JP2009076992A - Image coding device and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain coded data of high compression efficiency by not only suppressing the variation of a coding parameter but also increasing a probability that the coding parameter becomes a value suitable for run. <P>SOLUTION: When run-length coding an elementary pixel Xi, the run of a pixel one line preceding the elementary pixel Xi is acquired from an array variable, and the coding parameters J, K of the run including the elementary pixel is determined (step S903). Then, the run RL from the elementary pixel is counted (S905-S908). Then, the acquired coding parameter is defined as an initial parameter when coding the run RL including the elementary pixel, and the run including the elementary pixel is run-length coded while updating the coding parameter (step S911). Then, the array variable is updated by the run including the elementary pixel (step S912). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image data encoding technique.

  Conventionally, a run-length encoding method that encodes the number of consecutive pixels having the same value is widely known.

  For example, as a method using the run-length encoding, JPEG-LS (Non-patent Document 1), which is an international standard method, is known.

  FIG. 1 is a flowchart showing the flow of processing in the run-length encoding mode in JPEG-LS.

  The flow of run length encoding processing in JPEG-LS will be described below with reference to FIG. The scan order of pixels at the time of encoding is the raster scan order.

  Before entering the run-length encoding mode, it is assumed that the run length n and the flag f indicating whether or not the run to be encoded is on the end of the image are determined. FIG. 2 shows the relationship between the run index value J and the value K changed by the run index. If the initial value of the run index J is “0”, the value of K is “0”. When the flag f is “1”, it indicates that the target run has reached the right end of the image. When the flag f is “0”, it indicates that the end position of the target run has not reached the right end of the image. Show.

When encoding a run of length n, first, in step 101, n is compared with 2 ^k (step S101). If n> 2 ^k (YES), the routine proceeds to step 102 where “1” (1 bit) is output. In step S, the result obtained by subtracting 2K from n is set as a new n. That is, n is updated. Thereafter, in step S104, 1 is added to the run index J to update the run index J, and the process returns to step S101.

On the other hand, if it is determined in step S101 that n ≦ 2 ^k , the process proceeds to step S105. In step S105, a flag f indicating whether or not the run of interest is on the edge of the image is checked. If it is determined that the flag f is “0”, “0” (1 bit) is output in step S106. In step S107, the remaining length of the run is encoded using K bits and output. In step S108, 1 is updated from the run index J.

  If it is determined in step S105 that the flag f is other than “0” (flag f is “1”), the process proceeds to step S109, where n is compared with “0”. If it is determined that n> 0, “1” is output, and if n = 0, the process ends without doing anything.

When the next run is encoded, the run index is dynamically changed by using the updated run index value as the initial value, and a value suitable for the run length is gradually obtained. Will be assigned.
ITU-T TT. 87 | ISO / IEC14495-1

  As described above, there is a run-length encoding mode as one of JPEG-LS encoding modes. In this run-length coding, a coding parameter such as a run index is dynamically changed so that an optimum code is assigned to the run length. In the case of this method, if runs of the same length are continuous, an optimum code is gradually assigned, and the amount of codes can be minimized. However, in the case of an image in which short runs and long runs are generated alternately, the run index may not converge to an appropriate value, and many codes may be generated.

  The present invention has been made in view of the above problems, and not only suppresses fluctuations in coding parameters, but also increases the probability that the coding parameters become values suitable for a run, thereby encoding at a high compression rate. The present invention intends to provide an encoding technique for generating data.

In order to solve this problem, for example, an image encoding device of the present invention has the following configuration. That is,
An image encoding device that inputs pixel data in raster scan order and performs run-length encoding according to dynamically updated encoding parameters,
Storage means for storing, for each pixel position, encoding history information for specifying the encoding parameter updated by performing run-length encoding;
An acquisition unit that acquires, from the storage unit, encoding history information of a pixel position of the previous line that is the same as the horizontal position of the target pixel when run-length encoding a run from the position of the target pixel; ,
The encoding parameter specified by the encoding history information acquired by the acquisition unit is set as an initial encoding parameter of the encoding of the run, and the initial encoding parameter is updated according to the run, and the run Encoding means for run-length encoding
Storage means for storing, in the storage means, information for specifying the encoding parameter after encoding the run by the encoding means as encoding history information of each pixel constituting the run.

  According to the present invention, it is possible not only to suppress fluctuations in coding parameters, but also to increase the probability that the coding parameters will be a value suitable for a run, and to obtain coded data with a high compression rate.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment]
FIG. 8 is a diagram showing a basic configuration of an image encoding device according to this embodiment.

  A CPU 1401 functions as a control unit that controls the entire apparatus. A RAM 1402 stores a program executed by the CPU 1401 and is used as a work area. A ROM 1403 stores a BIOS and a boot program. Reference numeral 1404 denotes a keyboard, and 1405 denotes a mouse which is a pointing device. Reference numeral 1406 denotes a display device, which includes a display device such as a CRT or LCD. Reference numeral 1407 denotes a large-capacity external storage device typified by a hard disk device or the like, in which an OS and a program for encoding / decoding processing according to the embodiment are stored. The external storage device 1407 is also used for storing various data files. A storage medium drive 1408 reads programs and data recorded on a storage medium such as a CD-ROM or DVD-ROM and outputs them to the RAM 1402 or the external storage device 1407. Note that a program for image encoding processing (to be described later) and encoding target image data may be recorded as files on this storage medium. In this case, the storage medium drive 1408 loads the program and data into a predetermined area on the RAM 1402 under the control of the CPU 1401.

  Reference numeral 1409 denotes an I / F, which connects an external device to the present apparatus through the I / F 1409 and enables data communication between the present apparatus and the external apparatus. For example, image data to be encoded is input to the RAM 1402 or the external storage device 1407 of the apparatus via the I / F 1409, or conversely, an image generated from the RAM 1402 or the external storage apparatus 1407 of the apparatus. The encoded data can be output outside the apparatus. A bus 1410 connects the above-described units.

  In the above configuration, when the power of this apparatus is turned on, the CPU 1401 loads the OS from the external storage device 1407 to the RAM 1402 and executes it in accordance with the boot program stored in the ROM 1403. As a result, this apparatus functions as an information processing apparatus. Further, when the user operates the mouse 1405 to give an instruction to start image encoding / decoding, the CPU 1401 loads the corresponding application program from the external storage device 1407 to the RAM 1402 and executes it. As a result, this apparatus functions as an image encoding apparatus or an image decoding apparatus.

  The following is a description of a case where an image encoding application is executed and this apparatus functions as an image encoding apparatus that performs lossless encoding of image data.

  In order to simplify the description, it is assumed that the size of the image data to be encoded is W pixels in the horizontal direction and H pixels in the vertical direction. A pixel is represented by three luminance components of R, G, and B, each of which has 8 bits (256 gradations). Further, it is assumed that the order of inputting the image data to be encoded is dot-sequential, that is, raster scan order, and the data constituting each pixel is arranged in the order of R, G, and B. The type of color space is not limited to RGB, and may be YMCK, or may be the type of color space, and the number of components is not limited. If it is a monochrome image, it becomes one component (density or luminance).

  The generation source of image data to be encoded may be the result of rendering processing of data such as an external storage device 1407 (image data file), an image scanner connected to the interface 1409, or print data. It doesn't matter. The encoded data is stored (output) as a compressed file in the external storage device 1407, but the type of output target is not limited.

  In this embodiment, prior to starting the encoding process, an array variable D (x, C) corresponding to one line of an image, that is, the number W of pixels in the horizontal direction, is set in advance in the RAM 1402. Secure in the storage area. Here, an example in which the array variable D (,) is secured in the RAM 1402 is shown, but the type thereof is not limited as long as it is in a rewritable memory such as a hard disk.

  Here, the variable x specifies the pixel position in the horizontal direction, and the range that the variable x can take is 0 ≦ x ≦ W−1. That is, this array variable can be said to be a variable that holds information for each pixel position indicated by the coordinate x. The argument C is a value of 0 or 1. In D (x, 0), identification information for identifying the type of encoding is stored. There are two types of encoding in the embodiment: run-length encoding using parameters J and K and predictive encoding. In D (x, 1), the run (number of continuous pixels) when run-length encoding is stored.

  For example, when D (x, 0) is “0”, it indicates that the pixel at the coordinate x in the horizontal direction is run-length encoded. The value indicated by D (x, 1) indicates the run. Further, when D (x, 0) is “1”, it indicates that the pixel at the coordinate x in the horizontal direction has been predictively encoded.

  In the following description, a pixel of interest at coordinates (x, y) to be encoded is expressed as Xi. The array variable D (,) is used to determine the coding history of the pixel at the coordinate (x, y−1) one line before the pixel of interest Xi. That is, the encoding type of the coordinate (x, y−1) one line before the pixel of interest Xi is determined according to D (x, 0). Further, when the encoding type of the coordinate (x, y−1) one line before the pixel of interest Xi is run-length encoded, the value of D (x, 1) is checked to determine the run. Judge how many.

  In this embodiment, when the target pixel Xi is a pixel to be run-length encoded, parameters J and K for encoding a run including the target pixel Xi are determined from the encoding history of the pixel one line before. And is to be encoded.

  Hereinafter, the encoding processing procedure in the embodiment will be described with reference to the flowchart of FIG. Prior to starting encoding, the external storage device 1407 stores the header of the output file. This header stores data necessary for decoding, such as the number of pixels (size information) in the horizontal and vertical directions of the image data, the type of color space, and the number of bits of the color component. The encoded data generated in the following description is stored as data following this header.

  First, in step S301, the array variable D (,) is secured in the RAM 1402, and the value of the array variable is initialized. In the initialization process, D (, 0) = 0 and D (, 1) = 0. That is, all are run-length encoded and the run is set to “0”. However, the initial value may be the same as that of the decoding device, and the present invention is not limited to the initial value.

  Next, in step S302, the variable y indicating the vertical coordinate is initialized with “0”, and in step S303, the variable x indicating the horizontal coordinate is initialized with “0”.

  Thereafter, the process proceeds to step S304, and it is determined whether the four neighboring pixels Xa, Xb, Xc, and Xd located in the vicinity of the pixel of interest Xi indicated by the coordinates (x, y) have the same color. In other words, in step S304, it can be said that it is determined whether or not the number of colors of the neighboring pixels {Xa, Xb, Xc, Xd} is “1”.

  The relative positional relationship between the pixel of interest Xi and the neighboring pixels Xa, Xb, Xc, and Xd is as shown in FIG. That is, the neighboring pixels Xa, Xb, Xc, and Xd are signed pixels in the vicinity of the target pixel. When the target pixel Xi is at the boundary position of the image, all or some of the neighboring pixels Xa, Xb, Xc, and Xd are located outside the image. In this way, the neighboring pixels located outside the image are considered to have components R, G, and B of “0”. However, since this value may be shared by the decoding device, this does not limit the present invention.

  When the four neighboring pixels are equal to each other (when the number of colors is “1”), the probability that the pixel of interest Xi is equal to the neighboring pixel Xa is very high. Therefore, the process proceeds to step S305, and a run-length encoding process is performed (details will be described later). Thereafter, the process proceeds to step S309.

  On the other hand, if it is determined in step S304 that the number of colors represented by the four neighboring pixels is 2 or more, the process proceeds to step S306, where each color component constituting the pixel of interest Xi is predictively encoded, and the encoded data Is output. In the present embodiment, this predictive encoding process is assumed to follow the procedure defined in JPEG-LS. An example is as follows.

  Hereinafter, a case where the color component R of the pixel of interest Xi is encoded will be described. For the G component, the encoding target is simply changed from the R component to the G component. The same applies to the B component.

The R component of the pixel of interest Xi and the R components of neighboring pixels Xa, Xb, and Xc are expressed as Xi (R), Xa (R), Xb (R), and Xc (R). First, the predicted value P of the R component of the pixel of interest is obtained. In JPEG-LS, several formulas are defined in order to obtain the predicted value P. Here, for the sake of simplicity, the predicted value P is also obtained as follows.
P = Xa (R) + Xb (R) -Xc (R)

Next, the prediction error e between Xi (R), which is the R component of the pixel of interest, and the predicted value P is calculated.
e = Xi (R) -P

  Thereafter, the prediction error e is entropy-encoded (for example, Huffman encoding, Golomb encoding, arithmetic encoding, etc.), and the code word (encoded data) is output.

  When the encoded data of the R component of the pixel of interest Xi is generated and output as described above, the G component and the B component of the pixel of interest Xi are processed in the same manner, thereby encoding all the color components of the pixel of interest Xi. The process is performed.

  Thereafter, in order to indicate that the target pixel Xi has been subjected to predictive encoding, “1” is stored in the array variable D (x, 0) specified by the x coordinate of the target pixel in step S307.

  In addition, since predictive encoding is performed in units of one pixel, in step S308, the variable x is increased by “1”, and the process proceeds to step S309.

  In step S309, the variable x and the variable W are compared. If it is determined that x <W, the position of the pixel of interest Xi has not reached the right end position, and the process returns to step S304.

  If it is determined in step S309 that x = W, the process proceeds to step S310, the variable y is increased by “1”, and the process proceeds to step S311.

  In step S311, the variable y is compared with the variable H. If it is determined that y <H, the pixel of interest is not on the final line, so the processing from step S303 is performed. Also. If it is determined that y = H, the encoding is completed for all the pixels of the image data, and thus this processing ends.

  Next, details of the run-length encoding process in step S305 will be described with reference to the flowchart of FIG. In the following description, it should be noted that the coordinates of the target pixel Xi are specified by the variables x and y used in the processing of FIG.

  First, in step S901, a variable RL for counting runs and a flag f are each initialized with “0”.

  Next, the process proceeds to step S902, where the variable D (x, 0) is examined to predict whether the pixel one line before the pixel of interest Xi, that is, the pixel at coordinates (x, y-1) has been run-length encoded. It is determined whether it is error encoded.

  If it is determined that the pixel one line before the target pixel Xi is run-length encoded, the process proceeds to step S903. In step S903, the run of the pixel one line before the target pixel Xi is acquired by reading the variable D (x, 1). Then, initial parameters J and K for performing run-length encoding of the pixel of interest are determined according to the value of D (x, 1). The method for obtaining these parameters J and K is as follows.

  In order to simplify the description, it is assumed that the pixel of interest Xi is at the “*” position in FIG. FIG. 5 shows an example in which a black vertical line exists on a white background. Note that the left side of the target pixel Xi on the line where the target pixel Xi exists and the line above the target pixel Xi are encoded regions.

  In this encoded area, a pixel whose encoding type is predictive encoding (D (, 0) = 1) is “R”, and if run-length encoding (D (, 0) = 0), When expressed by a numerical value (D (, 1)) indicating a run, the image of FIG. 5 can be expressed as shown in FIG. In FIG. 6, a pixel “−” indicates that D (,) has been overwritten by the encoding process of the pixel on the left side of the target pixel Xi on the target line.

FIG. 6 shows that the type of encoding of the pixel (coordinate (x, y−1)) one line before the pixel of interest Xi is run-length encoding, and the run is “4”. In the present embodiment, an index q when the run “4” is expressed by 2 ^q + m is obtained. Since the numerical value “4” is 2 ² +0, the index q is “2”. Actually, such a complicated operation is unnecessary. That is, when the run is expressed in binary, the bit position that first appears at “1” from the MSB to the LSB may be obtained as q. Then, the obtained q is determined as a parameter K.

  The parameter J is obtained as follows.

  First, the table of FIG. 2 is examined from the left to the right, and the run index value at the position where the same value as the determined parameter K is first found is determined as the parameter J. In the case of FIG. 2, K = 2 is first determined because the run index value is “8”, and the parameter J is determined as “8”.

  The above is the procedure for determining the parameters J and K in step S903.

  On the other hand, in step S902, when the pixel one line before the pixel of interest Xi, that is, the pixel at the coordinate (x, y−1) is predictively encoded (when D (x, 0) = 1). Advances to step S904. In step 904, the default values are set in the parameters K and J without considering the array variable D (,). The default value may be the same value as the decoding device. In this embodiment, the parameters K and J are determined to be “0”.

  When the parameters J and K are obtained as described above, the process proceeds to step S905, and run detection and encoding processing are performed.

  First, in step S905, it is determined whether the pixel of interest Xi and the immediately preceding pixel Xa have the same color (here, the coordinates of the pixel Xa are (x-1, y)). Two pixels have the same color when the values of the two components are equal to each other.

  If it is determined that the target pixel Xi and the pixel Xa are equal, the process proceeds to step S906, and the variable RL is increased by “1”. In order to update the position of the pixel of interest Xi, the variable x is increased by “1” in step S907. Thereafter, the process proceeds to step S908, and the variable x and the variable W are compared. If x <W, it indicates that the pixel of interest has not reached the right edge of the image, and the process returns to step S905. On the other hand, if it is determined that the variable x and the variable W are equal, it indicates that the pixel of interest is located at the right end of the image, so “1” is set in the flag f, and the process proceeds to step S910.

  The loop from step S905 to step S908 is nothing but finding the number of consecutive pixels of the same color, that is, a run.

  If it is determined in step S905 that the pixel of interest Xi and the immediately preceding pixel Xa are different colors, or in step S908, the pixel of interest reaches the right end position of the image while the same color continues. If it is determined that the process has been performed, the process proceeds to step S910.

  Thereafter, in step S910, the value of variable RL is substituted for variable n, and in step S911, run-length encoding of variable n is performed. The contents of the run-length encoding process in step S911 are as shown in the flowchart of FIG. In FIG. 1, a run to be encoded is represented by a variable n. For this reason, in step S910, the value of the variable RL is stored in the variable n for convenience.

In step S912, processing for updating RL array variables D (,) from the first pixel position of the run is performed in preparation for the encoding processing of the line next to the line where the pixel of interest Xi exists. If the x coordinate of the head of the encoded run is represented by xs,
Each of D (xs, 0), D (xs + 1, 0),..., D (xs + RL-1, 0) is stored as “0”. In other words, history information indicating that the RL range of pixel groups from the pixel position of the coordinate xs in the horizontal direction has been run-length encoded is stored in the array variable D (,) and updated. Similarly, D (Xs, 1), D (Xs + 1,1),..., D (Xs + RL-1, 1) stores the value of the variable RL (run including the target pixel).

  In the flowchart of FIG. 3, “Yes” is determined in step S304, and it is determined in first step S905 that the processing according to the flowchart of FIG. 9 is started, the target Xi is not equal to the immediately preceding pixel Xa. Can also happen. In this case, the run “0” is encoded and output. In the case of run “0”, the pixel of interest Xi is not subject to encoding in the process of FIG. 9, but is predictively encoded in the process of FIG.

  As described above, according to the present embodiment, the initial parameters J and K for encoding a run including the target pixel Xi are determined according to the encoding history of the pixels on the line immediately before the target pixel Xi. As a result, it is possible to suppress the fluctuation of the parameters, increase the probability of maintaining the optimum parameters for the run, and improve the compression efficiency.

  In the embodiment, the first line at the start of image encoding is described as being encoded using the array variable D (,) initialized with the initial value. However, this does not limit the present invention. That is, for the first line of the image, the same processing as in the past may be performed to update the parameters J and K. However, in this case as well, if the array variable D (,) corresponding to the pixel position that has already been encoded is the information indicating the encoding type used at that time, and if run-length encoding is performed, that run is indicated. It will be updated with the coding history information of the information.

  In the above embodiment, when encoding a run including the target pixel Xi, if the encoding type of the pixel one line before the target pixel Xi is prediction error encoding, the default value is used. This has been described (step S904 in FIG. 9). However, instead of using this default value, the parameter J updated in the encoding process of the immediately preceding run may be used.

  Furthermore, in the embodiment, an example in which run-length encoding and prediction error encoding are used has been described. However, only run-length encoding may be used. In this case, since there is only one type of encoding, the array variable D only needs to store a run.

  In the embodiment, the condition for starting run-length encoding is that the four pixels Xa, Xb, Xc, and Xd in the vicinity of the target pixel Xi are equal to each other, that is, the number of colors indicated by the four neighboring pixels is “1”. An example has been described. However, the user may be able to select one threshold value from among candidates whose values are sufficiently smaller than the maximum number of colors represented by neighboring pixels, for example, {1, 2}. In this case, run-length encoding is performed when the number of colors of neighboring pixels is equal to or less than the threshold, and predictive encoding is performed when the threshold is exceeded. However, since the threshold value is selected by the user, it is necessary to store information for specifying the threshold value in the header of the encoded data file to be generated.

  In addition, when decoding the encoded image data generated by the image encoding device of the above-described embodiment, a process reverse to the above may be performed. When the target pixel is the first pixel of the image data to be encoded (the pixel at the upper left corner of the image), the target pixel is run-length encoded. This is because it is determined that the neighboring pixels Xa, Xb, Xc, and Xd outside the image are all the same color. However, except for the first pixel, predictive encoded data is basically positioned before one run-length encoded data. Therefore, if the pixel data obtained by decoding the predicted encoded data is Xp, pixel data Xp corresponding to the number indicated by the run obtained by decoding the run-length encoded data may be output.

  In the above embodiment, the argument of the array variable D (,) is shown in two examples, but the information indicating the encoding type is stored in the MSB of Q bits, and the run is stored in the remaining Q-1 bits. It may be used as a region.

  In the embodiment, the run-length encoding process is performed according to the procedure shown in FIG. 1, but the type of encoding is not limited to this. That is, any code may be used as long as it dynamically changes or updates the parameters. For example, the run RL may be applied to the Golomb coding using the dynamic parameter K.

[Second Embodiment]
In the first embodiment, the parameters J and K are determined with reference to the parameter specifying information (run in the first embodiment) of the history information of the pixel one line before the target pixel Xi. However, the run index value of the pixel one line before the target pixel Xi may be applied as the run index value when the target pixel is run-length encoded.

  In this case, in step S912 of FIG. 9, the array variable D (x, 1) may store not the run but the variable J that is the updated line index value when run-length encoding is performed. .

  Further, in step S903 in FIG. 9, the run index value may be acquired from D (x, 1) and determined as the value of the parameter J. When the parameter J is determined, the parameter K can be uniquely determined from the table of FIG.

[Third Embodiment]
In the third embodiment, an example will be described in which the run index value to be referred to is changed using region information for an image created by combining a plurality of images.

  For example, in the case of an image having two types of attributes for which foreground and background area information is given, the foreground and the background are encoded separately. Since the value of the run index varies depending on the image area, an optimum run index value can be assigned when the run index is dynamically followed.

  Specifically, in the case of the image as shown in FIG. 7, the gray portion has the foreground image attribute and the others have the background image attribute. The background image is a solid white image, and the improvement of the encoding efficiency by the run-length encoding method is expected. Also for the foreground image, since the run length does not fluctuate extremely, the encoding efficiency can be improved.

  In order to realize this, when the image is raster-scanned and encoded, the attribute of each pixel (one bit is sufficient if switching between two attributes) is input, and based on the information indicating the input attribute The history information to be referred to may be switched. Specifically, it may be expressed by three arguments such as an array variable D (x, C, Atr), the variable Atr is regarded as an attribute, and two types of history information may be used.

  As a result, when the line following the last line in one natural image block shown in FIG. 7 is encoded, the encoding history information of the line immediately before the first line of the natural image block is encoded. Can also be referred to.

  As the image data to be encoded, an image obtained by receiving and rendering print data in PDL format is suitable. The rendering unit that performs the rendering process draws a character pattern or a line drawing in the page memory based on the print data, and develops a natural image included in the print data in the page memory. Accordingly, the rendering unit includes an attribute memory corresponding to the page memory. When the rendering of one page is started, all pixels are initialized in the attribute memory as having a character / line drawing attribute. After that, when the natural image is expanded in the page memory, the attribute of the corresponding area in the attribute memory may be rewritten to indicate the natural image. Then, when the rendering unit finishes rendering one page, the image data in the page memory and the data in the attribute memory may be output to this apparatus. As a result, the attribute can be discriminated for each pixel, and the encoding parameter can be switched for each attribute.

  In the above embodiment, the size of image data to be encoded is set to the number of pixels W in the horizontal direction and the number of pixels H in the vertical direction, and the image data is encoded by raster scanning. However, from this image data, a block of m × n (m, n is a value of 2 or more) pixels set by the user using an operation unit (not shown) may be input and encoded. In this case, it is only necessary to encode each block unit by replacing W with m and H with n.

[Other Embodiments]
In the first and second embodiments, the run length encoding is performed by referring to the run length of the pixel one line before the target pixel and the run index value. It does not have to be a pixel before the line.

  For example, in the case of an image as shown in FIG. 10, when run length coding is performed on a white pixel, the run index value is referred to by referring to the run length or run index value of the previous pixel as in the first embodiment. Is determined, the optimal run index value is not assigned, and the amount of codes may increase. In the case of such an image, the run length or run index that appears for the first time and the run length or run index that appears for the second time are stored, and fluctuations in the run index value are monitored. Then, it is determined whether or not the length of the reference run or the value of the run index is referred to from a run above the target pixel or from another run. By doing so, the amount of code can be suppressed.

  The embodiment according to the present invention has been described above. In the above-described embodiment, an example has been described in which an application is executed on a general-purpose information processing apparatus such as a personal computer. However, similar processing may be performed by hardware.

  Also, the computer program is usually stored in a computer-readable storage medium such as a CD-ROM, and can be executed by setting it in a reader (CD-ROM drive) and copying or installing the program in the system. become. Therefore, it is clear that such a computer readable storage medium falls within the scope of the present invention.

It is a flowchart which shows the flow of the conventional run length encoding process. It is a figure which shows the correspondence table of a run index value and the parameter K. It is a flowchart which shows the main process of the encoding process of 1st Embodiment. It is a figure which shows the relative positional relationship of the pixel of interest Xi and its vicinity pixel Xa, Xb, Xc, Xd. It is a figure which shows an example of the image of the encoding target in embodiment. FIG. 6 is a diagram illustrating an example of coding history information located in the vicinity of a target pixel in the image of FIG. 5. It is a figure which shows the example of the image which 3rd Embodiment applies. It is a block block diagram of the image coding apparatus of embodiment. It is a flowchart which shows the detail of step S305 of FIG. It is a figure which shows an example of the image of the encoding target of a modification.

Claims (12)

An image encoding device that inputs pixel data in raster scan order and performs run-length encoding according to dynamically updated encoding parameters,
Storage means for storing, for each pixel position, encoding history information for specifying the encoding parameter updated by performing run-length encoding;
An acquisition unit that acquires, from the storage unit, encoding history information of a pixel position of the previous line that is the same as the horizontal position of the target pixel when run-length encoding a run from the position of the target pixel; ,
The encoding parameter specified by the encoding history information acquired by the acquisition unit is set as an initial encoding parameter of the encoding of the run, and the initial encoding parameter is updated according to the run, and the run Encoding means for run-length encoding
Storage means for storing, in the storage means, information specifying the encoding parameter after encoding the run by the encoding means as encoding history information of each pixel constituting the run. An image encoding device characterized by the above.   The image encoding apparatus according to claim 1, wherein the storage unit stores, as the encoding history information, a run to which each pixel belongs for each pixel position.   The image encoding apparatus according to claim 1, wherein the storage unit stores, as the encoding history information, an updated encoding parameter when run-length encoding is performed for each pixel position. A control method for an image encoding device that inputs pixel data in raster scan order and performs run-length encoding according to dynamically updated encoding parameters,
Securing a storage area in the memory for storing, for each pixel position, encoding history information for specifying the encoding parameter updated by performing run-length encoding;
An acquisition step of acquiring, from the storage area, encoding history information of the pixel position of the previous line that is the same as the horizontal position of the target pixel when the run from the position of the target pixel is run-length encoded; ,
The encoding parameter specified by the encoding history information acquired in the acquisition step is set as an initial encoding parameter of the encoding of the run, and the initial encoding parameter is updated according to the run, and the run An encoding step for run-length encoding
A storage step of storing, in the storage area, information specifying the encoding parameter after encoding the run by the encoding step as encoding history information of each pixel constituting the run. A control method for an image encoding device characterized by the above.   A computer program that causes a computer to function as the image encoding device according to any one of claims 1 to 3 when the computer reads and executes the computer program. An image encoding device that inputs pixel data in raster scan order and performs run-length encoding or predictive encoding according to dynamically updated encoding parameters,
Encoding history information represented by identification information indicating whether the encoding is performed by run-length encoding or predictive encoding, and specific information for specifying the encoding parameter updated by performing run-length encoding Storage means for storing for each pixel position;
Determining means for determining whether or not the number of colors represented by a plurality of already encoded pixels located in the vicinity of the pixel of interest is equal to or less than a preset threshold value;
A run length encoding means for detecting a run from the pixel of interest and performing a run length encoding on the detected run when the determination means determines that the number of colors is equal to or less than the threshold;
When the determination unit determines that the number of colors exceeds the threshold, the storage unit stores encoding history information including identification information indicating that the pixel of interest is prediction-encoded and the pixel of interest is prediction-encoded. Predictive encoding means stored in
The run-length encoding means is
An acquisition unit that acquires, from the storage unit, encoding history information of the pixel position of the previous line that is the same as the horizontal position of the target pixel when the run from the position of the target pixel is run-length encoded. When,
When the identification information included in the encoding history information acquired by the acquisition means indicates run-length encoding, the encoding parameter specified by the parameter specifying information included in the acquired encoding history information is initialized. Is determined as an encoding parameter of
When the identification information included in the encoding history information acquired by the acquiring unit indicates predictive encoding, a determining unit that determines a default encoding parameter as an initial parameter;
Encoding means for run-length encoding the run while updating the initial encoding parameters determined by the determining means according to the run;
When the encoding is performed by the encoding means, identification information indicating that the run-length encoding has been performed, and information for specifying the encoding parameter after performing the encoding of the run, configure the run An image encoding apparatus comprising: a storage unit that stores the encoding history information of each pixel position in the storage unit.   The image encoding apparatus according to claim 6, wherein the parameter specifying information stored in the storage unit is a run.   The image encoding apparatus according to claim 6, wherein the parameter specifying information stored in the storage unit is an updated encoding parameter when run-length encoding is performed.   9. The encoding parameter according to claim 6, wherein the default encoding parameter is an updated encoding parameter before the position of the target pixel and last run-length encoding. The image encoding device described. A method of controlling an image encoding device that inputs pixel data in raster scan order and performs run-length encoding or predictive encoding according to dynamically updated encoding parameters,
Encoding history information represented by identification information indicating whether the encoding is performed by run-length encoding or predictive encoding, and specific information for specifying the encoding parameter updated by performing run-length encoding Securing a storage area in the memory for storing for each pixel position;
A determination step for determining whether or not the number of colors represented by a plurality of already encoded pixels located in the vicinity of the pixel of interest is equal to or less than a preset threshold;
If it is determined in the determination step that the number of colors is equal to or less than the threshold value, a run length encoding step of detecting a run from the target pixel and performing a run length encoding on the detected run;
When it is determined in the determination step that the number of colors exceeds the threshold, the target pixel is predictively encoded, and at the same time, identification information indicating that the target pixel has been predictively encoded is stored in the storage area. A process,
The run length encoding step includes:
An acquisition step of acquiring, from the storage area, encoding history information of the pixel position of the previous line that is the same as the horizontal position of the target pixel when the run from the position of the target pixel is run-length encoded. When,
When the identification information included in the encoding history information acquired in the acquisition step indicates run-length encoding, the encoding parameter specified by the parameter specifying information included in the acquired encoding history information is initialized. Is determined as an encoding parameter of
When the identification information included in the encoding history information acquired in the acquisition step indicates predictive encoding, a determination step of determining a default encoding parameter as an initial parameter;
An encoding step for run-length encoding the run while updating the initial encoding parameters determined in the determination step according to the run;
When the encoding is performed by the encoding step, identification information indicating that the run-length encoding has been performed, and information for specifying the encoding parameter after the encoding of the run are configured in the run And a storage step of storing in the storage area as the encoding history information of each pixel to be performed.   A computer program that causes a computer to function as the image encoding device according to any one of claims 6 to 9 when the computer reads and executes the computer program.   A computer-readable storage medium, wherein the computer program according to claim 5 or 11 is stored.

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