JP5003394B2 - File generation program, image processing apparatus, and image processing method - Google Patents

Description

  The present invention relates to a file generation program, an image processing apparatus, and an image processing method for generating an image file in a multilayer data format.

  Conventionally, the original image data to be processed is separated into edge portion image data such as characters and line drawings and non-edge portion image data such as a picture, and a multi-layer data format including a layer of each image data A technique for generating an image file is known (see, for example, Patent Document 1).

  Further, Non-Patent Document 1 provides suitable image quality while greatly compressing the amount of data by applying an appropriate compression process according to the type of layer to each layer and then integrating the layers after compression. A technique for generating an image file in PDF format is disclosed.

Japanese Patent No. 3915931 Fumihiro Hasegawa and three others, “High Compression PDF Technology”, Ricoh Technical Report No. 30, December 2004, p93-97

  However, in an image file in a multi-layer data format, since the original image data is represented by being separated into a plurality of layers, handling of the content of the image data itself may be complicated. For example, when performing a character search on an image file in a multi-layer data format, it is necessary to perform a character search process using a pattern matching method on each image data of a plurality of layers. The amount of calculation increases and a lot of processing time is required. Further, even if a character search is performed on only the image data of the edge portion among a plurality of image data included in the image file, it is necessary to perform a pattern matching process on one image data. Will become longer. As described above, the conventional image file in the multi-layer data format has a problem in that the processing of characters is complicated and it becomes difficult to handle characters.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A file generation program for generating an image file representing an image by a plurality of layers from image data representing an image to be processed, the computer representing an image represented by the image data Layer separating means for separating into image layers, character layer generating means for extracting characters included in the image represented by the image data, and generating a character layer representing the extracted characters, the plurality of image layers and the characters A file generation program that functions as image file generation means for integrating the layers to generate the image file.

  According to this configuration, in addition to the plurality of image layers from which the image to be processed is separated, the character layer representing the characters included in the image to be processed is further integrated into the image file. An excellent multi-layer data format image file can be obtained. For example, when performing a character search process on this image file, it is possible to perform a character search with a simple process by referring to the character layer.

  Application Example 2 In the file generation program, the plurality of image layers separated by the layer separation unit include at least an image layer representing an edge portion in an image represented by the image data, and the character layer generation unit includes: A file generation program that extracts characters included in the image data based on an image layer representing the edge portion.

  According to this configuration, since the characters are extracted based on the edge portion of the image data, the character extraction accuracy is improved, and a character layer that accurately represents the characters included in the image data to be processed can be obtained.

  Application Example 3 In the file generation program, the character layer generation unit generates the character layer that represents the extracted characters in a text data format.

  According to this configuration, since the character layer is expressed in the text data format, it is possible to obtain an image file in a data format that is easy to handle for characters. According to this image file, it is possible to perform a character search by a simple process with reference to the text data of the character layer.

  Application Example 4 In the file generation program, the character layer generation unit generates the character layer representing the extracted character in a vector data format.

  According to this configuration, since the character layer is represented in the vector data format, an image file with excellent character quality can be obtained.

  [Application Example 5] In the file generation program, the character layer generation unit, when a plurality of characters having character attributes that differ only in character size are extracted, converts at least one of the plurality of characters into a vector data format. A file generation program for generating the character layer by describing a magnification of a character size with respect to a character represented by vector data for other characters.

  According to this configuration, in the character layer, at least one character is represented by vector data among a plurality of characters having character attributes that differ only in character size, and other characters are represented by a character size magnification. Therefore, the data amount of the character layer is reduced. Therefore, the data amount of the image file can be reduced.

  Application Example 6 In the file generation program, the file generation program further causes the computer to function as a compression unit that performs compression processing on each of the plurality of image layers.

  According to this configuration, since the compression process is performed for each of the plurality of image layers, the data amount of the image file can be reduced.

  Application Example 7 In the file generation program, the plurality of image layers separated by the layer separation unit include at least an image layer representing an edge portion in an image represented by the image data, and the compression unit includes the edge A file generation program that performs compression processing with higher edge reproducibility on an image layer representing a portion than compression processing on other image layers.

  According to this configuration, the edge portion of the image data is compressed with higher edge reproducibility than the other image layers. Therefore, each image layer is compressed and the amount of data is reduced, and the edge reproducibility is excellent. An image file with suitable image quality can be obtained.

  Application Example 8 In the file generation program, the compression unit performs a compression process for reducing the number of gradations for an image layer representing the edge portion of the plurality of image layers, and for the other image layers. Is a file generation program that performs compression processing to reduce resolution.

  According to this configuration, the image layer representing the edge portion after the compression processing has a higher resolution than the other image layers, so that an image file with a small amount of data and excellent edge reproducibility can be obtained. .

  Application Example 9 A layer separating unit that separates an image represented by image data to be processed into a plurality of image layers, a character layer representing the extracted character by extracting characters included in the image represented by the image data A character layer generating means for generating the image layer, and an image file generating means for generating an image file including the plurality of image layers and the character layer by integrating the plurality of image layers and the character layer. An image processing apparatus.

  According to this configuration, it is possible to obtain an image file in a multilayer data format that is easy to handle with respect to characters and excellent in usability.

  Application Example 10 Separating an image represented by image data to be processed into a plurality of image layers, extracting characters included in the image represented by the image data, and generating a character layer representing the extracted characters And a step of integrating the plurality of image layers and the character layer to generate an image file including the plurality of image layers and the character layer.

  In this way, it is possible to obtain an image file in a multi-layer data format that is easy to handle with respect to characters and is easy to use.

(First embodiment)
Hereinafter, a first example according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a hardware configuration of the image processing apparatus according to the first embodiment. Specifically, the image processing apparatus 1 is a general-purpose personal computer or the like. As shown in FIG. 1, the CPU 10, the ROM 20, the RAM 30, a hard disk (hereinafter referred to as “HD”) 40, and an input I / F 50. And a display I / F 60.

  The CPU 10 is a main control device of the image processing apparatus 1, and executes various processes such as a file generation process and a file browsing process described later in cooperation with the ROM 20 and the RAM 30 by executing a program recorded in the HD 40. The input I / F 50 is an interface portion with an external input device, and input devices such as a mouse 2 and a keyboard 3 are connected thereto. The display I / F 60 is an interface part with an external display device, and a display device such as the display 4 is connected thereto.

  The HD 40 stores a file generation program GP and a file browsing program RP in advance. The file generation program GP and the file browsing program RP are supplied to the image processing apparatus 1 in a form recorded on a recording medium and recorded on the HD 40. Examples of the recording medium include various computer-readable recording media such as a flexible disk, an optical disk such as a CD-ROM and a DVD-ROM, a magneto-optical disk, a memory card, and a portable hard disk. However, the image processing apparatus 1 may record the file generation program GP in the HD 40 by downloading the file generation program GP from the server through the telecommunication line.

  FIG. 2 shows a functional configuration of the image processing apparatus 1. The CPU 10 reads out and executes the file generation program GP from the HD 40, and as shown in FIG. 2, the layer separation unit (layer separation unit) 71, the layer compression unit (compression unit) 72, and the text layer generation unit ( A file generation application 70 having a character layer generation unit 73 and a layer integration unit (image file generation unit) 74 functions.

  The layer separation unit 71 performs processing for separating image data to be processed into a plurality of image layers. Although details will be described later, the layer separation unit 71 removes the bitmap image data from the first edge layer representing the edge portion included in the image data, the second edge layer representing the color information of the edge portion, and the edge portion. The image is separated into a total of three image layers including the non-edge layer including the portion.

  The layer compression unit 72 performs compression processing on each layer separated by the layer separation unit 71 by an appropriate method for each layer so as to realize a high compression rate while suppressing image quality deterioration.

  The text layer generation unit 73 performs character extraction processing on the first edge layer representing the edge portion, and generates a text layer (character layer) representing the extracted characters in the text data format.

  The layer integration unit 74 integrates the three image layers and the text layer after compression processing to generate a single image file, and performs processing for recording the generated image file on the HD 40.

  That is, the file generation application 70 has a function of generating an image file in a multilayer data format including the first edge layer, the second edge layer, the non-edge layer, and the text layer in a compressed data format from the image data to be processed. have.

  Further, the CPU 10 reads the file browsing program RP from the HD 40 and executes it, so that the file browsing application 80 having the display processing unit 81 and the search processing unit 82 functions.

  The display processing unit 81 performs display processing for restoring image data in a bitmap format from a plurality of image layers included in the image file and displaying the data on the display 4 or displaying each of the plurality of layers on the display 4.

  The search processing unit 82 refers to the text layer and performs character search processing on the image file.

  That is, the file browsing application 80 has a function of displaying an image of the image file generated by the file generation application 70 and a function of searching for characters included in the image file.

  Next, file generation processing performed by the file generation application 70 will be described in detail with reference to the flowchart of FIG.

  For example, the user operates the mouse 2 or the keyboard 3 to specify bitmap image data such as a scanner read image to be processed among the image data recorded on the HD 40, and generate an image file from the specified image data When the file generation application 70 is instructed to do so, the file generation process of FIG. 3 is started. When the file generation process is started, first, the CPU 10 reads the designated image data from the HD 40 to obtain the image data to be processed (step S100).

  Next, the CPU 10 performs processing for separating the image data to be processed into a plurality of layers (step S110). Here, as shown in FIG. 4 as an example, by performing edge detection processing using an edge detection filter such as Laplacian on the processing target image data, the processing target image G (see FIG. 4A) is converted into an edge. It is separated into an edge layer that includes a portion and a non-edge layer NEL that does not include an edge portion (see FIG. 4B3). At this time, the edge portion of the edge layer is processed so that, in addition to the detected edge, a region having a color substantially equal to the edge is included. Thereby, for example, the text objects TX1 and TX2 and the graphic object GR included in the processing target image G include the outline of the object and the filled area inside the outline in the edge layer. On the other hand, the image IM having a relatively gentle gradation change is included in the non-edge layer NEL.

  In step S110, from the edge layer, a first edge layer EL1 (see FIG. 4 (b1)) in which the edge layer is expressed in monochrome (K8 bits) and a second edge layer EL2 (in RGB, 8 bits each) are expressed (see FIG. 4B1). 4 (b2)) is generated. As a result, the processing target image G is separated into a total of three layers EL1, EL2, and NEL.

  Next, the CPU 10 performs a process of compressing the data amount for each separated layer (step S120). Here, compression processing by binarization of the number of gradations is performed for the first edge layer EL1, compression processing by low resolution is performed for the second edge layer EL2, and low resolution is performed for the non-edge layer NEL. And compression processing by irreversible compression such as JPEG. Accordingly, the first edge layer EL1 subjected to the binarization compression process (see FIG. 4C1), and the second edge layer EL2 subjected to the low resolution compression process (refer to FIG. 4C2). , And a non-edge layer NEL (see FIG. 4C3) subjected to resolution reduction and lossy compression. As described above, in step S120, processing is performed for each of the three layers EL1, EL2, and NEL so that an appropriate compression format is properly used according to the type of the layer.

  Next, the CPU 10 performs a character extraction process on the first edge layer EL1 (step S130). Thereby, as shown in FIG. 5 as an example, the characters TX1 and TX2 included in the first edge layer EL1 are extracted from the first edge layer EL1 (see FIG. 5A) (see FIG. 5B). ).

  Next, the CPU 10 generates a layer of text data (hereinafter referred to as “text layer TL”) representing the extracted characters (see step S140, FIG. 5C). In the text layer TL, the extracted characters are represented by text data designating the character position, character type, font, character size, color, and the like. When displaying the image of the image file, the text layer can be designated as a non-display layer to make it a layer unrelated to image display.

  Next, the CPU 10 performs processing for integrating the first edge layer EL1, the second edge layer EL2, and the non-edge layer NEL compressed in step S120, and the text layer TL generated in step S140 into a single file. (Step S150). As a result, as shown in FIG. 6, an image file GF in a multilayer data format having a data structure including the header information H of the file, the first edge layer EL1, the second edge layer EL2, the non-edge layer NEL, and the text layer TL. Is generated.

  Next, the CPU 10 stores the generated image file GF in a designated area on the HD 40, and performs a save process for the image file GF (step S160). When the storage process is performed, the file generation process in FIG. 3 is terminated.

  Note that step S110 is processing performed by the CPU 10 as the layer separation unit 71, step S120 is processing performed by the CPU 10 as the layer compression unit 72, steps S130 and S140 are processing performed by the CPU 10 as the text layer generation unit 73, and step S150 is processing performed by the CPU 10 as a layer. This corresponds to the processing performed as the integration unit 74.

  Next, the file browsing process performed by the file browsing application 80 will be described in detail according to the flowchart of FIG.

  For example, when the user operates the mouse 2 or the keyboard 3 to specify the image file GF recorded in the HD 40 and instruct the file browsing application 80 to display the image file GF, the file browsing process of FIG. Is started.

  When the file browsing process is started, the CPU 10 reads the image file GF stored in the HD 40 (step S200), performs a process of superimposing the layers of the image file GF, and outputs the processed image data to the display 4. Thus, an image in which each layer overlaps is displayed (step S210). More specifically, the CPU 10 reads the data of the first edge layer EL1 and the second edge layer EL2 from the HD 40, except for the text layer designated not to be displayed. After the read data is decompressed, the text / graphics layer is restored by using the corresponding color of the second edge layer EL2 as the pixel value for the pixel that is edged in the first edge layer EL1. The (Parts corresponding to TX1, TX2, and GR in FIG. 4A). Then, the restored text / graphic layer and the NEL layer obtained by decompressing the non-edge layer NEL saved as an image file are superimposed, and the display 4 is displayed. To display.

  Next, the CPU 10 determines whether or not a character search instruction has been received (step S220). Here, it is determined whether or not a user instruction for performing a text search for the image file GF is received from the mouse 2 or the keyboard 3, and if a character search instruction is received (step S220: Yes), step S230 is performed. Proceed to If no character search instruction has been received (step S220: No), the process proceeds to step S250.

  When the process proceeds to step S230, the CPU 10 refers to the text layer TL of the image file GF and searches for a search target character or character string. Here, since the text layer TL is described by text data, the text layer TL is processed by searching the text data for a data portion that matches the character or character string to be searched.

  The search result screen is displayed on the display 4 via the display I / F 60 (step S240), and the process proceeds to step S250.

  When the process proceeds to step S250, the CPU 10 determines whether or not to end the browsing process of the image file GF. A determination is made based on whether or not an instruction to end the browsing process is input by the user operating the mouse 2 or the keyboard 3. When the browsing process is not ended (step S250: No), the process returns to step S220 and the processes after step S220 are repeated. When the browsing process is terminated (step S250: Yes), the process of FIG. 7 is terminated.

  Steps S200, S210, and S250 correspond to processing performed by the CPU 10 as the display processing unit 81, and steps S220 to S240 correspond to processing performed by the CPU 10 as the search processing unit 82.

  As described above, the file generation application 70 includes an image in a multilayer data format in which the image file GF includes a text layer TL that represents characters included in the processing target image G in the text data format from the image data to be processed. A file GF is generated. Thereby, the file browsing application 80 can perform a character search for the image file GF using the text data of the text layer TL. According to the present embodiment, the following effects can be obtained.

  (1) The image file GF generated by the file generation application 70 includes a text layer TL in addition to the plurality of layers EL1, EL2, and NEL separated and compressed from the processing target image G. Although it is a multi-layer data format, it is easy to handle characters due to the text layer TL. For example, the file browsing application 80 can perform character search using text data with reference to the text layer TL of the image file GF, and refers to a plurality of separated layers when performing character search. Thus, it is not necessary to perform complicated processing such as pattern matching on each layer. Therefore, the amount of calculation required for character search is reduced, and character search processing can be performed easily and at high speed. As described above, according to the file generation application 70, it is possible to obtain an image file GF in a multilayer data format that is easy to handle with respect to characters and is easy to use.

  (2) Since the first edge layer EL1 is binarized, the second edge layer EL2 is reduced in resolution, and the non-edge layer NEL is subjected to compression processing by reduction in resolution and lossy compression, the image file GF The edge is expressed with high resolution by the first edge layer EL1 while greatly reducing the amount of data. Therefore, it is possible to obtain an image file GF having a suitable image quality with high edge reproducibility while greatly reducing the data amount.

  (3) Character extraction processing is performed on the first edge layer EL1 with little edge degradation, so that characters to be included in the text layer TL are extracted. Therefore, the accuracy of character extraction can be improved. Therefore, an image file GF including a text layer TL that accurately represents characters included in the processing target image G can be obtained.

  (4) Since the text layer TL is represented by text data, the character search of the image file GF can be performed at high speed. Further, the search process is not limited to the search process by the file browsing application 80, and the character search can be performed at high speed by using a search function of general-purpose software such as an operation system.

(Second embodiment)
Next, a second embodiment will be described. In the first embodiment, the text data text layer TL is generated and included in the image file GF. In the second embodiment, outline data is generated as a character layer and included in the image file GF. Process. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 8 is a diagram illustrating a functional configuration of the image processing apparatus 100 according to the second embodiment. As illustrated in FIG. 8, the file generation application 70 includes a layer separation unit 71, a layer compression unit 72, an outline layer generation unit 75, and a layer integration unit 74. That is, the image processing apparatus 100 has an outline layer generation unit 75 instead of the text layer generation unit 73 as compared with the first embodiment.

  The outline layer generation unit 75 converts outlines such as characters and figures included in the first edge layer EL1 into outline data by using a vector data format described by vector information, and generates an outline layer of outline data.

  FIG. 9 shows an example of processing for generating an outline layer. As shown in FIG. 9, the outline layer generation unit 75 performs outline processing on the first edge layer EL1 including the text objects TX1 and TX2 and the graphic object GR, so that the objects TX1, TX2, GR Is generated in the vector data format. In the outline layer OL, for text object TX1, in addition to vector information obtained by tracing the outline of the character, designation information of the color for filling the inside of the outline is also described.

  When a plurality of characters having the same attribute other than the character size are included in the first edge layer EL1, the outline layer generation unit 75 describes vector information for one reference character among the plurality of the same characters. However, redundant information is reduced by describing magnification information for a reference character without describing vector information for other characters. In the example of FIG. 9, vector information and color designation information are described in the outline layer OL for the text object TX1, but for an object TX2 that differs only in character size from the object TX1, the magnification information for the object TX1 is outlined. Described in the layer OL.

  Then, the layer integration unit 74 integrates the outline layer OL generated by the outline layer generation unit 75 with the compressed first edge layer EL1, second edge layer EL2, and non-edge layer NEL to generate an image file GF. Is generated.

  According to the second embodiment, in addition to the effect (2) in the first embodiment, the following effects can be further obtained.

  (5) Since the image file GF generated by the file generation application 70 includes the outline layer OL, the outline layer OL is included in the multi-layer data format, so that it becomes easy to handle characters and figures. For example, the process of searching for characters and graphics by the search processing unit 82 can be performed simply and at high speed by referring to the outline layer OL. Therefore, it is possible to obtain an image file GF in a multilayer data format that is easy to handle characters and is easy to use.

  (6) Since the characters included in the processing target image G are described in the vector data format in the outline layer OL, an image file GF with high character quality can be obtained. For example, when the file browsing application 80 performs processing for displaying the contents of the character portion of the image file GF, high-quality characters in the vector data format can be displayed. Moreover, since it is a vector data format, high-quality characters can be displayed even when the display magnification of the display process is changed.

  (7) When a plurality of characters having the same attribute other than the character size are included in the first edge layer EL1, the outline layer OL includes vector data for only one reference character, and other characters Since the magnification information for the reference character is described, the data amount of the outline layer OL is reduced. Therefore, the data amount of the image file GF can be further reduced.

  The first embodiment and the second embodiment of the file generation program and the image processing apparatus have been described above. However, the present invention is not limited to these forms, and the following modifications may be made.

  (Modification 1) In the first embodiment, the text layer TL is generated from the first edge layer EL1, and in the second embodiment, the outline layer OL is generated from the first edge layer EL1. As an example, an image file GF having both the text layer TL and the outline layer OL may be generated. For example, a portion of the first edge layer EL1 in which characters can be extracted by the character extraction processing may be used as the text layer TL, and a portion including characters that cannot be recognized by the character extraction processing may be provided as the outline layer OL.

  (Modification 2) In the above embodiment, the processing target image G is separated into the edge layer EL and the non-edge layer NEL, and further, the first edge layer EL1, the second edge layer EL2, and the non-edge layer NEL are divided into three. However, the layer structure is not limited to this. For example, the processing may be performed with the edge layer EL and the non-edge layer NEL as they are without being separated into the first edge layer EL1 and the second edge layer EL2.

  (Modification 3) In the above embodiment, characters are extracted from the first edge layer EL1, but the method of generating the text layer TL is not limited to this. For example, before separation into layers, a character extraction process may be performed on the processing target image G to separate a layer representing a text image and a layer other than text. In this case, the text file TL may be generated from the layer representing the text image to generate the image file GF. When the image data to be processed is in a data format that describes objects such as text, graphics, and images included in the image to be processed G, the text layer TL is generated based on the description of the text object. May be.

  (Modification 4) In the second embodiment, the outline layer OL is generated from the outline data of the first edge layer EL1, but the character is extracted by performing character extraction processing on the first edge layer EL1. The outline layer OL may be generated from the outline data of the characters.

1 is a diagram illustrating a hardware configuration of an image processing apparatus according to a first embodiment. The figure which showed the functional structure of the image processing apparatus. The flowchart which showed the flow of the file generation process. The figure which showed the process example of the process which performs layer separation and compression. The figure which showed the process example of the process which produces | generates a text layer. The figure which showed the data structure of the image file. The flowchart which showed the flow of the file browsing process. The figure which showed the functional structure of the image processing apparatus which concerns on a 2nd Example. The figure which showed the process example of the process which produces | generates an outline layer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image processing apparatus which concerns on 1st Example, 10 ... CPU, 20 ... ROM, 30 ... RAM, 40 ... Hard disk, 50 ... Input I / F, 60 ... Display I / F, 70 ... File generation application, 71 A layer separation unit as a layer separation unit, 72 a layer compression unit as a compression unit, 73 a text layer generation unit as a character layer generation unit, 74 a layer integration unit as an image file generation unit, 75 an outline layer generation , 80 ... file browsing application, 81 ... display processing unit, 82 ... search processing unit, 100 ... image processing apparatus according to the second embodiment, GP ... file generation program, RP ... file browsing program, G ... image to be processed EL1... First edge layer as an image layer, EL2. The second edge layer of Te, non-edge layer of as NEL ... image layer, TL ... text layer as a character layer, GF ... image file, OL ... outline layer.

Claims (6)

A file generation program for generating an image file representing an image by a plurality of layers from image data representing an image to be processed,
Computer
Layer separation means for separating an image represented by the image data into a plurality of image layers including at least an image layer representing an edge portion in the image ;
Character layer generation means for extracting characters included in the image represented by the image data based on the image layer representing the edge portion, and generating a character layer representing the extracted characters;
Compression means for performing compression processing on each of the plurality of image layers;
Integrating the plurality of compressed image layers and the character layer to function as image file generation means for generating the image file ;
The compression means performs a compression process with a higher edge reproducibility than the compression process for other image layers by a compression process that reduces the number of gradations for the image layer representing the edge portion among the plurality of image layers, A file generation program that performs compression processing for reducing the resolution of other image layers . The file generation program according to claim 1,
The file generation program, wherein the character layer generation means generates the character layer representing the extracted characters in a text data format. In the file generation program according to claim 1 or 2 ,
The file generation program, wherein the character layer generation means generates the character layer representing the extracted character in a vector data format. The file generation program according to claim 3 ,
When a plurality of characters having character attributes that differ only in character size are extracted, the character layer generation means describes at least one character of the plurality of characters in a vector data format, and for other characters, vector data A file generation program for generating the character layer by describing a magnification of a character size with respect to a character represented by. Layer separation means for separating an image represented by image data to be processed into a plurality of image layers including at least an image layer representing an edge portion in the image ;
Character layer generation means for extracting characters included in the image represented by the image data based on the image layer representing the edge portion, and generating a character layer representing the extracted characters;
Compression means for performing compression processing on each of the plurality of image layers;
Image file generating means for integrating the plurality of compressed image layers and the character layer to generate an image file including the plurality of image layers and the character layer , and
The compression means performs a compression process with a higher edge reproducibility than the compression process for other image layers by a compression process that reduces the number of gradations for the image layer representing the edge portion among the plurality of image layers, An image processing apparatus that performs compression processing to reduce resolution for other image layers . Separating an image represented by image data to be processed into a plurality of image layers including at least an image layer representing an edge portion in the image;
Extracting characters included in the image represented by the image data based on the image layer representing the edge portion, and generating a character layer representing the extracted characters;
Performing a compression process on each of the plurality of image layers;
Integrating the plurality of compressed image layers and the character layer to generate an image file including the plurality of image layers and the character layer ; and
Among the plurality of image layers, the image layer representing the edge portion is subjected to compression processing for reducing the number of gradations, and compression processing having higher edge reproducibility than compression processing for other image layers is performed, and other image layers are Is an image processing method characterized by performing a compression process for reducing the resolution .

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