JP2012095228A - Image encoding device and control method thereof, and program and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image encoding device suitably encoding both a character line drawing and a gradation image, capable of encoding at high speed, while generating fixed-length encoded data by a block unit.SOLUTION: A first encoding unit 4 performs reversible encoding of a representative pixel value of a pixel belonged to a character line drawing in a target block and identification information for identifying the character line drawing/non-character line drawing in every pixel. A second encoding unit 5 performs irreversible encoding of a block without a high frequency component or with a few high frequency components, of which a pixel value of the pixel belonged to the character line drawing in the target block is displaced by an average value of the pixel belonged to the non-character line drawing. A multiplexing unit 10 multiples encoding data generated by the first and second encoding units. In the case that all pixels in the target block has the same in color, the encoding data corresponding to the case of generation in the first or second encoding unit is generated by a third encoding unit 6, and a multiplexing unit 9 outputs the encoding data generated from the third encoding unit 6.

Description

  The present invention relates to an image data encoding technique.

  Conventionally, Patent Document 1 is known as a method for compressing block-unit image data into a fixed-length code. In this document, a visually important pixel (for example, a character / line image pixel) is extracted from image data in block units and losslessly encoded, and other data is lossyly encoded. That is, a plurality of encoding processes are executed in parallel on one image data.

  Further, Patent Document 2 is known as a method for encoding block unit image data at high speed. Here, in the DCT calculation of JPEG encoding, the calculation value when the pixels of the block are all white is stored in advance. Then, when the block and the immediately preceding block are all white, encoding is performed at high speed by using the stored DCT calculation value.

JP 2008-278042 A Japanese Patent Laid-Open No. 7-30762

  In an apparatus that encodes input image data using at least two encoding methods in parallel, when trying to encode a block of the same color, both of the above two encoding methods are already being executed. Takes time for overall encoding.

  The present invention has been made in view of the above points, and is an apparatus having both encoding suitable for character line drawings and encoding suitable for gradation images, and generates fixed-length encoded data for each block. However, the present invention intends to provide a technique for performing encoding at higher speed.

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 for encoding image data,
Input means for inputting a block composed of a plurality of pixels from an image to be encoded;
Analyzing means for analyzing a pixel value of each pixel in the input target block and determining whether or not there is a pixel belonging to the character line image in the target block;
If the analysis means determines that there are pixels belonging to the character line drawing in the block of interest, the representative pixel value of the character line drawing and identification information indicating whether each pixel belongs to the character line drawing or non-character line drawing Generating means for generating; and
First encoding means for losslessly encoding the representative pixel values and identification information of the character / line image generated by the generating means to generate encoded data of the first format;
When the analysis unit determines that there is a pixel belonging to the character / line drawing in the target block, the pixel value of the pixel belonging to the character / line drawing is replaced with the average pixel value of the pixel belonging to the non-character / line drawing. Replacement means for generating a block composed of pixels;
When the analyzing unit determines that there is a pixel belonging to the character line image in the target block, the analyzing unit determines that there is no pixel belonging to the character line image in the target block. In such a case, the second encoding means for irreversibly encoding the block before replacement by the replacement means and generating encoded data of the second format;
The encoded data generated by the first encoding unit and the second encoding unit are multiplexed, and the presence or absence of the encoded data of the first format in the block header, the second Multiplex means for generating and outputting fixed-length block encoded data storing information indicating the presence or absence of encoded data in a format;
Determination means for determining whether or not the pixel values of all pixels of the block of interest input by the input means are the same;
When the determination means determines that all the pixels of the block of interest have the same pixel value, the encoding of the block of interest by the first encoding means and the second encoding means is stopped and stored in advance. From the encoded data of the first and second formats and the pixel value of the block of interest in which all the pixels are the same, either the encoded data of the first format or the encoded data of the second format Third encoding means for generating either one of
When the determining unit determines that all the pixels of the target block have the same pixel value, the multiplexing unit converts the encoded data obtained from the third encoding unit into the encoded data of the target block. Is output as

  According to the present invention, there is provided an apparatus having both encoding suitable for a character / line image and encoding suitable for a gradation image, while generating fixed-length encoded data in units of blocks and performing encoding. It becomes possible to perform at higher speed.

1 is a configuration diagram of an image encoding device according to a first embodiment. The figure which shows the image coding format in 1st Embodiment. The block diagram of the image coding apparatus in 2nd Embodiment. The figure which shows the flowchart of the image coding process in 3rd Embodiment.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings.

[First Embodiment]
In the following description, the source of multi-value image data to be encoded is an image scanner, but it may be a storage medium storing image data, and the type thereof is not limited. For the sake of simplicity, the description will be made assuming that the image data to be encoded is a monochrome image of one component per pixel, and that the component is 8 bits (256 gradations) and represents luminance. However, the number of color components and the type of color space (RGB, CMY, Lab, etc.) may be arbitrary, and the number of bits of one color component is not limited to 8 bits. Incidentally, when one pixel is composed of a plurality of components, the items described below may be executed for each component.

  FIG. 1 shows a configuration diagram of an image coding apparatus according to the first embodiment of the present invention. This apparatus includes a control unit 11 that controls the entire apparatus and the following processing units.

  The blocking unit 1 generates block image data composed of a plurality of pixels (m × n pixels) from the image data to be encoded. In the following, for simplification, the size of one block is 8 × 8 pixels.

  The analysis unit 2 analyzes the image data for one block (8 × 8 pixels in the embodiment) input from the blocking unit 1 and belongs to each of the character line drawing / non-character line drawing for each pixel in the block. Identification data indicating these and pixel values determined to belong to the character line drawing (representative color of the character line drawing) are generated and output to the first encoding unit 4. A specific example is as follows.

  The analysis unit 2 calculates an average pixel value AVE of all the pixels in the block, a pixel group having a pixel value larger than the average pixel value AVE (hereinafter referred to as a first pixel group), and the average pixel value AVE. The pixel groups are classified into the following pixel groups (hereinafter referred to as second pixel groups). Then, a first average pixel value AVE1 that is an average pixel value of the first pixel group and a second average pixel value AVE2 that is an average pixel value of the second pixel group are obtained, and the difference between them is “AVE1−AV2”. Whether or not exceeds a preset threshold value Th1. If the threshold Th1 is exceeded, the second pixel group having low luminance (high density) is determined as a pixel group belonging to a character line drawing, and the first pixel group is determined to belong to a pixel group belonging to a non-character line drawing. To do. In this case, the second average value AVE2 is determined as the representative pixel value belonging to the character / line image. Then, the inside of the block is raster-scanned to generate 1-bit identification data of “1” for the pixels belonging to the character / line image and “0” for the pixels belonging to the non-character / line image. In the embodiment, since one block has 8 × 8 pixels, 64 pieces of identification data are generated from one block. Hereinafter, 64 pieces (64 bits) of identification data for one block are referred to as identification information. If {AVE1-AV2}> Th1, the analysis unit 2 outputs the representative pixel value of the character / line image + identification information to the first encoding unit 4 to perform encoding thereof, and causes the multiplexing unit 10 to perform encoding. In contrast, a signal indicating that the representative pixel value of the character / line image and the encoded data of the identification information are multiplexed with respect to the block of interest. On the other hand, if {AVE1-AV2} ≦ Th1, the representative pixel value of the character / line image + identification information is not output to the first encoding unit 4, and the representative pixel of the character / line image is output to the block of interest. The multiplexing unit 10 is notified that there is no encoded data of value and identification information. Furthermore, the result of detection by the same color detection unit 3 described later is also notified to the multiplexing unit 10. The above is a case where the pixel value indicates luminance. When the pixel value indicates density, AVE1 is used as the representative pixel value of the character / line image.

In addition to the above processing, the analysis unit 2 outputs the input block data to the second encoding unit 5 as it is when {AVE1-AVE2} ≦ Th1. If {AVE1-AVE2}> Th1, the pixels belonging to the non-character line drawing in the input block remain at the pixel values, and the pixel values belonging to the character line drawing are equal to the first average value AVE1 (non-character line drawing). The new block data replaced with the average value of the pixels belonging to (2) is generated and output to the second encoding unit 5. The former case will not be explained. Here, a specific example of the latter will be described. Pout (x, y) is the pixel value of the new block with coordinates x and y (0 ≦ x, y ≦ 7), Pin (x, y) is the pixel value of the input block, and B (x , y), new block data may be generated as follows.
・ When B (x, y) = 0 (when the target pixel is a non-character line drawing)
Pout (x, y) ← Pin (x, y)
When B (x, y) = 1 (when the target pixel is a character line drawing)
Pout (x, y) ← AVE1
As a result, the block data supplied to the second encoding unit 5 has no or little high frequency (AC) component, and a high compression rate is expected when lossy encoding such as JPEG is performed. it can.

  Next, the same color detection unit 3 will be described. The same color detection unit 3 is a processing unit inside the analysis unit 2 and determines whether or not all the pixels constituting the input block have the same color (luminance). When it is determined that the color (pixel value) is determined, the color (pixel value) is output to the third encoding unit 6. Note that the user may set a range for determining “same color”. For example, when the difference between the maximum pixel value and the minimum pixel value in all the pixels in the block is obtained and the difference is less than the allowable range (threshold Th2; where Th2 ≦ Th1) that can be determined as the same color, You may make it determine with all the pixels of a block having the same color.

  The reason that the same color detection unit 3 is provided in the analysis unit 2 is that when it is classified into the first pixel group and the second pixel group described above, it can be determined as a subordinate. Because. That is, the maximum value and the minimum value of the pixel values of all the pixels are obtained, and if the difference is 0 or less than the threshold value indicating the allowable range, they can be regarded as the same color (in the latter case, the average value AVE is the character value). It may be a representative value of line drawing).

  When the same color detection unit 3 determines that all the pixels in the target block have the same color, the analysis unit 2 sends the first encoding unit 4 and the second encoding unit 5 to the target block. Is not supplied (that is, encoding of the block of interest by the first and second encoding units is stopped). The third encoding unit 6 generates encoded data when the same color detecting unit 3 determines that all pixels in the block of interest have the same color.

  The first encoding unit 4 receives a representative color (8 bits) of character / line drawing and identification information (64 pieces of identification data = 64 bits), and performs lossless encoding such as run-length encoding on the identification information. Then, the run-length encoded data of the character / line drawing representative color (8 bits) + identification information is output to the buffer 7.

  The second encoding unit 5 inputs block data in which the pixel value of the character / line image is replaced with the average value AVE1 of the pixel values of the non-character / line image, or input block data (block data before replacement), and inputs the JPEG Encoding (lossy encoding) is performed to generate encoded data of DC component + AC component and output to the buffer 8. It can be understood that a high compression ratio can be obtained because there is no or little high-frequency component.

  The third encoding unit 6 generates the encoded data only when the information from the same color detection unit 3 has the same color for all the pixels of the block of interest, and outputs the encoded data to the buffer 9. There are two types of formats of encoded data generated by the third encoding unit 6.

  The first is encoded data corresponding to the case where all the pixels are considered to belong to the character / line image in the first encoding unit 4 “pixel value representing the representative color of the character / line image + EOB (End of Block)”. Block) ”. Since all the pixels are the same, it is easy to understand that EOB has an equivalent meaning to a code word indicating that the run is 64. Basically, only the EOB code word stored in advance is added to the pixel value indicated as the same color from the same color detection unit 3 and output, and it is not necessary to scan the pixel value. Only the processing time can be very short. Hereinafter, the encoded data of this format is referred to as first format encoded data.

  Another type of encoded data is “DC component + AC component encoded data”, which is an encoding format when the second encoding unit 5 encodes a block in which all pixels have the same color value. It is. All the pixels in the block of interest are assigned to the “DC component” a pixel value representing a color that is determined to be the same color by the same color detection unit 3. Since it is promised that there will be no AC component, or very few, the EOB codeword is assigned in this embodiment. Hereinafter, the encoded data of this format is referred to as second format encoded data.

  Each time the third encoding unit 6 in the embodiment receives notification from the same color detection unit 3 that the block of interest is the same color, the third encoding unit 6 switches the first and second format encoded data, Generate.

  Upon receiving the analysis result from the analysis unit 2, the multiplexing unit 10 combines the encoded data from the buffers 7 to 9, and generates and outputs block encoded data of fixed length L with the block header at the head. . Here, the format of the encoded data for one block generated by the multiplexing unit 10 will be described. The lower limit of the fixed length L is 8 bits representing the representative pixel value of the character / line image + the worst code length (number of bits) of the identification information + 8 bits of the DC component generated by the second encoding unit. The fixed length is set by the user. Information indicating the fixed length may be stored in the file header.

  2A to 2D show types of fixed-length encoded data for one block generated by the multiplexing unit 10 in the present embodiment. In the header, the multiplexed data only needs to indicate the presence / absence of the encoded data by the first and second encoding units, and therefore includes 2 bits indicating it.

  FIG. 2A shows an encoded data format when it is determined that the detection result of the same color detection unit 3 also shows non-identical colors and that a pixel of a character line drawing exists in the block of interest. As shown in the figure, the encoded data stored in the buffer 7 and the encoded data stored in the buffer 8 are arranged after the header. If the encoded data of all AC components stored in the buffer 8 cannot be stored, bits exceeding the fixed length L are discarded. In this case, there is a possibility that an incomplete code word exists at the end position of the fixed length, but when there is an incomplete code word exceeding the fixed length L on the decoding side, the AC component value after that Since “0” is regarded as being decoded, there is no problem. Even if encoded data of all AC components is stored, if there is still an empty area, appropriate dummy data may be stored.

  FIG. 2B shows the encoded data format when the detection result of the same color detection unit 3 also shows non-identical colors and it is determined that there is no character line drawing pixel in the block of interest. As shown in the figure, the encoded data stored in the buffer 8 is arranged following the header. Note that the bits that exceed the fixed length L are discarded, and the dummy bits that are less than the fixed length L are added in the same way as in FIG.

  2C and 2D show the encoded data format when the detection result of the same color detection unit 3 indicates the same color. As shown in the figure, after EOB, 0 is stored as dummy data in an amount satisfying the fixed length L. The encoded data shown in FIGS. 2C and 2D are alternately switched as described above. The fact that all the pixels in the block are the same color can be easily understood by imagining, for example, the upper, lower, left and right margin areas and line spacing portions of a document image composed of ordinary characters. In the case of such an area, according to the present embodiment, FIGS. 2C and 2D are alternately generated, so that the JPEG decoding process can be executed for the next block during the run-length decoding. The possibility that two decoding processes can be executed in parallel can be increased, and as a result, the decoding process can be speeded up.

  By performing the control as described above, when the same color block is encoded, the encoding is advanced at a high speed by the third encoding process without waiting for the end of the first and second encoding processes. Therefore, it is possible to perform encoding at high speed in encoding of image data including many blocks of the same color.

[Description of modification]
An example will be described below in which the image encoding process in the first embodiment described above is realized by a computer program in which an information processing apparatus such as a personal computer executes a processor therein. The hardware of the information processing apparatus may be general, and will not be described in detail here. However, an example will be described in which image data to be encoded is stored as a file in an external storage device such as a hard disk, and the encoding result is also stored in the external storage device. However, the source of the image data to be encoded may be a storage on the network or an image scanner, and the output destination of the encoding result may be a portable storage medium or a network medium. Absent.

  When the decoding process is started in S1, the processor loads image data for one block from the input file onto the RAM in S2. In S3, the processor analyzes the image data of the loaded target block on the RAM, and extracts data necessary for the first encoding and the second encoding. Details of the analysis are as described in the first embodiment. Next, in S4, it is determined whether the target block is a block composed of the same color image data. If it is not the same color block, the process proceeds to S5. If they are the same color block, the process proceeds to S8.

  In S5, the first encoding is performed. This first encoding is the same as the first encoding unit 4 in the first embodiment. However, similarly to the first encoding unit 4, if there is no character / line drawing pixel in the block of interest, encoded data is not generated. In S6, the second encoding is performed. The details of the second encoding are the same as those of the second encoding unit 5 in the first embodiment. In S7, the encoded data generated in S5 (if any) and the encoded data generated in S6 are output to the external storage device. The format of the encoded data at this time is either one of FIGS.

  On the other hand, when the processing is shifted to S8, the third encoding is performed. The details of the third encoding are the same as those of the third encoding unit 6 in the first embodiment. In step S9, the encoded data is output to the external storage device. The format of the encoded data at this time is either one of FIGS. 2C and 2D.

  In S10, it is determined whether all the image data of the file has been processed. If it is determined that all the image data has not been processed, the processes in and after S2 are repeated. If all the image data has been processed, the process proceeds to S11, and all encoding is completed.

  The time required for execution of the first and second encodings via step 5 and step 6 and the third encoding of step 8 is different. As described in the first embodiment, the third encoding is completed in a short time compared to the first and second encodings that take time. The third encoding can be processed independently of the first and second encodings. Therefore, the third encoding can be performed during the first and second encoding. In that case, the third encoding may end before the first and second encoding. In that case, first, the encoded data processed by the third encoding is output to the external storage device. Since the encoded data of the present invention is fixed-length encoded data, the external address of the output destination can be known in advance. By associating the address of the external storage device of the output destination with the address on the external storage device of the input block, even if the order of input and output is different, there is no doubt that the external storage device will encode the predetermined address It becomes possible to output converted data.

  By performing the control as described above, the same operational effects as those of the first embodiment can be obtained even when implemented by a computer program.

[Second Embodiment]
In the second embodiment, an example will be described in which encoded data that can efficiently use the decoding resources of the first format encoded data and the second format encoded data on the decoding side is described. Specifically, the decoding process is prevented from being biased to one of the run-length decoding process and the JPEG decoding process.

  FIG. 3 shows a configuration diagram of an image encoding device according to the second embodiment. The processing units that perform the same operations as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. A processing unit that performs operations peculiar to the second embodiment will be described.

  The third encoding unit 24 is an encoding unit that encodes blocks detected as the same color by the same color detection unit 3. The third encoding unit 24 generates first format encoded data (character / line image representative pixel value + EOB). That is, encoded data having a format shown in FIG.

  The fourth encoding unit 25 is an encoding unit that encodes blocks detected as the same color by the same color detection unit 3. The fourth encoding unit 25 generates second format encoded data (DC component value + EOB). That is, encoded data having the format shown in FIG.

  The comparison unit 23 has two registers (or counters) inside, and is cleared to zero at the start of the encoding process. One register is used for counting the number of times the encoded data is output to the buffer 7, and the other register is used for counting the number of times the encoded data is output to the buffer 8. If the target block contains character / line image pixels, the encoded data is stored in both the buffers 7 and 8 from the target block, so that each register is counted up by “1”. . If there is no character / line image pixel in the block of interest, but the same color, the block of interest stores only the encoded data of the second encoding unit 5 in the buffer 8. Only the number of times the digitized data is output is counted up.

As described above, the comparison unit 23 sets the number of output times of the encoded data of the first encoding unit 4 from the start of the encoding of the image to the present as N1, and the encoded data of the second encoding unit 5 When the number of outputs is N2,
Condition: N1 ≦ f (N2)
If the condition is satisfied, a control signal of “0” is output to the selection unit 26. Otherwise, the control signal of “1” is output. In general, JPEG encoding and decoding require a large amount of calculation for DCT conversion (matrix calculation). On the other hand, processes related to run-length encoding and decoding are not as heavy as DCT processes. The function f () is a function for canceling the weight of the calculation amount. For simplicity, a preset coefficient R may be defined and determined under the following conditions.
Condition: N1 <R × N2

  The selection unit 26 selects which of the encoded data of the third encoding unit 24 or the fourth encoding unit 25 is to be output to the buffer 27. This selection is determined based on a control signal from the comparison unit 23. That is, when the control signal of the comparison unit 23 is “0”, the encoded data of the third encoding unit 24 is output to the buffer 27, and when “1”, the encoding of the fourth encoding unit is performed. The data is output to the buffer 27. By operating in this way, when the same color block is input, the encoded data of the format with the smaller number of outputs to the buffers 7 and 8 is stored in the buffer 27. As a result, in a decoding apparatus that can execute run-length decoding and JPEG decoding in parallel, it is possible to suppress that the encoded data to be decoded is supplied to one of them, in other words, resources for these decoding processes are reduced. It can operate efficiently, and as a result, the decoding process can be speeded up.

  In the above description, the comparison unit 23 has two registers (or counters) inside, and each of them holds the number of times encoded data is output to the buffer 7. However, the present invention is not limited to this. For example, the buffers 7 and 8 are FIFO memories, and the used words are monitored by comparing used words. For example, the used words are simply compared, and the smaller the used words are determined to have a lower occupation rate. Alternatively, if the FIFOs have different FIFO full capacities, the used word empty word numbers are compared to determine that the one with the larger empty word number has a lower occupation rate. Alternatively, the used word is divided by the FIFO full capacity used word (literally calculating the occupation ratio), and the smaller value is determined to be the lower occupation ratio. In this way, the comparison unit 23 compares the occupancy rates of the buffers 7 and 8, and outputs 0 when the occupancy rate of the buffer 7 is smaller than that of the buffer 8, and outputs 1 otherwise. It doesn't matter.

(Other examples)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

An image encoding device for encoding image data,
Input means for inputting a block composed of a plurality of pixels from an image to be encoded;
Analyzing means for analyzing a pixel value of each pixel in the input target block and determining whether or not there is a pixel belonging to the character line image in the target block;
If the analysis means determines that there are pixels belonging to the character line drawing in the block of interest, the representative pixel value of the character line drawing and identification information indicating whether each pixel belongs to the character line drawing or non-character line drawing Generating means for generating; and
First encoding means for losslessly encoding the representative pixel values and identification information of the character / line image generated by the generating means to generate encoded data of the first format;
When the analysis unit determines that there is a pixel belonging to the character / line drawing in the target block, the pixel value of the pixel belonging to the character / line drawing is replaced with the average pixel value of the pixel belonging to the non-character / line drawing. Replacement means for generating a block composed of pixels;
When the analyzing unit determines that there is a pixel belonging to the character line image in the target block, the analyzing unit determines that there is no pixel belonging to the character line image in the target block. In such a case, the second encoding means for irreversibly encoding the block before replacement by the replacement means and generating encoded data of the second format;
The encoded data generated by the first encoding unit and the second encoding unit are multiplexed, and the presence or absence of the encoded data of the first format in the block header, the second Multiplex means for generating and outputting fixed-length block encoded data storing information indicating the presence or absence of encoded data in a format;
Determining means for determining whether or not colors represented by pixel values of all pixels of the block of interest input by the input means are the same;
When the determination means determines that all pixels of the block of interest have the same color, the encoding of the block of interest by the first encoding means and the second encoding means is stopped and stored in advance. From the encoded data of the first and second formats in which all pixels have the same color and the pixel value of the block of interest, the encoded data of the first format or the encoded data of the second format Third encoding means for generating any one of them,
When the determining unit determines that all pixels of the target block have the same color, the multiplexing unit uses the encoded data obtained from the third encoding unit as the encoded data of the target block. An image encoding apparatus that outputs the image. The analysis means includes
An average pixel value AVE of all pixels is calculated in the target block,
Classifying into a first pixel group having a pixel value exceeding the calculated average pixel value AVE and a second pixel group having a pixel value less than or equal to the average pixel value AVE;
When the difference between the average pixel value AVE1 of the pixels belonging to the first pixel group and the average pixel value AVE2 of the pixels belonging to the second pixel group exceeds a preset threshold, there is a character / line image in the block of interest. If it does not exceed the preset threshold, it is determined that there is no character line drawing in the block of interest,
The analysis means determines the average pixel value AVE2 as a representative pixel value belonging to a character line image when the pixel value indicates luminance, and determines the average pixel value AVE1 as a character line image when the pixel value indicates density. The image encoding device according to claim 1, wherein the image encoding device is determined as a representative pixel value belonging to the image data.   The third encoding means switches and generates the encoded data of the first and second formats each time the determination means determines that all pixels of the block of interest have the same color. The image encoding device according to claim 1 or 2. Further, a counting means for counting N1 of the number of times that the encoded data is generated by the first encoding means, and N2 of the number of times that the encoded data is generated by the second encoding means,
N1 and N2 counted by the counting means and a preset weight function f () are:
Condition: N1 <f (N2)
The third encoding means generates encoded data of the first format when the condition is satisfied, and generates encoded data of the second format when the condition is not satisfied. The image coding apparatus according to claim 1 or 2.   The determination means determines that all pixels in the block of interest have the same color when the difference between the maximum pixel value and the minimum pixel value of all pixels of the block of interest is equal to or less than a preset threshold value. The image encoding device according to claim 1, wherein the image encoding device is a video encoding device.   6. The image code according to claim 1, wherein the first encoding unit is a run-length encoding unit, and the second encoding unit is a JPEG encoding unit. Device.   A computer program that causes a computer to function as each unit of the image encoding device according to claim 1 by being read and executed by a computer.   A computer-readable storage medium storing the computer program according to claim 7. A control method for an image encoding device for encoding image data, comprising:
An input step in which an input means inputs a block composed of a plurality of pixels from an image to be encoded;
An analyzing step of analyzing a pixel value of each pixel in the input target block and determining whether or not there is a pixel belonging to the character line image in the target block;
When the generating unit determines that the analysis step includes a pixel belonging to the character line drawing in the target block, the representative pixel value of the character line drawing and whether each pixel belongs to the character line drawing or the non-character line drawing are determined. A generating step for generating identification information to indicate;
A first encoding step, wherein the first encoding means losslessly encodes the representative pixel value and identification information of the character / line drawing generated in the generation step, and generates encoded data of the first format;
When the analyzing unit determines that the pixel belonging to the character line drawing is in the target block, the pixel value of the pixel belonging to the character line drawing is replaced with the average pixel value of the pixels belonging to the non-character line drawing, A replacement step for generating a block composed of non-character line drawing pixels;
When the second encoding means determines that the analysis step includes a pixel belonging to the character / line image in the target block, the analysis step uses the block obtained in the replacement step as the character in the target block. A second encoding step of irreversibly encoding the block before replacement by the replacement step when it is determined that there is no pixel belonging to the line drawing, and generating encoded data of the second format;
The multiplexing means multiplexes the encoded data generated in the first encoding step and the second encoding step, and the presence or absence of the encoded data of the first format in the block header And a multiplexing step for generating and outputting fixed-length block encoded data storing information indicating the presence or absence of encoded data in the second format, and
A determining step for determining whether or not the colors represented by the pixel values of all the pixels of the block of interest input in the input step are the same;
When the third encoding means determines that all pixels of the block of interest have the same color in the determination step, the encoding of the block of interest by the first encoding step and the second encoding step From the encoded data of the first and second formats and the pixel value of the block of interest, in which all pixels stored in advance have the same color, or the encoded data of the first format, or the A third encoding step for generating any one of the second format encoded data,
In the multiplexing step, when it is determined in the determination step that all pixels of the target block have the same color, the encoded data obtained from the third encoding step is used as the encoded data of the target block. A control method for an image encoding device, characterized by:

Images