JP5197863B2 - Image processing device - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing method.

  Conventionally, a computer sends original data (text, graphics, table data, etc.) and copy-forgery-inhibited pattern data to a printer, and after the two data are combined by the printer, the combined image data (original data with a copy-forgery-inhibited pattern) obtained by combining is normally used. There is a technology to create originals by printing on paper.

  Here, the background pattern will be briefly described. The copy-forgery-inhibited pattern expresses information such as a character string in a state that is difficult for human eyes to see (in a hidden state), and is composed of a “remaining” region and a “disappearing” region. The “remaining” area is an area where relatively large dots (eg, black pixel group) are arranged, and the “disappearing” area is an area where relatively small dots (eg, black isolated pixels) are arranged. It is. “Remaining” means that the image in the original is reproduced on the copy. Further, “disappear” means that the image in the original is not reproduced on the copy (the density becomes low or disappears completely). The reflection density per certain area of the “remaining” region and the “disappearing” region is substantially the same on the original. For this reason, in the original state, it is not known that a character string or the like is expressed to the human eye. However, when the original is copied, the character string or the like embedded in the copied material will appear. Therefore, the background pattern is sometimes called a copy check background pattern. The reflection density is measured with a reflection densitometer.

  Since such a copy-forgery-inhibited document data tends to increase in data size, the data size is generally reduced by JPEG compression in order to reduce the processing load on the printer. For example, Patent Document 1 discloses a technique for efficiently JPEG compressing document data with a tint block.

JP 2008-028485 A

  However, when JPEG compression is performed on composite image data such as original data with a tint block, the high-frequency component data is deleted, and the black pixel portion constituting the tint block may become a gray pixel group. It was. Furthermore, by binarization, a black pixel group (medium size dot) is hit in the area where black isolated pixels (small dots) should be hit, or nothing is hit on the contrary. A phenomenon may occur, and the tint block data included in the composite image data may be corrupted. As a result, there has been a problem that even if the original obtained by printing the document data with the tint block is copied, the character string or the like that should appear on the copy does not appear.

  Further, the above-described problems can occur not only with document data with a background pattern. That is, this also occurs in composite image data including an image such as a two-dimensional code such as a QR code, a glyph code (registered trademark) that is a dot-type barcode, and an LVBC (Low Visibility BarCode) used for digital watermarking. Was expected.

  In order to solve the above problems, an image processing apparatus of the present invention comprises the following arrangement.

A determination unit for determining whether the acquired image data is image data having a resolution equal to or higher than a predetermined resolution or image data having a resolution lower than the predetermined resolution; When it is determined that the acquired image data is image data having a resolution equal to or higher than the predetermined resolution, the acquired image data is sent to a halftone processing unit, and the acquired image data by the determination unit Is determined to be image data having a resolution less than the predetermined resolution, the acquired image data is sent to the compression processing means, and halftone processing is performed on the sent image data. Te, and the halftone processing means for sending image data that has been halftoned storage means, the lossy encoding method on the image data sent That compresses the go, to the said compression processing means for sending compressed image data in the storage means, the storage means for storing the image data transmitted, characterized in that it has a.

  According to the present invention, when printing or the like, composite image data including image data such as a tint block is converted to an optimal image data size without causing image quality deterioration that may damage the image data such as the tint block. It can be stored (spooled) in an HDD or the like.

1 is a diagram illustrating an overall configuration of an image processing system including an image processing apparatus according to a first embodiment. 2 is a diagram illustrating an internal configuration of an image processing apparatus 102. FIG. 4 is a functional block diagram illustrating details of an image data encoding unit and an image data decoding unit according to the first embodiment. FIG. 3 is a flowchart illustrating a flow of processing from image processing of image data to be printed received from a computer according to the first embodiment by an image processing apparatus to printing of the processed image data by a printer. It is a functional block diagram which shows the detail of the image data encoding part which concerns on Embodiment 2, and an image data decoding part. 10 is a flowchart showing a flow of processing until image data to be printed received from a computer 101 is image-processed by an image processing apparatus 102 and processed image data is printed by a printer 103 according to the second embodiment.

[Embodiment 1]
Hereinafter, a preferred embodiment of the present invention will be described by taking as an example the case of printing composite image data including copy-forgery-inhibited pattern data. As a matter of course, the present invention can also be applied to composite image data including image data such as the above-described QR code, glyph code, and LVBC, and is not limited to the case of a background pattern. That is, composite image data including image data that directly or indirectly represents certain information composed of character strings, numerical values, etc., depending on the combination and arrangement of pixels having an ON value (information) and pixels having an OFF value (information) If so, it is applicable to all of them.

  In the case of a tint block, pixels having an ON value are black pixels for monochrome printing, and cyan pixels, magenta pixels, yellow pixels, and black pixels for color printing with CMYK color materials. A pixel having an OFF value is a white pixel in both monochrome and color printing. A background pattern is formed by arranging dots composed of pixels other than white pixels on a background composed of white pixels. Therefore, in general, the ground pattern includes a ground pattern composed of cyan and white pixels, a ground pattern composed of magenta pixels and white pixels, a ground pattern composed of yellow pixels and white pixels, black pixels and white pixels. There are a total of four types of background patterns composed of Incidentally, in RGB, black is represented by numerical values such as (R, G, B) = (0, 0, 0) and white is represented by (R, G, B) = (255, 255, 255). Therefore, for example, copy-forgery-inhibited pattern data in black and white printing includes black (0, 0, 0) pixels as pixels having an ON value and white (255, 255, 255) pixels as pixels having an OFF value. The data is a combination.

  FIG. 1 is a diagram illustrating an overall configuration of an image processing system including an image processing apparatus according to the first embodiment. Reference numeral 101 denotes a computer (PC), reference numeral 102 denotes an image processing apparatus, and reference numeral 103 denotes an image output apparatus (printer) that outputs (prints) image data. The computer 101, the image processing apparatus 102, and the printer 103 are connected via a network 104. Image data (PDL data) to be printed is transmitted from the computer 101 to the image processing apparatus 102, and image data (bitmap data) subjected to predetermined image processing by interpreting the PDL command is printed by the printer 103. . In this embodiment, a case where image data to be printed (image data sent from the computer 101) is composed of copy-forgery-inhibited pattern data and document data is referred to as “copy-forgery-inhibited pattern printing”, and is composed of only document data. Is called “normal printing”.

  Image data attribute information indicating the attribute of the image data is added to the image data to be printed as header information of the image data. For example, in the case of copy-forgery-inhibited pattern data, image data attribute information indicating that the copy-forgery-inhibited pattern data is added as header information of the image data. If the image data is document data, the image data attribute information indicating that the image data is the document data is also sent as header information of the image data. The image data attribute information is referred to by the image processing apparatus 102 before the image processing is executed in order to perform appropriate processing on the image data in the image processing apparatus 102.

  In this figure, the image processing apparatus 102 and the printer 103 are illustrated as separate apparatuses, but they may be configured as a single apparatus.

  FIG. 2 is a diagram illustrating an internal configuration of the image processing apparatus 102.

  A rendering unit 201 interprets the PDL description image data sent from the computer 101, and performs processing for imaging (bitmap) information about the object or figure given as numerical data. In the case of copy-forgery-inhibited pattern printing, when the image data is composed of document data and copy-forgery-inhibited pattern data, processing is also performed in which both data are combined to form copy-forgery-inhibited document data (composite image data). At this time, image data attribute information indicating that the copy-forgery-inhibited pattern data is included is added to the generated composite image data as header information of the composite image data.

  An image data input unit 202 receives rendered image data from the rendering unit 201 and sends the received image data to the image data encoding unit 203 as necessary.

  An image data encoding unit 203 encodes (compresses) the image data received from the image data input unit 202. Details of the processing of the image data encoding unit 203 will be described later.

  An image data storage unit 204 includes an HDD or the like.

  An image data decoding unit 205 decodes (decompresses) the image data encoded by the image data encoding unit 203. Details of the processing of the image data decoding unit 205 will be described later.

  An image data output unit 206 outputs the decoded image data received from the image data decoding unit 205 to the printer 103.

  In the case of “background pattern printing”, it has been described that both the background pattern data, which is image data to be printed, and the document data are provided from the computer 101. However, an aspect of receiving only the document data from the computer 101 and printing the background pattern is excluded. Not what you want. It is also possible to perform tint block printing by a method of generating tint block data in the image processing apparatus 102 and synthesizing it with original data received from the computer 101. In that case, as shown by a broken line in FIG. 2, a tint block data generation unit 207 and a synthesis unit 208 are provided in the image processing apparatus 102. Therefore, in the present embodiment in which both original data and ground pattern data are sent to the image processing apparatus 102 as copy-forgery-inhibited pattern image data, the ground pattern data generation unit 207 and the composition unit 208 are not used.

  Next, details of processing in the image processing apparatus 102 according to the present embodiment will be specifically described with reference to FIGS. 3 and 4.

  3A and 3B are functional block diagrams illustrating details of the image data encoding unit 203 and the image data decoding unit 205, respectively. First, the image data encoding unit 203 will be described with reference to FIG.

  The image data determination unit 301 determines whether or not the copy-forgery-inhibited pattern data is included in the image data received from the computer 101. Whether the image data includes the copy-forgery-inhibited pattern data is determined by referring to image data attribute information added as header information to the image data. The determination may be performed by image recognition instead of referring to the image data attribute information.

  The first gamma correction unit 302 performs gamma correction processing according to the characteristics of the printer 103. The γ value used in the gamma correction process is determined by actually performing test printing with the printer 103 and measuring the density of image data obtained by scanning the printed matter.

  The first halftone processing unit 303 performs halftone processing (halftone processing) for expressing a halftone using only black and white colors.

  The second image data encoding unit 304 performs compression processing by lossless encoding on the halftone (binarized) image data.

  The compression buffer 305 is a memory unit for temporarily storing image data.

  The encoding quantization matrix selection unit 306 holds a plurality of quantization tables (quantization matrices) having different compression ratios (quantization scales), and in order from a quantization matrix having a lower compression ratio in place of a smaller image quality deterioration. The data is output to the first image data encoding unit 307. Each numerical value constituting the quantization matrix is set to a predetermined value in advance.

  The first image data encoding unit 307 performs compression processing by irreversible encoding (JPEG) on image data that does not include copy-forgery-inhibited pattern data. That is, discrete cosine transform (DCT) is performed on the image data, and quantization processing is performed using the quantization matrix sequentially output from the encoding quantization matrix selection unit 306. On the other hand, the encoding process is performed. This process is repeated until the image data fits in a predetermined memory capacity, and information on the finally selected quantization matrix is added to the image data attribute information.

  Next, the image data decoding unit 205 will be described with reference to FIG.

  The encoding determination unit 311 determines whether the encoded image data is reversibly compressed image data (that is, including copy-forgery-inhibited pattern data) or irreversibly compressed image data (not including copy-forgery-inhibited pattern data). ) Is performed.

  The second image data decoding unit 312 performs a process for decoding the losslessly compressed image data.

  The decoding inverse quantization matrix unit 313 holds an inverse quantization table (inverse quantization matrix), and an inverse quantum corresponding to the quantization matrix used in the quantization processing in the first image data encoding unit 307. The quantization matrix is output to the first image data decoding unit 314.

  The first image data decoding unit 314 performs processing for decoding image data that has been subjected to lossy encoding compression. That is, JPEG-compressed image data is decompressed (decompressed), inverse-quantized using the inverse quantization matrix output from the decoded inverse quantization matrix selection unit 313, and the obtained inverse-quantized data is subjected to inverse discrete cosine. Processing for conversion (IDCT) is performed.

  The expansion buffer 315 is a memory unit for temporarily storing image data, like the compression buffer 305.

  Similar to the first gamma correction unit 302, the second gamma correction unit 316 performs gamma correction processing according to the characteristics of the printer 103.

  Similar to the first halftone processing unit 303, the second halftone processing unit 317 performs halftone processing (halftone processing) for expressing a halftone using only black and white colors.

  A scaling unit 318 enlarges / reduces image data that has been subjected to gamma correction processing and halftoning processing after decoding and does not include copy-forgery-inhibited pattern data at a predetermined scaling factor using a known technique such as a bilinear method. Process.

  The rotator 319 performs a process of rotating the image data that does not include the copy-forgery-inhibited pattern data by a predetermined angle after the decoding and the gamma correction process and the halftone process.

  The image data encoding unit 203 and the image data decoding unit 205 configured as described above have the following features.

  First, the first gamma correction unit 302/316 is placed in front of the first halftone processing unit 303/317. If the image data becomes binary (or substantially binary) due to halftoning, gamma correction based on continuous tone cannot be performed thereafter, and the image printed by the printer 103 The problem arises that the image is altered from the original image. Therefore, the first gamma correction unit 302 / second gamma correction unit 316 are arranged in front of the first halftone processing unit 303 / second halftone processing unit 317 in order to perform gamma correction before halftoning. Yes.

  Next, image data that does not include copy-forgery-inhibited pattern data is irreversibly compressed (JPEG compression) by the first image data encoding unit 307, and can be enlarged / reduced at any magnification by the scaling unit 318 after decoding. It has a simple structure. In the first place, image data that has been binarized by halftoning has a significant deterioration in image quality depending on the scaling factor, and the scaling process is substantially limited. In view of this, image data that does not include copy-forgery-inhibited pattern data is subjected to JPEG compression instead of halftone processing, and image data that has been halftoned after decoding can be enlarged or reduced by a scaling unit 318.

  Furthermore, image data that does not include copy-forgery-inhibited pattern data has a configuration in which an image can be rotated at an arbitrary angle by a rotation unit 319 after decoding. In the first place, image data that has been binarized by halftoning may change the pixel density by rotating depending on the characteristics of the printer 103. That is, the printer has a characteristic that it is strong in the main scanning direction (can be printed accurately even with a pixel group having a small number of continuous pixels in the main scanning direction) but weak in the sub-scanning direction. There may be a problem that the expressed density becomes thin. Therefore, image data that does not include copy-forgery-inhibited pattern data is subjected to JPEG compression instead of halftone processing, so that rotation processing by the rotation unit 319 can be performed on image data that has been halftoned after decoding.

  In the case of printing by a method in which a user gives a print instruction to image data stored in the HDD 204, the designated image data is sent from the HDD 204 to the image data decoding unit 205, and a predetermined decoding process is performed. Then, it is printed by the printer 103.

  By configuring the image data encoding unit 203 and the image data decoding unit 205 as described above, the image processing apparatus according to the present invention allows the image data to be printed to be image data including copy-forgery-inhibited pattern data. Is halftoned and spooled without JPEG compression. As a result, the data size of the image data can be reduced while preventing a situation in which the tint block data is damaged or deteriorated by JPEG compression.

  FIG. 4 shows a flow of processing until image data to be printed received from the computer 101 is processed by the image processing apparatus 102 and the processed image data is printed by the printer 103 according to the present embodiment. It is a flowchart.

  First, in step 400, the image processing apparatus 102 acquires image data to be printed from the computer 101. Hereinafter, in this step, it is assumed that the image data including the document data and the copy-forgery-inhibited pattern data is acquired from the computer 101 (that is, the document data and the copy-forgery-inhibited pattern data are continuously transmitted from the computer 101). An explanation shall be added. Composite image data rendered by the rendering unit 201 is generated based on the acquired image data, and the generated composite image data is sent to the image data encoding unit 203 via the image data input unit 202. Note that, as described above, image data attribute information indicating that the copy-forgery-inhibited pattern data is included is added to the composite image data as header information.

  In step 401, the image data determination unit 301 of the image data encoding unit 203 determines whether or not the copy-forgery-inhibited pattern data is included in the image data. If it is determined that the copy-forgery-inhibited pattern data is included, the image data is sent to the first gamma correction unit 302. On the other hand, if it is determined that the copy-forgery-inhibited pattern data is not included, the image data is sent to the compression buffer 305. Here, it is determined that the copy-forgery-inhibited pattern data is included, and is sent to the first gamma correction unit 302.

  In step 402, the first gamma correction unit 302 performs gamma correction on image data (synthesized image data) including copy-forgery-inhibited pattern data. The gamma corrected composite image data is sent to the first halftone processing unit 303.

  In step 403, the first halftone processing unit 303 performs halftone processing on the gamma-corrected composite image data. The halftone composite image data is sent to the second image data encoding unit 304.

  In step 404, the second image data encoding unit 304 performs a compression process using a lossless encoding method on the halftone composite image data.

  On the other hand, if it is determined in step 401 that the copy-forgery-inhibited pattern data is not included, in step 405, the first image data encoding unit 307 performs irreversible encoding (JPEG) on the image data (original data only). Perform compression processing.

  It should be noted that when encoding is performed in steps 404 and 405, information indicating the encoding (compression) method used is added to the image data attribute information.

  In step 406, the image processing apparatus 102 stores the encoded image data in the HDD 204 as a data storage unit. In the present embodiment in which printing is performed by the printer 103 upon completion of image processing upon receiving a print instruction from the computer 101, this “storage” can be read as “spool”. Here, the composite image data is compressed and stored by the lossless encoding method, but image data attribute information indicating that the copy-forgery-inhibited pattern data is included and compressed by the lossless encoding method is added. In this state, it is stored in the HDD 204.

  As described above, when the image data to be printed includes copy-forgery-inhibited pattern data, halftone processing is performed instead of JPEG compression, and the halftoned image data is stored in the HDD 204. As a result, the data size of the image data is reduced while suppressing deterioration or damage of the image of the copy-forgery-inhibited pattern data. On the other hand, when the image data to be printed does not include copy-forgery-inhibited pattern data, the image data whose data size is suppressed by JPEG compression is stored in the HDD 204.

  In step 407, the image processing apparatus 102 sends the image data stored (spooled) in the HDD 204 to the encoding determination unit 311. The encoding determination unit 311 refers to the image data attribute information and includes image data including copy-forgery-inhibited pattern data. Determine whether or not. If it is determined that the copy-forgery-inhibited pattern data is included, the encoding determination unit 311 sends the image data to the second image data decoding unit 312 (to step 408). If it is determined that the copy-forgery-inhibited pattern data is not included, the encoding determination unit 311 sends the image data to the first image data decoding unit 314 (to step 409). In the case of composite image data, it is determined that the copy-forgery-inhibited pattern data is included, and the process proceeds to step 408.

  In step 408, the second image data decoding unit 312 performs lossless decoding (development) on the composite image data including the copy-forgery-inhibited pattern data. The developed image data is output to the printer 103 via the image data output unit 206.

  On the other hand, in step 409, the first image data decoding unit 314 performs irreversible decoding (development) on the image data not including the copy-forgery-inhibited pattern data. The developed image data is sent to the second gamma correction unit 316.

  In step 410, the second gamma correction unit 316 performs gamma correction on the developed image data. The gamma-corrected image data is sent to the second halftone processing unit 317.

  In step 411, the second halftone processing unit 317 converts the gamma-corrected image data into a halftone. The halftoned image data is sent to the scaling unit 318 or the rotation unit 319 according to a user instruction.

  In step 412, the scaling unit 318 or the rotation unit 319 performs enlargement / reduction or rotation processing on the halftoned image data according to the content specified by the user. The image data that has undergone predetermined processing is sent to the printer 103 via the image data output unit 206.

  In step 413, the printer 103 prints out the developed image data. Since the developed image data in the case of copy-forgery-inhibited pattern printing is not JPEG compressed, damage to the copy-forgery-inhibited pattern data is suppressed, and the copy-forgery-inhibited pattern is reproduced on the printed matter without damaging dots due to pixels having ON values.

  As described above, according to the present embodiment, when the composite image data including the copy-forgery-inhibited pattern data is printed, the image data is encoded to an optimum image data size without causing image quality deterioration that may damage the copy-forgery-inhibited pattern data. It becomes possible to save in the HDD. In the case of normal printing, the data size of the image data is efficiently compressed by JPEG compression, so that a large amount of HDD can be prevented from being consumed.

[Embodiment 2]
In the first embodiment, when copy-forgery-inhibited pattern data is included in image data to be printed, halftoning is performed without JPEG compression. Next, even if the image data to be printed does not include copy-forgery-inhibited pattern data, when the resolution is higher than a predetermined resolution, a mode of halftoning without JPEG compression will be described as a second embodiment. .

  FIGS. 5A and 5B are functional block diagrams showing details of the image data encoding unit 203 ′ and the image data decoding unit 205 ′ according to the present embodiment, respectively. In addition, the same code | symbol is attached | subjected about the part which is common in the image data encoding part 203 and the image data decoding part 205 which concern on Embodiment 1, and the description is abbreviate | omitted.

  Reference numeral 501 denotes a resolution determination unit that acquires the resolution of image data that is determined not to include copy-forgery-inhibited pattern data by the image data determination unit 301 and determines whether the acquired resolution is equal to or higher than a predetermined resolution. . The resolution is acquired by referring to the header information (image data attribute information) of the image data. That is, in the case of this embodiment, resolution-related information is added as image data attribute information to image data to be printed sent from the computer 101.

  Reference numeral 311 ′ denotes an encoding determination unit, which determines whether the encoded image data includes copy-forgery-inhibited pattern data, similarly to the encoding determination unit 311 according to the first embodiment. In addition, it is also determined whether the image data is high-resolution image data. The determination regarding the resolution is also made by referring to the header information (image data attribute information) of the image data.

  Other units are the same as those of the image data encoding unit 203 and the image data decoding unit 205 according to the first embodiment.

  FIG. 6 shows a flow of processing until image data to be printed received from the computer 101 is processed by the image processing apparatus 102 and the processed image data is printed by the printer 103 according to the present embodiment. It is a flowchart. Note that the description of the parts common to the flowchart of FIG. 4 according to the first embodiment is simplified or omitted, and here, differences will be mainly described.

  In step 600, when the image processing apparatus 102 acquires the image data to be printed, in step 601, the image data determination unit 301 of the image data encoding unit 203 ′ determines whether the image data includes copy-forgery-inhibited pattern data. To do.

  If it is determined that the copy-forgery-inhibited pattern data is included, the process proceeds to step 602, and the image data compressed by the lossless encoding method through the gamma correction process and halftoning is stored in the HDD 204 (steps 602, 603, and 604). And 607). On the other hand, if it is determined that the copy-forgery-inhibited pattern data is not included, the process proceeds to step 605.

  In step 605, the resolution determination unit 501 acquires the resolution of the image data, and determines whether the acquired resolution is equal to or higher than a predetermined resolution. If the resolution is higher than the predetermined resolution, the process proceeds to step 602. If the resolution is lower than the predetermined resolution, the process proceeds to step 606.

  Here, it is assumed that image data that does not include copy-forgery-inhibited pattern data and has a resolution of 2400 dpi is acquired from the computer 101, and 1200 dpi is preset as the predetermined resolution. In this case, since the resolution of the image data to be printed is equal to or higher than the predetermined resolution, the process proceeds to step 602. The image data to be printed is subjected to gamma correction processing and halftoning processing without being JPEG compressed (steps 602 and 603) and spooled in the HDD 204 (step 607).

  If the resolution of the image data to be printed is 600 dpi, it is determined that the resolution is less than the predetermined resolution, the process proceeds to step 606, and after JPEG compression, it is spooled in the HDD 204 (step 607). .

  In step 608, the encoding determination unit 311 ′ determines whether the encoded image data includes copy-forgery-inhibited pattern data, or whether the image data has a predetermined resolution or higher. If the copy-forgery-inhibited pattern data is included or the resolution is higher than a predetermined resolution, a decompression process using a lossless decoding method is performed (step 609).

  On the other hand, if the copy-forgery-inhibited pattern data is not included or the resolution is less than the predetermined resolution, the process proceeds to step 610. Each process of step 610 to step 613 is the same as step 409 to step 412 of FIG.

  In step 614, the printer 103 prints out the developed image data. The developed image data in the case of copy-forgery-inhibited pattern printing or high-resolution image data printing is not JPEG-compressed, so that data corruption is suppressed and a high-quality image is reproduced on the printed matter.

  As described above, according to the present embodiment, not only composite image data including copy-forgery-inhibited pattern data but also high-resolution image data having a predetermined resolution or higher is encoded with an optimal image data size without deterioration in image quality. And can be stored in the HDD.

(Other embodiments)
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.

101 Computer 102 Image Processing Device 103 Printer

Claims (17)

Determining means for determining whether the acquired image data is image data having a resolution equal to or higher than a predetermined resolution or image data having a resolution lower than the predetermined resolution;
If it is determined by the determination means that the acquired image data is image data having a resolution equal to or higher than the predetermined resolution, the acquired image data is sent to a halftone processing means, and the determination means acquires the acquisition Means for sending the acquired image data to the compression processing means when it is determined that the obtained image data is image data having a resolution lower than the predetermined resolution;
The halftone processing means for performing halftone processing on the sent image data and sending the halftone processed image data to the storage means ;
The compression processing means for performing compression processing by the lossy encoding method on the sent image data, and sending the compressed image data to the storage means ;
The storage means for storing the transmitted image data;
An image forming apparatus comprising:   2. The image processing apparatus according to claim 1, wherein the image data subjected to halftone processing by the halftone processing unit is subjected to compression processing by a lossless encoding method before being stored in the storage unit. 2. The image forming apparatus according to claim 1, wherein gamma correction processing is performed before halftone processing in the halftone processing means. A first decompressing unit that decompresses the image data when the image data read from the storage unit is image data that has been compressed by the lossy encoding method in the compression processing unit;
A second expansion means for expanding the image data when the image data read from the storage means is image data that has been compressed by the lossless encoding method;
The image forming apparatus according to claim 2, further comprising: The image forming apparatus according to claim 4, wherein halftone processing is performed on the image data developed by the first development unit. 6. The image forming apparatus according to claim 5, wherein a gamma correction process is performed before the halftone process is performed on the image data developed by the first development unit. 6. The scaling unit according to claim 5, further comprising a scaling unit that performs a process of enlarging or reducing the image data developed by the first developing unit subjected to the halftone process at a predetermined scaling factor. Image forming apparatus. The image forming apparatus according to claim 5, further comprising a rotating unit that performs a process of rotating the image data developed by the first developing unit that has undergone the halftone process at a predetermined angle. A determination step of determining whether the acquired image data is image data having a resolution equal to or higher than a predetermined resolution or image data having a resolution lower than the predetermined resolution;
When it is determined in the determination step that the acquired image data is image data having a resolution equal to or higher than the predetermined resolution, the acquired image data is sent to a halftone processing unit, and the acquisition is performed in the determination step. If it is determined that the obtained image data is image data having a resolution lower than the predetermined resolution, the acquired image data is sent to a compression processing means; and
A halftone processing step of performing halftone processing on the sent image data and sending the halftone processed image data to a storage means ;
A compression processing step of performing compression processing by the lossy encoding method on the sent image data, and sending the compressed image data to the storage unit ;
A storage step of storing the transmitted image data in the storage unit;
Image forming method, which comprises a. The image forming method according to claim 9, further comprising a step of performing compression processing by a lossless encoding method before storing the image data subjected to halftone processing in the halftone processing step in the storing step. . The image forming method according to claim 9, further comprising performing a gamma correction process before the halftone process in the halftone process step. A first expansion step of expanding the image data when the image data stored in the storage step is image data that has been subjected to compression processing by a lossy encoding method in the compression processing step;
A second expansion step of expanding the image data when the image data stored in the storage step is image data compressed by the lossless encoding method;
The image forming method according to claim 10, further comprising: The image forming method according to claim 12, further comprising a step of performing a halftone process on the image data developed in the first development step. The image forming method according to claim 13, further comprising a step of performing a gamma correction process before performing the halftone process on the image data developed in the first development step. 14. The image according to claim 13, further comprising a scaling step of performing a process of enlarging or reducing the image data developed in the first developing step subjected to the halftone process at a predetermined scaling factor. Forming method. The image forming method according to claim 13, further comprising a rotation step of performing a process of rotating the halftone processed image data expanded in the first expansion step at a predetermined angle. A program for causing a computer to execute the image forming method according to any one of claims 9 to 16.

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