 210 via the main memory arbiter 202 and the main memory controller 203, and is written in the page code storage area. The decoding unit 205 reads out the encoded band data encoded by the encoding unit 204 and written in the main memory 210 from the main memory 210 in synchronization with a printer engine 211 described later. The decoded band data is supplied to the gradation processing unit 206. The gradation processing unit 206 performs gradation processing on the band data supplied from the decoding unit 205 and transfers the band data to the engine controller 207.

  The engine controller 207 controls the printer engine 211. In FIG. 2, only the C version of the printer engine 211 is shown, and the M, Y, and K versions are omitted to avoid complication.

  The communication controller 208 controls communication via the network 221. For example, PDL (Page Description Language) data output from the computer 220 is received by the communication controller 208 via the network 221. The communication controller 208 transfers the received PDL data to the main memory 210 via the main memory arbiter 202 and the main memory controller 203.

  The network 221 may be one that performs communication within a predetermined range such as a LAN (Local Area Network), or may be one that can communicate over a wider range than the Internet. The network 221 is not limited to wired communication but may be wireless communication, or may be serial communication such as USB (Universal Serial Bus) or IEEE (Institute Electrical and Electronics Engineers) 1394.

  FIG. 3 shows an exemplary format of the main memory 210. The program storage area 300 stores a program for the CPU 200 to operate. The PDL data storage area 301 stores, for example, PDL data supplied from the computer 220. The CMYK band data storage area 302 stores CMYK band data. The page code storage area 303 stores code data obtained by compression-coding band data. The page code storage area 303 can store code data for a plurality of pages. The area 304 stores data other than those described above.

  FIG. 4 shows an exemplary format of the CMYK band data storage area 302 in FIG. In this way, the CMYK band data storage area 302 has a plane configuration for each of the C, M, Y, and K plates, and 8 bits are assigned to each pixel. That is, the CMYK band data is a multi-value plane image in which each pixel has a bit depth of 8 bits.

  FIG. 5 is a flowchart of an example schematically illustrating image processing in the color printer 100 having the above-described configuration. The operation of the color printer 100 will be schematically described with reference to FIG. 2 described above using the flowchart of FIG.

  For example, PDL data generated by the computer 220 is received by the communication controller 208 via the network 221 and stored in the PDL data storage area 301 of the main memory 210 (step S1). The CPU 200 reads PDL data from the PDL data storage area 301 of the main memory 210, analyzes the PDL (step S2), and draws a CMYK band image based on the analysis result (step S3). The drawn CMYK band data based on the drawn CMYK band image is stored in the CMYK band data storage area 302 of the main memory 210 (step S4). As described above, this CMYK band data is multi-value plane image data in which each pixel has a bit depth of 8 bits.

  The encoding unit 204 reads CMYK band data from the CMYK band data storage area 302 and encodes it according to the predictive encoding method according to the embodiment of the present invention (step S5). Code data obtained by encoding the CMYK band data is stored in the page code storage area 303 of the main memory 210 (step S6).

  The decoding unit 205 reads and decodes code data obtained by encoding CMYK band data from the page code storage area 303, and supplies the decoded CMYK band data to the gradation processing unit 206 (step S7). The gradation processing unit 206 performs gradation processing on the CMYK band data supplied from the decoding unit 205 (step S8). The gradation-processed CMYK band data is supplied to the printer engine 211 via the printer engine controller 207 (step S9). The printer engine 211 performs printout based on the supplied CMYK band data.

<Outline of encoding process>
FIG. 6 shows an exemplary configuration of the encoding unit 204 according to the embodiment of the present invention. In the encoding unit 204, CMYK band data for each version of CMYK is read by the image reading unit 400 from the CMYK band data storage area 302 of the main memory 210. At this time, as illustrated in FIG. 7, CMYK band data for each plate of CMYK is sequentially read from the CMYK band data storage area 302 pixel by pixel by the image reading unit 400.

  The CMYK band data read in pixel units by the image reading unit 400 is stored in the line memory 402 by the line memory control processing unit 401. The line memory 402 is capable of storing CMYK band data for at least two lines. The line memory control process stores the data supplied this time and holds the data for one line stored immediately before. Controlled by the unit 401.

  For example, the line memory 402 has first and second areas each capable of storing pixels for one line, and when encoding of pixel data for one line is completed, pixels in the area where the encoding is completed Control is performed to hold the data and write the pixel data of the next line in the other region.

  Under the control of the line memory control processing unit 401, pixel data of a pixel to be encoded (hereinafter referred to as a target pixel) and pixel data of three pixels around the target pixel are read from the line memory 402, and simple prediction processing is performed. To the unit 410. Here, the peripheral three pixels read from the line memory 402 are pixels that have already been encoded and are close to the target pixel. More specifically, as illustrated in FIG. 8, the immediately preceding pixel a in the scan order of the target pixel and the previous line in the scan order with respect to the current line to which the target pixel belongs, that is, the target pixel The pixel b located immediately above the target pixel in the line immediately above the line to which it belongs and the pixel c immediately before in the scanning order of the pixel b.

  In the following, the line to which the target pixel to be encoded belongs is referred to as an encoding line, and the immediately preceding line in the scan order with respect to the encoding line is referred to as a reference line.

  The simple prediction processing unit 410 uses the pixel values of the pixel a, pixel b, and pixel c passed from the line memory control processing unit 401 and the pixel value of the target pixel to simplify the prediction value for the pixel value of the target pixel. (Hereinafter referred to as simple prediction processing). In this simple prediction processing, in the simple prediction processing unit 410, pixel values of two pixels adjacent to each other in the vertical direction or the horizontal direction for the four pixels a, b, and c and the pixel of interest are the vertical direction or It is determined whether or not there is a match in each row in the horizontal direction, that is, in each column in the vertical direction or each row in the horizontal direction.

  If it is determined that they do not match, the prediction processing unit 403 predicts the pixel value of the target pixel based on the pixel values of the pixels a, b, and c. In the present embodiment, the prediction processing unit 403 predicts the pixel value of the target pixel using the LOCO-I method or the Paeth method, which will be described later. These LOCO-I method or Paeth method are more compared to the planar prediction method for obtaining the inclination of the plane consisting of the pixels a, b, and c and the pixel of interest about the pixel a and the pixel b as axes. It is possible to obtain a predicted value with high accuracy.

  The prediction value obtained by the prediction processing unit 403 is supplied to the prediction error processing unit 404 together with the pixel value of the target pixel. The prediction error processing unit 404 calculates a difference between the pixel value of the target pixel and the prediction value obtained by the prediction processing unit 403 as a prediction error value. This prediction error value is supplied to the run length generation processing unit 405.

  On the other hand, the simple prediction processing unit 410 determines that the pixel values of two pixels adjacent in the vertical direction or the horizontal direction are the same in each column or each row for the four pixels a, b, and c and the target pixel. Then, the prediction error value is set to “0” and supplied to the run length generation processing unit 405. In this case, the processing by the prediction processing unit 403 and the prediction error processing unit 404 described above is not performed.

  When the target pixel is the first pixel in the line scan order and when the encoded line is the first line in the scan order, the prediction processing unit 403 and the prediction are assumed to have a predicted value of “0”. The error processing unit 404 is processed.

  The run length generation processing unit 405 increases the run length value by “1” when the prediction error value supplied from the simple prediction processing unit 410 or the prediction error processing unit 404 is “0”. When the prediction error value is directly supplied from the simple prediction processing unit 410 to the run length generation processing unit 405, the prediction error value is always “0”, so the run length value is “1” and increased. Is done. On the other hand, when the prediction error value is not “0”, the run length generation processing unit 405 passes the prediction error value, the run length value, and the pixel value of the target pixel to the code format generation processing unit 406, and then the run length. Reset the value.

  The code format generation processing unit 406 encodes the run length value and the prediction error value passed from the run length generation processing unit 405 according to a code format described later. As will be described in detail later, if the prediction error value is outside the range that can be expressed by the difference code, the pixel value itself of the target pixel is used as the code. The code generated by the code format generation processing unit 406 is transferred to the code writing unit 407 and written in the page code storage area 303 of the main memory 210.

<Example of prediction processing>
Here, the prediction method used in the prediction processing unit 403 will be described. As described above, in the present embodiment, LOCO-I (LOw COmplexity LOssless) capable of high-precision prediction is used for prediction processing for predicting the pixel value of the target pixel from the pixel values of the encoded pixels a, b, and c. COmpression for Images) method or Paeth method.

  In the following, as described with reference to FIG. 8, when encoding is performed from the left to the right of the image in pixel units and from the top to the bottom of the image in line units, it is adjacent to the left of the target pixel. In the following description, the pixel to be processed is pixel a, the pixel adjacent to the target pixel is pixel b, and the pixel in contact with the upper left of the target pixel is pixel c.

  First, the LOCO-I system will be described. In the LOCO-I method, the calculation method of the predicted value is switched according to the result of comparing the pixel value of the pixel c with the pixel values of the pixel a and the pixel b. FIG. 9 is a flowchart illustrating an example of prediction processing by the LOCO-I method. In the first step S30, it is determined whether or not the pixel value of the pixel c is greater than or equal to the pixel value of the pixel a and the pixel value of the pixel c is greater than or equal to the pixel value of the pixel b. If it is determined that the pixel value of the pixel c satisfies this condition, the process proceeds to step S31, the pixel value of the pixel a and the pixel value of the pixel b are compared, and the pixel having the smaller value is compared. The value is taken as the predicted value.

  On the other hand, in step S30, the pixel value of the pixel c does not satisfy the above condition, that is, the pixel value of the pixel c is less than the pixel value of the pixel a, or the pixel value of the pixel c is the pixel b. If it is determined that the value is less than the value, the process proceeds to step S32. In step S32, it is determined whether or not the pixel value of the pixel c is equal to or smaller than the pixel value of the pixel a and the pixel value of the pixel c is equal to or smaller than the pixel value of the pixel b. If it is determined that the pixel value of the pixel c satisfies this condition, the process proceeds to step S33, the pixel value of the pixel a and the pixel value of the pixel b are compared, and the pixel having the larger value is compared. The value is taken as the predicted value.

On the other hand, in step S32, the pixel value of the pixel c does not satisfy the above condition, that is, the pixel value of the pixel c is greater than or equal to the pixel value of the pixel a, or the pixel value of the pixel c is the pixel of the pixel b. If it is determined that the value is greater than or equal to the value, the process proceeds to step S34. In other words, this means that one of the pixel a and the pixel b has a pixel value greater than or equal to the pixel value of the pixel c, and the other pixel value is less than the pixel value of the pixel c. In step S34, the following equation (1) is calculated for the pixel values of the pixels a, b, and c, and the obtained value p is set as a predicted value.
p = a + b−c (1)

  Next, the Paeth method will be described. FIG. 10 is a flowchart illustrating an example of prediction processing by the Paeth method. In the Paeth method, a simple linear function of each pixel a, b, and c is calculated, and a value closest to the calculated value among the pixels a, b, and c is selected as a predicted value. More specifically, the value p is obtained by the above-described equation (1), and absolute differences pa, pb, and pc between the obtained value p and the pixel values of the pixels a, b, and c are calculated. A predicted value is selected from each of the pixels a, b, and c based on the calculated magnitude relationship between the difference absolute values pa, pb, and pc.

  In the first step S40, the value p is calculated from the pixel values of the pixels a, b and c according to the above equation (1). Then, in the next step S41, step S42 and step S43, absolute difference values pa, pb and pc between the value p and the pixel values of the respective pixels a, b and c are obtained.

  In FIG. 10, the operator abs indicates that the absolute value of the value in parentheses is obtained. In the following, in order to avoid complexity, the absolute difference values pa, pb, and pc are referred to as values pa, pb, and pc, respectively.

  When the values pa, pb, and pc are obtained by the process up to step S43, the process proceeds to step S44. In step S44, the value pa is compared with the value pb and the value pc, and it is determined whether or not the value pa is not more than the value pb and the value pa is not more than the value pc. If it is determined that the value pa satisfies this condition, the process proceeds to step S45, and the pixel value of the pixel a is set as a predicted value.

  On the other hand, in step S44, it is determined that the value pa is not more than the value pb and the value pa is not less than the value pc, that is, the value pa exceeds the value pb or the value pa exceeds the value pc. Then, the process proceeds to step S46. In step S46, the value pb is compared with the value pa and the value pc, and it is determined whether or not the value pb is equal to or less than the value pa and the value pb is equal to or less than the value pc. If it is determined that the value pb satisfies this condition, the process proceeds to step S47, and the pixel value of the pixel b is set as the predicted value.

  On the other hand, if it is determined in step S46 that the value pb is less than or equal to the value pa and the value pb is not less than or equal to the value pc, that is, the value pb exceeds the value pa or the value pb exceeds the value pc. The process proceeds to step S48, and the pixel value of the pixel c is set as a predicted value.

<Code format>
Next, an exemplary format of a code generated by the code format generation processing unit 406 will be described with reference to FIGS. 11A and 11B. In the present embodiment, the prediction error value and the run length value are each encoded. Then, as illustrated in FIG. 12, the encoded prediction error value (referred to as the encoded prediction error value) is connected after the encoded run length value (referred to as the encoded run length value), A code string is generated with a set of a coded run length value and a coded prediction error value as a unit.

  FIG. 11A illustrates a code format as an example of the encoded prediction error value. In the present embodiment, the prediction error value is Huffman encoded assuming that the larger the value, the lower the frequency. At this time, the prediction error values are grouped into ranges set in stages, and encoding is performed so that a different code length is assigned to each group. Group identification is performed using codes for the number of bits corresponding to the number of groups from the top of the generated Huffman code. In this embodiment, the prediction error values are classified into 8 groups, and 3 bits are used for group identification.

  Hereinafter, a bit used for group identification is referred to as a group identification bit, and a bit added to the group identification bit is referred to as an additional bit. The group identification bits and the additional bits constitute a unique Huffman code for each prediction error value.

In the present embodiment, a range is set for the prediction error value Pe as follows, for example, and the prediction error value Pe is classified into eight groups of group # 0 to group # 7.
Group # 0: Pe = 1, Pe = -1
Group # 1: Pe = -3, Pe = -2, Pe = 2, Pe = 3
Group # 2: −7 ≦ Pe ≦ −4, 4 ≦ Pe ≦ 7
Group # 3: −15 ≦ Pe ≦ −8, 8 ≦ Pe ≦ 15
Group # 4: −31 ≦ Pe ≦ −16, 16 ≦ Pe ≦ 31
Group # 5: −63 ≦ Pe ≦ −32, 32 ≦ Pe ≦ 63
Group # 6: −127 ≦ Pe ≦ −64, 64 ≦ Pe ≦ 127
Group # 7: Pe ≦ −128, 128 ≦ Pe

Further, the group identification bits and the bit lengths of the additional bits of each group are set as follows, for example.
Group # 0: Group identification bit = “000”, additional bit length = 1 bit Group # 1: Group identification bit = “001”, additional bit length = 2 bits Group # 2: Group identification bit = “010”, additional bits Length = 3 bit group # 3: Group identification bit = “011”, additional bit length = 4 bit group # 4: group identification bit = “100”, additional bit length = 5 bit group # 5: group identification bit = “101” ”, Additional bit length = 6 bits group # 6: group identification bit =“ 110 ”, additional bit length = 7 bits group # 7: group identification bit =“ 111 ”, additional bit length = 8 bits

  Here, when the prediction error value of the target pixel in group # 7 is smaller than −127 or larger than 127, the pixel value of the target pixel is used as it is as an additional bit without using the Huffman code. This is to prevent the code length from becoming larger than 8 bits and reducing the compression rate when the prediction error value is smaller than −255 or larger than 255.

  FIG. 11-2 illustrates a code format of an example of the encoded run length value. In the present embodiment, the run length value is Huffman coded so that the shorter the value, the shorter the code length is assigned, the run length value is “0”, the code length of 1 bit is assigned, and the code “0” is encoded. It becomes.

  Hereinafter, as illustrated in FIG. 11B, when the run length value is “1”, a 2-bit code length is assigned and encoded to a code “10”. When the run length values are “2” to “4”, a 4-bit code length is assigned and encoded into codes “1100”, “1101”, and “1110”, respectively.

  When the run length value is “5” or more, it is encoded into a format in which a numerical value part having a predetermined code length is connected after a code “1111” having a code length of 4 bits. As shown in the lower part of FIG. 11-2, the numerical value part is composed of one or a plurality of frames having a code length of 4 bits including a 1-bit header at the head, for example. The code indicating the run length value is divided every 3 bits, and the 3 bits excluding the header of each frame are packed so that the above-mentioned code “1111” side is the MSB. In the example of FIG. 11B, the maximum number of frames is limited to 7, and the run length value can be expressed up to “1048576”. When the run length value is “5”, the frame can be omitted.

  The header indicates whether or not the next frame follows a certain frame. For example, a header value “0” indicates that there is a next frame, and a header value “1” indicates that the frame ends.

<Details of predictive encoding processing>
Next, an example of predictive encoding processing performed by the encoding unit 204 according to the present embodiment will be described in more detail with reference to the flowchart of FIG. It is assumed that the run length value has been previously reset to 0 prior to the processing of the flowchart of FIG.

In step S <b> 10, the image reading unit 400 reads one pixel (target pixel G _DATA ) to be processed from the CMYK band data storage area 302 of the main memory 210. The read _target pixel G _DATA is written into an area of the line memory 402 where the pixel data of the encoded line is stored under the control of the line memory control processing unit 401 (step S11).

In the next step S23, the simple prediction processing unit 410 reads the pixel data of the three neighboring pixels a, b and c (see FIG. 8) of the pixel of interest G _DATA from the line memory 402 under the control of the line memory control processing unit 401. by using the pixel values of the pixels a, b and c, and the pixel value of the target pixel G _DATA, performing simple prediction process described above.

The determination in step S23 is made as follows. Regarding the pixels arranged in the vertical direction, the first condition is that the pixel value is the same between the pixel a and the pixel c, and the pixel value is the same between the pixel b and the target pixel _GDATA . Furthermore, for the pixels arranged in the horizontal direction, the pixel value at the pixel b and pixel c is equal and, a second condition that the pixel value is equal between the pixel of interest G _DATA pixel a. The simple prediction processing unit 410 determines whether or not at least one of the first condition and the second condition is satisfied.

By simple prediction in step S23, it is determined that the pixel values of two pixels adjacent in the vertical direction or the horizontal direction are the same in each column or each row for the four pixels a, b, and c and the target pixel G _DATA. In this case, the prediction error for the pixel value of the target pixel G _DATA is “0”. That is, in this case, it can be said that the pixel value of the target pixel G _DATA was predicted by a simple prediction process. In this case, the process proceeds to step S24, and the run length value is increased by “1”. Then, the process returns to step S10, the next pixel as a new target pixel G _DATA in scan order, the process is repeated.

On the other hand, in step S23, it is determined that the pixel values of two pixels adjacent in the vertical direction do not match at least one of the columns, and the pixel values of two pixels adjacent in the horizontal direction do not match at least one of the rows. If the result is YES, the process proceeds to step S12, and a prediction process is performed based on the pixel values of the pixels a, b, and c. In this case, the pixel value of the target pixel G _DATA cannot be predicted by a simple prediction process.

  FIG. 14 is a flowchart illustrating an exemplary determination process in the simple prediction process according to the present embodiment, which is performed in step S23. In this example, first, in step S50 and step S51, a match in the vertical direction (first condition) is determined, and then in step S52 and step S53, a match in the horizontal direction (second condition) is determined.

That is, it is determined in step S50 whether the pixel values of the pixel a and the pixel c are equal. If it is determined that the pixel values are equal in step S50, the process proceeds to step S51, and it is determined whether the pixel values of the pixel b and the target pixel G _DATA are equal. If it is determined in step S51 that they are equal, it is assumed that the pixel value of the target pixel _{GDATA has been} predicted by simple prediction, and the process proceeds to step S24.

On the other hand, if it is determined in step S50 that the pixel value is different between the pixel a and the pixel c, or if it is determined in step S51 that the pixel value is different between the pixel b and the target pixel _GDATA , the process is as follows. The process proceeds to step S52. In step S52, it is determined whether or not the pixel values of the pixel b and the pixel c are equal. If it is determined in step S52 that they are equal, the process proceeds to step S53, and it is determined whether or not the pixel values of the pixel a and the target pixel _GDATA are equal. If it is determined in step S53 that they are equal, it is determined that the pixel value of the target pixel _{GDATA has been} predicted by simple prediction, and the process proceeds to step S24.

On the other hand, when the pixel value at the pixel b and pixel c at step S52 described above it is determined to be different, or, if the pixel value is determined to differ between the pixel a and the pixel of interest G _DATA in step S53, simple In such prediction, it is assumed that the pixel value of the target pixel G _DATA cannot be predicted, and the process proceeds to step S12.

  Here, the first condition, i.e., processing for pixels arranged in the vertical direction is performed first, but this is not limited to this example, and the second condition, i.e., processing for pixels arranged in the horizontal direction may be performed first. Good.

In step S12, the prediction processing unit 403 predicts the pixel value of the target pixel G _DATA using the pixel values of the pixels a, b, and c. In the present embodiment, as described above, the prediction process is performed using the LOCCO-I method or the Paeth method capable of highly accurate prediction. In the next step S13, the prediction error processing unit 404, from the pixel value of the target pixel G _DATA, by subtracting the predicted prediction value in step S12, the error (prediction error value) of the predicted value for the target pixel G _DATA Ask for.

When the prediction error value for the target pixel G _DATA is obtained in step S13, the process proceeds to step S14. In step S14, the run length generation processing unit 405 determines whether the prediction error value obtained in step S13 is a value other than “0” or whether the target pixel G _DATA is the last pixel of the line. Is done.

If it is determined that the obtained prediction error value is “0” and the target pixel G _DATA is not the last pixel of the line, the process proceeds to step S15, and the run length value is set to “1”. increase. Then, the process is returned to step S10, and the process is repeated with the next pixel in the scan order as the new target pixel _GDATA .

On the other hand, if it is determined in step S14 that the predicted difference value is a value other than “0” or the target pixel _GDATA is the last pixel of the line, the process proceeds to step S16. In step S16, the run length value is encoded according to the encoding format described with reference to FIG. 11B to generate an encoded run length value. At this time, as described above, even if the run-length value is “0”, the run-length value is encoded, and a code “0” is generated with a 1-bit code length.

  In the next step S17 and step S18, the code format generation processing unit 406 encodes the prediction error value according to the encoding format described with reference to FIG. 11A to generate an encoded prediction error value. That is, in step S17, a group to which the prediction error value belongs is obtained based on the prediction error value, and a value indicating the group is encoded. In the next step S18, additional bits are encoded based on the prediction error value and the group obtained in step S17. Then, the encoded group and the additional bits are connected to generate an encoded prediction error value.

  The code writing unit 407 connects the encoded prediction error value obtained in step S18 to the encoded run length value obtained in step S16 and writes it in the page code storage area 303 of the main memory 210.

The process proceeds to step S19, and it is determined whether or not the _target pixel _GDATA is the last pixel of the line. If it is determined that the target pixel G _DATA is not the final pixel of the line, the process proceeds to step S20, and the run length value is reset to “0”. Then, the process is returned to step S10, and the process is repeated with the next pixel in the scan order as the new target pixel _GDATA .

On the other hand, if it is determined in step S19 that the target pixel _GDATA is the last pixel of the line, the process proceeds to step S21. In step S21, the line to which the _target pixel G _DATA belongs is held as it is in one area of the line memory 402 as an encoded reference line, and the other area of the line memory 402 is encoded next for encoding. The pixel data is stored in the area. Then, the process proceeds to step S22, and it is determined whether or not the process has been completed for all lines. If it is determined that the processing has been completed, a series of encoding processing is ended.

On the other hand, if it is determined in step S22 that the process has not been completed for all lines, the process returns to step S10, and the process is repeated with the first pixel of the next line as the target pixel _GDATA .

  Here, the validity of the simple prediction process in step S23 described above will be described. 15A and 15B show examples of actual printer images. FIG. 15A is an example in which characters and CG (Computer Graphics) images are arranged on a white background, which is frequently used in general business documents. Further, FIG. 15-2 is an example in which an image of characters or CG is arranged on the ground subjected to gradation processing in the vertical direction of the image, and such a format is also a general business document or the like. Often used.

In such a printer image composed mainly of CG and text, pixels are arranged with a certain regularity, and it is expected to have a high correlation in pixel units in the horizontal and vertical directions of the image. Here, when the correlation in the horizontal direction is high, referring to FIG. 8 described above, the pixel values of the pixel b and the pixel c are equal, and the pixel value of the pixel a and the target pixel G _DATA are equal. It is. The case where the correlation in the vertical direction is high is a case where the pixel value is the same between the pixel a and the pixel c, and the pixel value is the same between the pixel b and the target pixel _GDATA . Therefore, in the case of an image having a high correlation in the horizontal direction and the vertical direction as described above, whether or not the pixel values of the two pixels adjacent in the vertical direction or the horizontal direction match in each column or each row as described above. hits are predicted by simple prediction process for determining the prediction error for the pixel value of the target pixel G _DATA is "0".

A simple prediction process according to the present embodiment will be verified with reference to FIGS. 16 and 17. FIGS. 16A and 16B perform prediction using the LOCO-I method and verify simple prediction processing. FIG. 16A illustrates an example of an image having a high correlation in the horizontal direction. In the example of FIG. 16A, the pixel values of the pixel b and the pixel c arranged in the horizontal direction are each “100”, and the pixel value of the pixel a and the target pixel G _DATA are each “20”. According to the simple prediction process of the present embodiment, the pixel value is the same for the pixel b and the pixel c, and the pixel value is the same for the pixel a and the target pixel G _DATA , so according to the determination described in step S23. The prediction error for the pixel value of the target pixel G _DATA is “0”.

  In the case of this example, referring to the flowchart of FIG. 9 described above, the pixel value is the same for the pixel c and the pixel b, and the pixel value of the pixel c is larger between the pixel c and the pixel a. The process proceeds to step S31. Since the pixel a has a smaller pixel value between the pixel a and the pixel b, the predicted value is “20”, which is the pixel value of the pixel a. Since the pixel value of the target pixel is “20”, the prediction is correct, and the prediction error is “0”. This coincides with the result of the simple prediction process according to the present embodiment. In the figure, the operator min indicates that the smaller one of the values written in parentheses is selected.

FIG. 16B illustrates an example of an image having a high correlation in the vertical direction. In the example of FIG. 16B, the pixel values of the pixels a and c arranged in the vertical direction are “80”, and the pixel values of the pixel b and the target pixel G _DATA are “30”. According to the simple prediction process of the present embodiment, the pixel value is the same between the pixel a and the pixel c, and the pixel value is the same between the pixel b and the target pixel G _DATA , so according to the determination described in step S23. The prediction error for the pixel value of the target pixel G _DATA is “0”.

  In the case of this example, referring to the flowchart of FIG. 9 described above, the pixel value is the same for the pixel a and the pixel c, and the pixel c is larger in the pixel c and the pixel b. The process proceeds to step S31. Since the pixel value of the pixel b is smaller between the pixel a and the pixel b, the predicted value is set to “30” which is the pixel value of the pixel b. Since the pixel value of the target pixel is “30”, the prediction is correct, and the prediction error is “0”. This coincides with the result of the simple prediction process according to the present embodiment.

  FIGS. 17A and 17B are examples in which prediction is performed using the Paeth method. The pixel values of the pixels a, b, and c and the pixel of interest are the same as those in FIGS. 16-1 and 16-2 described above, respectively. Therefore, the prediction errors due to the simple prediction processing according to the present embodiment are “0” in FIGS. 17A and 17B, respectively, as described above.

In the case of the example in FIG. 17A, referring to the flowchart in FIG. 10, the pixel value of the pixel a is “20”, and the pixel values of the pixel c and pixel b are “100”. When the value p is calculated from the pixel values of a, b and c, the value p = 20 + 100−100 = 20. When the values pa, pb, and pc are obtained in steps S41 to S43 using this value p, the values pa = 0, pb = 80, and pc = 80 are obtained. Since the value pa is equal to or less than the value pb and the value pc, the value a = 20 is set as the predicted value by the determination in step S44. Since the pixel value of the target pixel G _DATA is “20”, the prediction error is “0”, which matches the result of the simple prediction process according to the present embodiment.

In the case of the example of FIG. 17-2, referring to the flowchart of FIG. 10, the pixel values of the pixel a and the pixel c are “80” and the pixel value of the pixel b is “30”. When the value p is calculated from the pixel values of a, b and c, the value p = 80 + 30−80 = 30. When the values pa, pb, and pc are obtained in steps S41 to S43 using this value p, the values pa = 50, the value pb = 0, and the value pc = 50 are obtained. Since the value pa is larger than the value pb, the process proceeds to step S46 according to the determination in step S44. Since the value pb is smaller than the value pa and the value pc, the value b = 30 is set as the predicted value by the determination in step S46. Since the pixel value of the pixel of interest G _DATA is “30”, the prediction error is “0”, which matches the result of the simple prediction process according to the present embodiment.

  As described above, according to the simple prediction process of the present embodiment, the same result as the prediction by the LOCO-I method or the Paeth method is obtained in the portion where there is a correlation in the vertical direction or the horizontal direction in the image. Compared to the method and the Paeth method, it can be obtained with much fewer procedures. Therefore, according to the present embodiment, predictive coding of an image can be performed at a higher speed while maintaining high-precision prediction by the LOCO-I method or the Paeth method.

  In this embodiment, the code format is configured to indicate that the prediction error value is “0” by a run length value having a code length of 1 bit, and the code is a unit of a set of the run length value and the prediction error value. It is configured as. Therefore, the encoding process and the decoding process can be simplified. Also, by configuring the code in this way, it is not necessary to include a header indicating the run-length value and the prediction error value, or a header indicating the prediction process used at the time of encoding, and compression encoding can be performed more efficiently. It can be performed.

<Other embodiments>
In the above description, each unit configuring the encoding unit 204 according to the embodiment of the present invention has been described as being configured in hardware, but this is not limited to this example. That is, the encoding unit 204 in the color printer 100 applicable to the embodiment of the present invention can be realized as a program that operates on a CPU (not shown) incorporated in the color printer 100.

  In this case, the program executed as the encoding unit 204 on the CPU is, for example, each functional unit (the image reading unit 400, the line memory control processing unit 401, the simple prediction processing unit) of the encoding unit 204 described with reference to FIG. 410, a prediction processing unit 403, a prediction error processing unit 404, a run length generation processing unit 405, a code format generation processing unit 406, and a code writing unit 407).

  This program is a file in an installable or executable format, and is provided by being recorded on a computer-readable recording medium such as a CD (Compact Disk), a flexible disk (FD), or a DVD (Digital Versatile Disk). . The program is not limited to this, and the program may be stored in advance in a ROM (not shown) connected to the CPU. Furthermore, the program may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. The program may be configured to be provided or distributed via a network such as the Internet.

  As actual hardware, for example, the CPU reads out and executes a program that functions as the encoding unit 204 from the above-described recording medium, whereby each of the above-described units is loaded on a main storage device (not shown). Then, an image reading unit 400, a line memory control processing unit 401, a simple prediction processing unit 410, a prediction processing unit 403, a prediction error processing unit 404, a run length generation processing unit 405, a code format generation processing unit 406, and a code writing unit 407 are provided. It is generated on the main memory.

204 Coding unit 205 Decoding unit 210 Main memory 302 CMYK band data storage area 303 Page code storage area 401 Line memory control unit 402 Line memory 403 Prediction processing unit 404 Prediction error processing unit 405 Run length generation processing unit 406 Code format generation processing unit 410 Simple prediction processing unit

JP 2002-344323 A Japanese Patent No. 2888186 JP-A-11-234683

Claims (10)

An image processing apparatus for compressing and encoding multi-value image data,
Prediction that is the difference between the pixel value of the pixel of interest and the predicted value for the pixel value of the pixel of interest based on the correlation of at least one of the vertical and horizontal directions of the image between the pixel of interest and the surrounding pixels of the pixel of interest First prediction means for determining whether or not the error value is 0;
When it is determined by the first prediction means that the prediction error value is not 0, the prediction value for the pixel value of the pixel of interest is determined as the pixel value of the pixel of interest and the pixel values of the surrounding pixels of the pixel of interest. Second prediction means for calculating a prediction error value for the pixel value of the target pixel of the target pixel of the prediction value determined by the prediction,
An image processing apparatus comprising: an encoding unit that encodes the prediction error value obtained by the first prediction unit and the second prediction unit. The first prediction means includes
Determining that the prediction error value is 0 when the pixel of interest and the peripheral pixels of the pixel of interest have the same pixel value in each of at least one of the vertical direction and the horizontal direction. The image processing apparatus according to claim 1, wherein: The image processing apparatus according to claim 1, wherein the second prediction unit obtains the predicted value using a LOCO-I method. The image processing apparatus according to claim 1, wherein the second prediction unit obtains the predicted value using a Paeth method. A run length generating means for generating a run length in which the prediction error value obtained by the first predicting means and the second predicting means has a length of 0;
The encoding means includes
2. The encoding method according to claim 1, wherein the prediction error value obtained by the first prediction unit and the second prediction unit and the run length generated by the run length generation unit are encoded. Item 5. The image processing apparatus according to any one of Items 4 to 5. The encoding means includes
The image processing apparatus according to claim 5, wherein the run length and the prediction error value are encoded using a Huffman code. The encoding means includes
The image processing apparatus according to claim 6, wherein the run length and the prediction error value are encoded based on mutually independent Huffman trees. The encoding means includes
When the code length of the Huffman code corresponding to the prediction error value is equal to or longer than the bit length of the image data of the target pixel, the image data itself of the target pixel is used as the encoded code. The image processing apparatus according to claim 6 or 7, wherein the image processing apparatus is characterized in that: The encoding means includes
The code data is formed in units of a set of the run length that has been encoded and the prediction error value that has been encoded, according to any one of claims 5 to 8. The image processing apparatus described. An image processing method for compressing and encoding multi-value image data,
Prediction that is the difference between the pixel value of the pixel of interest and the predicted value for the pixel value of the pixel of interest based on the correlation of at least one of the vertical and horizontal directions of the image between the pixel of interest and the surrounding pixels of the pixel of interest A first prediction step for determining whether the error value is 0;
When it is determined in the first prediction step that the prediction error value is not 0, a prediction value for the pixel value of the target pixel is determined as a pixel value of the target pixel and a pixel value of a peripheral pixel of the target pixel. A second prediction step of calculating a prediction error value for the pixel value of the target pixel of the target pixel of the prediction value obtained by the prediction,
An image processing method comprising: an encoding step for encoding the prediction error value obtained in the first prediction step and the second prediction step.