JP5520099B2 - Image processing apparatus and control method thereof - Google Patents

Description

  The present invention relates to an image processing technique, and more particularly to an image compression coding technique.

  In order to realize more efficient compression in the image compression coding technique, a technique has been proposed in which one image is divided into a plurality of tile images and the compression method is switched in accordance with the contents of each tile image. However, for example, when tile images compressed by two types of compression methods, lossless encoding and lossy encoding, are mixed in one image, when the images are decoded (restored), In some cases, an extreme change in image quality is perceived by the user as a visual deterioration at the boundary of. Therefore, Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for controlling to fix to either one of lossless encoding and lossy encoding when a specific image region is encoded.

JP 2008-42683 A

  However, when tile images compressed by two types of compression methods, lossless encoding and lossy encoding, are adjacent, or tile images compressed at different compression rates are adjacent, visual degradation It is easy for the user to perceive. In particular, extreme changes in image quality can be perceived at the boundaries between tile images.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an image compression technique capable of reducing visual deterioration while realizing efficient image compression.

In order to solve one or more problems described above, the image processing apparatus of the present invention has the following configuration. That is, in an image processing apparatus that compresses and encodes image data, input means for inputting image data in units of tile image data that is a pixel block of a predetermined size, and the input tile image data are losslessly encoded and lossless encoded data First encoding means for generating a second encoding for generating lossy encoded data by irreversibly encoding input tile image data by interposing a quantization process according to a quantization step And the lossless encoded data generated by the first encoding unit for the target tile image data and the irreversible encoded data generated by the second encoding unit for the target tile image data The first determination means for determining which data amount is small, and one of the lossless encoded data and the lossy encoded data is determined as the target tag. And selection means you select output as encoded data of Le image data, each time the output select encoded data of the tile of interest image data, in preparation for the encoding of the subsequent tile image data, the quantization When the update means for updating the step and the quantization step set when the target tile image data is irreversibly encoded are equal to or smaller than a second threshold corresponding to a compression rate smaller than the predetermined maximum compression rate For the tile image data subsequent to the tile image data of interest, the encoded data determined by the first determination unit as having a small amount of data are selected and output according to the determination result of the first determination unit. controlling said focused quantization step tile image data has been set upon lossy encoding, it is larger than the second threshold value, the interest tile image data For tile image data subsequent to includes a control means for controlling the pre-hexene-option means to select the lossy encoded data generated by forcibly said second encoding means output, a.

  According to the present invention, it is possible to provide an image compression technique that can reduce visual deterioration while realizing efficient image compression.

1 is a block diagram of an image processing apparatus according to a first embodiment. It is a detailed block diagram of the encoding process part which concerns on 1st Embodiment. It is an operation | movement flowchart of the encoding process part which concerns on 1st Embodiment. It is a flowchart of the parameter control process which concerns on 1st Embodiment. It is a figure which shows the transition state of the parameter of the encoding process part which concerns on 1st Embodiment. It is a flowchart of the parameter control process which concerns on 2nd Embodiment. It is a figure which shows the transition state of the parameter of the encoding process part which concerns on 2nd Embodiment. It is a figure explaining a semi-transparent object.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are merely examples, and are not intended to limit the scope of the present invention.

(First embodiment)
The first embodiment of the image processing apparatus according to the present invention includes a first encoding unit that performs lossless encoding of input data and a second encoding unit that performs lossy encoding of input data. An image processing apparatus including an encoding processing unit will be described below as an example.

<Device configuration>
FIG. 1 is a block diagram of an image processing apparatus 100 according to the first embodiment.

  A data control unit 101 processes input image data. The data control unit 101 includes an encoding processing unit 109 and a decoding processing unit 110. The encoding processing unit 109 is a processing unit that compresses image data and outputs compressed image data. The decoding processing unit 110 is a processing unit that decompresses the compressed image data and outputs the image data. Then, the data control unit 101 stores the output processed image data or compressed image data in the data storage unit 105. The data control unit 101 is controlled by the CPU 103 and the RAM 104. The CPU 103 may be configured to implement the data control unit 101 by executing a predetermined image processing program.

  The data input unit 102 is a functional unit that inputs image data or compressed image data from an external device. The data input unit 102 includes, for example, an image scanner that reads a document and generates image data, and a network interface that receives image data from an external device via a network. The image data includes print data in a printer description language (PDL) format. The data output unit 111 is a functional unit that outputs image data or compressed image data processed by the data control unit 101 to an external device. The data output unit 111 includes, for example, a printer that forms an image on a print medium and a monitor that displays the image.

  The data storage unit 105 stores parameters 106 used for the operation of the image processing apparatus 100, various applications 107 used in the image processing apparatus 100, an operating system (OS) 108, and the like.

  FIG. 2 is a detailed block diagram of the encoding processing unit 109 according to the first embodiment. The encoding processing unit 109 includes a first encoding unit 201, a second encoding unit 202, an encoded data selection unit 203, and a parameter control unit 204.

  In the following description, the data input unit 102 converts image data generated by an external device such as a PC into M × N pixels (M and N are natural numbers) that are processing units of image data in the encoding processing unit 109. It is assumed that the image data is sequentially input. More specifically, the tile is a pixel block of a predetermined size (8 × 8 pixels) obtained by dividing the image data into line image data having a width of 8 pixels and further dividing the line image data every 8 pixels. Input as image data.

  The first encoding unit 201 is a lossless encoding unit that performs lossless encoding and generates lossless encoded data. Since it is lossless encoding, the expansion (decoding) result is the same as that of the original image before encoding, and in principle there is no deterioration in image quality. However, there is no parameter setting for controlling the compression rate. Hereinafter, a case where the first encoding unit 201 uses JPEG-LS encoding (hereinafter simply referred to as LS compression) will be described.

  The second encoding unit 202 is an irreversible encoding unit that performs lossy encoding and generates lossy encoded data. In lossy encoding, compression (encoding) processing is performed on target image data according to a predetermined parameter that affects the compression rate. Hereinafter, a case where the second encoding unit 202 uses JPEG encoding (JPEG compression) will be described. Then, it is assumed that a quantization process according to a quantization step equal to or lower than a first threshold (thus described below Th1) corresponding to a predetermined maximum compression ratio, which is a predetermined parameter affecting the compression ratio, is interposed.

  Note that LS compression, which is lossless encoding, has a completely different algorithm from JPEG compression, which is lossy encoding. LS compression is a technology suitable for character line drawing and computer graphics. In the case of these images, although it is lossless encoding that does not cause image degradation, it is more irreversible than JPEG compression that is lossy encoding. Much less encoded data can be generated. In JPEG compression, 8 × 8 pixel tile image data is converted into frequency domain data, quantized using a quantization step specified by a quantization table (Q-table), and Huffman coding processing is performed. Do. JPEG compression is a technique suitable for photographs and natural images. In the case of these images, much less encoded data can be generated than LS compression, which is lossless encoding. It should be noted that information (such as an identification bit) that can be identified by which encoding method is added to the encoded data output by the first encoding unit 201 and the second encoding unit 202. It shall be.

  The encoded data selection unit 203 outputs the encoded data output from the first encoding unit 201 and the second encoding unit 202 with respect to the tile image data currently processed (the tile image data of interest). Compare the data amount with the encoded data. Then, based on a threshold value (lookup table (LUT)) set by the parameter control unit 204, which tile image data is selected is determined. The selected encoded data is written into the data storage unit 105 or output to the data output unit 111. It should be noted that the encoded data information (encoding type, compression rate, etc.) selected for the tile image data currently processed by the encoded data selection unit 203 is notified to the parameter control unit 204.

  The parameter control unit 204 controls the quantization step used for JPEG compression in the second encoding unit 202 and the LUT used when comparing the data amount in the encoded data selection unit 203.

More specifically, the parameter control unit 204 executes the following four processes.
Compression result feedback processing: Control processing to the second encoding unit 202 for controlling the parameters of the subsequent tile image data based on the compression result of the tile image data currently being processed.
Quantization step control processing: Quantization step control processing used for JPEG compression in the second encoding unit 202. This is a process for reducing a change in image quality that occurs when different compression rates are used between adjacent tile images, and will be described in detail later.
JPEG compression encoded data forced selection process: When the quantization step is larger than a predetermined second threshold (Th2 described later), the encoded data selection unit 203 is forced to perform the second encoding (JPEG compression). This is a process of setting the LUT so as to select compressed encoded data. This is a process for preventing an LS-compressed tile image (that is, non-degraded) from appearing in a JPEG-compressed tile image at a high compression rate.
Parameter initialization processing: Parameters (here, quantization step and LUT) to be executed every time line image data is processed, that is, after the encoding processing for the last tile image data of each line image data is completed. It is an initialization process. This is a process for preventing the processing result of the tile image data processed immediately before (the tile image data at the end of the adjacent line image data) from affecting the tile image data at the head of the line image data. It is.

Furthermore, the following three threshold values (Th0, Th1, Th2) are held regarding the compression rate corresponding to the quantization step designated to the parameter control unit 204 and the second encoding unit 202.
Th0: The lowest compression rate (lower limit compression rate) that can be specified in the second encoding unit 202.
Th1: A compression rate (upper limit compression rate) in which image deterioration due to JPEG compression is not noticeable.
Th2: A compression rate at which the tile image boundary is not noticeable even when adjacent to the LS compressed image.
Note that Th0 <Th2 ≦ Th1 (if Th1 = Th2, there are substantially two threshold values). The image processing apparatus 100 may be configured so that the user sets these three threshold values in advance.

<Operation of the device>
FIG. 3 is an operation flowchart of the encoding processing unit according to the first embodiment.

  In step S201, the data input unit 102 divides image data received from an external device and generates a plurality of tile image data.

  In step S202, one tile image data is set as processing target tile image data (target tile image data), and the first encoding unit 201 and the second encoding unit 202 execute the encoding process. Generate encoded data of a kind. The second encoding unit 202 performs an encoding process based on the quantization step specified at that time. More specifically, a quantization step that is a preset initial value is used for the first tile image data of the line image data, and a control process (to be described later) is performed for other tile image data (S204). Use the quantization step controlled by.

  In step S <b> 203, the encoded data selection unit 203 determines which tile image data of the two types of encoded data is selected based on the LUT set by the parameter control unit 204. More specifically, encoded data with a small amount of data is selected (first determination means), but if the LUT specifies “forced JPEG mode” to be described later, the second encoding unit 202 is selected. The encoded data output from is selected (encoded data selecting means). That is, when the quantization step is equal to or smaller than the second threshold value, encoded data with a small data amount is selected.

  In step S <b> 204, the parameter control unit 204 controls the quantization step in the second encoding unit 202 and the LUT in the encoded data selection unit 203. Details of the operation will be described later.

  In step S205, the CPU 103 determines whether unprocessed tile image data remains among the plurality of tile image data generated in step S201. If it remains, the next tile image data is selected and the process proceeds to step S202. If unprocessed tile image data does not remain, that is, if processing has been completed for all tile image data, the processing ends.

  FIG. 4 is a flowchart of parameter control processing according to the first embodiment. FIG. 4A shows the entire control process, and FIG. 4B shows the detailed process of the determination process (S303). The following processing is realized by the CPU 103 loading the application 107 stored in the data storage unit 105 into the RAM 104 and executing it.

  In step S301, it is selected whether or not the encoded data (that is, JPEG compression) output from the second encoding unit 202 in step S203 has been selected. If JPEG compression is selected, the process proceeds to step S302. If LS compression is selected, the parameter is not changed (S304), and the parameter control process is terminated.

  In step S302, it is determined whether or not the JPEG compression in step S203 is based on a “forced JPEG mode” described later. Specifically, the determination may be made by confirming the currently set LUT, or may be made by referring to a separately generated flag. If it is “forced JPEG mode”, the process proceeds to step S303. If it is not “forced JPEG mode”, the quantization step is shifted to the high compression side by a predetermined amount and updated (S305), and the parameter control process is terminated.

  In step S305, if the quantization step is shifted by a predetermined amount to the high compression side and the compression rate exceeds the threshold value (Th2), “forced JPEG mode” is set. The “forced JPEG mode” is a mode for controlling the LS compression not to be selected for the tile image data immediately after the tile image data to be processed (the tile image data of interest).

  In step S303, the parameter control unit 204 determines an optimal compression method for the tile image data to be processed (target tile image data). In other words, when a quantization step (initial quantization step) that is a preset initial value is used, it is determined which tile image data of two types of encoded data has been selected (second determination means). That is, step S303 is processing for determining an optimal compression method under a certain condition for the tile image data of interest. This is a process necessary for the quantization step in the second encoding unit 202 and the LUT in the encoded data selection unit 203 to be changed by the parameter control process.

  In step S3031, the parameter control unit 204 calculates the data amount of JPEG encoded data when a quantization step that is a preset initial value is used. Specifically, the prediction may be performed based on the data amount of the JPEG encoded data generated in step S202. For example, it can be calculated by multiplying the gain corresponding to the difference between the quantization step value currently specified in the second encoding unit 202 and the above-described initial value. The parameter control unit 204 may have a JPEG compressor having the same logical configuration as that of the second encoding unit 202, and may be calculated by actually performing the encoding process.

  In step S3032, the data amount of the JPEG encoded data calculated in step S3031 is compared with the data amount of the encoded data generated by the first encoding unit 201 in step S202.

  In step S3033, based on the comparison result in step S3032, it is determined which of LS compression and JPEG compression is the optimal compression method. In general, it is determined that the data with a small amount of data is the optimum compression method.

  If it is determined in step S303 that LS compression has been performed, the quantization step is updated by shifting (ie, decreasing) the quantization step by a predetermined amount (S306), and the parameter control process is terminated. On the other hand, if it is determined that the compression is JPEG, the quantization step is not changed (S304) (when Th1 = Th2).

  If it is determined that the compression is JPEG and Th1 ≠ Th2, the following control may be performed. If the compression rate does not exceed the threshold (Th1) when the quantization step is shifted to the high compression side by a predetermined amount, the quantization step is shifted to the high compression side by a predetermined amount (that is, increased), and parameter control processing is performed. finish. On the other hand, if the compression rate exceeds the threshold (Th1) when the quantization step is shifted to the high compression side by a predetermined amount, the quantization step is not changed.

  Through the operations described above, the entire image data input in step S201 can be processed by sequentially processing a plurality of tile image data.

<Specific example of operation>
FIG. 5 is a diagram illustrating transition states of parameters (quantization steps) of the encoding processing unit according to the first embodiment. The horizontal axis direction represents 16 pieces of continuous tile image data that are sequentially processed, and the vertical axis direction represents the value of the quantization step set in the second encoding unit 202. Note that the upper parameter is a parameter indicating a low compression rate, and the lower parameter is a parameter indicating a high compression rate. Hereinafter, the tile image data on the left side are referred to as the first tile image data to the 16th tile image data in order from the left tile image data. The three threshold values are specified as Th0 <Th2 <Th1.

  Moreover, the selection result in step S301 is shown in the upper part of FIG. Specifically, “L” is written for LS compression, and “J” is written for JPEG compression. Furthermore, the determination result in step 303 is shown in the lower part of FIG. Specifically, “L” is written for LS compression, and “I” is written for JPEG compression.

  In addition, the “forced JPEG mode” in which JPEG compression is forcibly used is designated for the fifth to tenth and fifteenth tile images.

  For example, at point 501 which is a quantization step with the second tile image data, LS compression is selected in step S301. Therefore, the quantization step set in the second encoding unit 202 ends without being changed. As a result, the currently designated quantization step indicating low compression is maintained, and even when JPEG compression is selected for the subsequent (third) tile image data, the difference in image quality is less noticeable.

  At point 502, which is the quantization step for the fourth tile image data, JPEG compression is selected in step S301, but not the “forced JPEG mode”, and JPEG compression is selected in step S303. Therefore, the quantization step set in the second encoding unit 202 is shifted to the high compression side by a predetermined amount and updated. However, since the threshold Th2 is exceeded by shifting to the high compression side and updating, the “forced JPEG mode” is also specified. As a result, the LS compression is not selected for the subsequent (fifth) tile image data, and it is possible to prevent the high-compressed JPEG compressed image and the LS compressed image from being adjacent to each other. In addition, the amount of data can be reduced.

  At point 503, which is the quantization step for the seventh tile image data, JPEG compression is selected in the “forced JPEG mode”, and JPEG compression is also selected in step S303. However, since the compression ratio exceeds the threshold Th1 when the quantization step is shifted to the high compression side by a predetermined amount, the quantization step is not changed. As a result, image deterioration due to excessive JPEG compression can be prevented.

  At point 504, which is the quantization step for the eighth tile image data, JPEG compression is selected in the “forced JPEG mode”, and LS compression is selected in step S303. Therefore, the quantization step set in the second encoding unit 202 is shifted and updated by a predetermined amount toward the low compression side. On the other hand, at point 505, which is the quantization step for the 14th tile image data, JPEG compression is selected in step S301, but “forced JPEG mode” is not selected, and LS compression is selected in step S303. Therefore, the quantization step set in the second encoding unit 202 is shifted and updated by a predetermined amount toward the low compression side.

  In the above description, processing of continuous image tile image data included mainly in the same line image data has been described, and only initialization of parameters has been described for processing of different line image data. However, the tile image data of the line image included in the previously processed line image data and adjacent to the target tile may be considered as the adjacent tile image data of the target image tile image data. In this case, for example, the RAM 104 may be configured to store and refer to a history of encoding results corresponding to tile image data for at least one line.

  As described above, according to the first embodiment, when compression is performed by switching between LS compression and JPEG compression for each tile image data, it is possible to avoid adjacent tile images having greatly different image quality. As a result, it is possible to obtain more suitable compressed image data in which visual image quality deterioration is not noticeable.

(Second Embodiment)
In the second embodiment, a process when a periodic pattern image is included in the image data to be encoded will be described. In particular, a method for controlling to maintain a low compression rate for tile image data including a pattern image will be described. The apparatus configuration is the same as that of the first embodiment except that only a part of the internal program of the application 107 is changed.

  Image data in which a semi-transparent object is superimposed on a natural image is often used in the background of a presentation material creation application. Often, a translucent object expresses translucency by microscopically using a checkered mask to show through a background image.

  FIG. 8 is a diagram illustrating a translucent object. FIG. 8A is a view exemplarily showing a checkered mask having a transmittance of 50%. In the case of different transmittances, a semi-transparent object is realized with different thinning methods. FIG. 8B is a diagram exemplarily showing an image including a translucent object. That is, when a pattern image such as a checkered mask is compressed by irreversible compression such as JPEG, the decoded image is an image in which “blurring” or “bleeding” occurs. As a result, the boundary line between the tile image compressed with LS and the tile image compressed with JPEG becomes very conspicuous.

  In particular, LS compression is easy to select for pattern images, and JPEG compression is easy to select for natural images. As a result, for translucent objects, either LS compression or JPEG compression can be selected and can be switched frequently.

<Operation of the device>
FIG. 6 is a flowchart of parameter control processing according to the second embodiment. Below, only a different part from 1st Embodiment is demonstrated.

  If it is determined in step S302 that the mode is not “forced JPEG mode”, the type of image is determined in step S401. Here, two types of images are assumed: an image including a translucent pattern (Pattern) and a natural image not including a translucent pattern (Image). Specifically, the determination is performed by comparing the data amount of the encoded data output from the first encoding unit 201 with a preset threshold data amount (ThD) (image type determination unit). Then, when the data amount of the encoded data output by the first encoding unit 201 is larger than the threshold data amount, it is determined as a natural image (Image), and when it is equal to or smaller than the threshold data amount, it is determined as a semi-transparent pattern (Pattern). That is, here, the tile image data including the translucent pattern focuses on the property that the data amount of the encoded data by the LS compression is smaller (the compression ratio is higher) than the tile image data of the natural image. .

  If it is determined in step S401 that the pattern is a translucent pattern (Pattern), the shift amount (predetermined amount) of the quantization step is set smaller than the present (S402), and the quantization step is shifted to the high compression side by a predetermined amount. (S305), the parameter control process is terminated. On the other hand, if it is determined that the image is a natural image (Image), the quantization step is shifted by a predetermined amount to the high compression side (S305), and the parameter control process is terminated. That is, the JPEG compression quantization step allowed in the image area of the translucent pattern is limited to extremely low compression parameters. Therefore, control is performed so that the quantization step is shifted to high compression at a level not exceeding this compression rate. Or it is necessary to control so that it does not shift to the high compression side any more.

  If it is determined in step S303 that the compression is JPEG, the type of image is determined in step S402. If it is determined in step S402 that the pattern is a translucent pattern (Pattern), it is shifted by a predetermined amount toward the low compression side (S306), and the parameter control process is terminated. On the other hand, if it is determined that the image is a natural image (Image), the quantization step is not changed (S304).

<Specific example of operation>
FIG. 7A is a diagram illustrating a transition state of parameters (quantization steps) of the encoding processing unit according to the second embodiment. In the lower part of FIG. 7A, “L” is written for LS compression, “I” is written for JPEG compression (natural image), and “P” is written for JPEG compression (translucent pattern). The threshold Th2 ′ is as follows.
Th2 ′: The compression rate in JPEG compression (semi-transparent pattern) where the tile image boundary is not noticeable even when adjacent to the LS compressed image.

  For example, at point 701 which is the quantization step with the fifth tile image data, JPEG compression is selected in the “forced JPEG mode”, and it is determined that JPEG compression (natural image) is performed in step S402. Since the compression rate does not exceed the threshold (Th1) when the quantization step is shifted to the high compression side by a predetermined amount, the quantization step is shifted to the high compression side by a predetermined amount.

  At point 702, which is the quantization step for the eighth tile image data, JPEG compression is selected in the “forced JPEG mode”, and it is determined that JPEG compression (semi-transparent pattern) is performed in step S402. Therefore, the quantization step is shifted by a predetermined amount toward the low compression side.

  At point 703, which is the quantization step for the 13th tile image data, JPEG compression is selected in step S301, but it is not “forced JPEG mode”, and JPEG compression (translucent pattern) is determined in step S402. ing. Therefore, the shift amount (predetermined amount) of the quantization step is corrected to a smaller shift amount (corrected predetermined amount), and the quantization step is shifted to the high compression side by the corrected shift amount.

  As described above, according to the second embodiment, it is possible to obtain more suitable compressed image data in the image region of the translucent pattern.

(Modification)
In the second embodiment, the threshold Th1 may be controlled. In the following, an example of controlling the maximum compression rate (Th1) during JPEG compression using image attribute prediction will be described. Since processing other than prediction is the same as in the second embodiment, description thereof is omitted.

<Specific example of operation>
FIG.7 (b) is a figure which shows the transition state of the parameter (quantization step) of the encoding process part which concerns on a modification. The prediction result of the image attribute is described at the bottom of FIG.

  The image data sent from the data input unit 102 includes data representing attributes in the image in addition to the image data itself. The attribute information is, for example, a map created so that areas such as a character part, a graphic part, and an image part can be distinguished.

  Therefore, the parameter control unit 204 refers to the attribute information and confirms whether the tile image data currently being processed is an image portion or a graphic portion. In the case of the graphic portion, since it is known that LS compression is easily selected, the threshold value Th1 is shifted to low compression. As a result, the quantization step remains at low compression, so the time required to return to LS compression is shortened, and a higher quality image can be obtained.

  On the other hand, if it can be predicted that the image portion will continue, the threshold Th1 is shifted to high compression. Thereby, the compression rate at the time of JPEG compression can be earned, and the data amount of the encoded data with respect to the entire image data can be reduced.

(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 (6)

An image processing apparatus for compressing and encoding image data,
Input means for inputting image data in units of tile image data which is a pixel block of a predetermined size;
First encoding means for losslessly encoding input tile image data and generating lossless encoded data;
A second process of generating lossy encoded data by irreversibly encoding input tile image data by interposing a quantization process according to a quantization step equal to or lower than a first threshold corresponding to a predetermined maximum compression rate. Encoding means;
The lossless encoded data generated by the first encoding unit for the target tile image data is compared with the lossy encoded data generated by the second encoding unit for the target tile image data. First determination means for determining whether the amount of data is small;
Said lossless encoded data and the non-reversible encoding any selected selection means you outputs one as encoded data of the tile of interest image data with the data,
Updating means for updating the quantization step in preparation for encoding of the subsequent tile image data each time the encoded data of the tile image data of interest is selected and output;
If the quantization step set when irreversibly encoding the target tile image data is equal to or smaller than a second threshold corresponding to a compression rate smaller than the predetermined maximum compression rate, the target tile image data is included in the target tile image data. For subsequent tile image data, control is performed so as to select and output the encoded data that the first determination unit determines that the data amount is small according to the determination result of the first determination unit, and the tile image data of interest If the quantization step set when irreversibly encoding is larger than the second threshold value, the tile image data following the tile image data of interest is forcibly applied to the second encoding. and control means for controlling the pre-hexene-option means to select the lossy encoded data generated output by means,
An image processing apparatus comprising: The lossy encoded data generated when the tile image data is irreversibly encoded by the second encoding unit based on a predetermined initial quantization step, and the tile image data generated by the first encoding unit A second determination means for comparing the lossless encoded data and determining which data amount is small;
The updating means includes
When the selection unit selects and outputs the lossy encoded data according to the determination result of the first determination unit, the quantization step is increased by a predetermined amount,
When the selection means forcibly selects the lossy encoded data under the control of the control means, and the second determination means determines that the data amount of the lossy encoded data is small, the quantum Without changing the conversion step,
When the selection means forcibly selects the lossy encoded data under the control of the control means, and the second determination means determines that the data amount of the lossless encoded data is small, the quantization Reducing the step by the predetermined amount;
The image processing apparatus according to claim 1, wherein the quantization step is updated as described above. The update means forcibly selects the lossy encoded data by the selection means under the control of the control means, and the second determination means determines that the amount of the lossy encoded data is small In some cases, further
If the quantization step set when the target tile image data is lossy encoded is less than the first threshold when increased by the predetermined amount, the quantization step is increased by a predetermined amount. Let
When the quantization step set when the target tile image data is irreversibly encoded becomes larger than the first threshold when increased by the predetermined amount, the quantization step is not changed. The image processing apparatus according to claim 2, wherein the image processing apparatus is updated. When the data amount of the lossless encoded data generated by the first encoding unit for the target tile image data is equal to or less than a predetermined threshold data amount, the target tile image data is determined to be an image including a pattern image. Further comprising image type determination means for
The updating means includes
The selection unit selects and outputs the lossy encoded data according to the determination result of the first determination unit, and the image type determination unit determines that the tile image data of interest is an image including a pattern image. when, after the predetermined amount was changed to the predetermined amount is smaller than modifying the predetermined amount, the quantization step is increased by the corrected predetermined amount,
The selection means forcibly selects the lossy encoded data under the control of the control means, the second determination means determines that the amount of the lossy encoded data is small, and the image When the type determining unit determines that the tile image data of interest is an image including a pattern image, the quantization step is decreased by the predetermined amount.
The image processing apparatus according to claim 2. The first encoding means generates the lossless encoded data by JPEG-LS encoding,
The image processing apparatus according to claim 1, wherein the second encoding unit generates the lossy encoded data by JPEG encoding. A control method of an image processing apparatus for compressing and encoding image data,
An input step of inputting image data in units of tile image data which is a pixel block of a predetermined size;
A first encoding step of reversibly encoding input tile image data to generate lossless encoded data;
A second process of generating lossy encoded data by irreversibly encoding input tile image data by interposing a quantization process according to a quantization step equal to or lower than a first threshold corresponding to a predetermined maximum compression rate. Encoding process;
The lossless encoded data generated in the first encoding step for the target tile image data is compared with the lossy encoded data generated in the second encoding step for the target tile image data. A first determination step for determining whether or not the amount of data is small;
Said lossless encoded data and the lossy encoded data and either the focused tile image data in the selected you output selection step as encoded data,
An update step of updating the quantization step in preparation for encoding of the subsequent tile image data each time the encoded data of the tile image data of interest is selected and output;
If the quantization step set when irreversibly encoding the target tile image data is equal to or smaller than a second threshold corresponding to a compression rate smaller than the predetermined maximum compression rate, the target tile image data is included in the target tile image data. The subsequent tile image data is controlled so as to select and output encoded data determined to have a small amount of data in the first determination step according to the determination result of the first determination step, and the tile image of interest If the quantization step set when the data is lossy encoded is larger than the second threshold, the tile code data following the tile image data of interest is forcibly set to the second code. and a control step of controlling the pre-hexene-option process to output select lossy encoded data generated by the step,
Method of controlling an image processing apparatus which comprises a.