JP6206641B2 - Electronic document file compression device - Google Patents

Description

  The present invention relates to compression of an electronic document file, and more particularly to a technique for performing efficient compression without reducing the resolution of a portion that requires sharpness.

  PDF (Portable Document Format (registered trademark)) proposed by Adobe Systems as a standard method for electronic documents has become an ISO standard, and beyond the use of enabling the original printed output to be viewed on the screen, at the high end It has become widespread in a wide range of fields, from data exchange in the printing plate making field to document browsing on a portable information terminal at the low end. In the printing plate making field, data exchange may be performed by embedding a high-definition image or character font as much as possible without considering restrictions on the amount of data. However, in applications where browsing is performed on an electronic book terminal or tablet terminal that has a smaller screen and processing capability than a PC, the amount of data cannot be increased so much that a new problem has arisen in terms of display quality.

  The printed image may include caption characters in addition to the text of the body, and recently, a computer screen captured as an image is often used, and a small character such as a menu screen is often added. For captions in such images, the printed material can often be read by enlarging with a loupe, but on the display screen, if zoom processing equivalent to a loupe is performed, the pixels become mosaic and the case where it cannot be read stands out. became. In order to make caption characters in such an image readable on the display screen, it is necessary to set the original image resolution relatively high and to increase the compression rate (low quality). In this case, there is a problem that mosquito noise becomes conspicuous in the outline portion of the character portion in the image, and the design aesthetics are impaired.

  FIG. 7 shows a display example in which an original image in which characters are expressed as contents and an image expanded after compression are compared. 7A showing the original image and FIG. 7B showing the image expanded after compression, it can be seen that the mosquito noise is conspicuous in the image expanded after compression in FIG. 7B. This mosquito noise is caused by compression using DCT (Discrete Cosine Transform) encoding such as JPEG encoding method, and is not generated in the conventional printed matter not using DCT encoding, and is a phenomenon peculiar to electronic documents. Therefore, it gives the impression that the quality is inferior to the printed matter.

  The JPEG encoding method employs a method of performing DCT encoding independently for each block of 8 × 8 pixels (color component is 16 × 16 pixels). Therefore, two types of noise are generated in principle: block noise (also referred to as block distortion) in which a step is generated between blocks, and mosquito noise that is generated due to the lack of high-frequency components during DCT decoding. These problems have been known since the time when the JPEG encoding method was developed, and an encoding method called JPEG2000 which improved the problem has been proposed. In JPEG2000, wavelet transform is used instead of DCT in JPEG, and superiority in quality is recognized. However, considering the problem in terms of calculation cost, the cost merit is one more and standardization is proceeding. However, the spread did not progress easily. The PDF document also supports JPEG2000 in the standard, but it is not always equipped with a JPEG2000 decoder on the terminal side, so it is recommended to use conventional JPEG when creating a PDF. In addition, a technique has been proposed in which block noise and mosquito noise in an image subjected to JPEG decoding are reduced by image processing to sharpen the image (see Patent Documents 1-3).

Japanese Patent No. 4002599 Japanese Patent No. 4457346 JP 2011-182093 A

  However, in any of the techniques described in Patent Documents 1-3, in order to apply these techniques to JPEG images in a PDF document, it is necessary to implement these techniques in PDF viewing software. There is a problem that it is difficult to reduce mosquito noise only by using existing PDF browsing software such as Adobe Reader which is currently popular. On the other hand, PDF supports lossless compression such as ZIP that generates less mosquito noise in addition to lossy compression such as JPEG and JPEG2000. However, when reversible compression is used, there is a problem that the amount of data is enlarged (in some cases, it may increase from before compression). This problem also occurs when encoding an electronic document file other than PDF when an image is attached.

  Therefore, the present invention uses a lossless image compression method suitable for an encoded electronic document file after encoding, and can reduce the data amount of the entire electronic document file while suppressing the occurrence of mosquito noise in the image. It is an object of the present invention to provide a simple electronic document file compression apparatus.

  In order to solve the above-mentioned problem, the invention according to claim 1 is an apparatus for compressing an electronic document file to which original image data is attached, and defines blank image data according to a page resolution defined in the electronic document file. Image data defining means, and at least one document object is sequentially extracted from the character code, font data, graphic data, and component image data from the electronic document file, and the specified font data is referred to for the character code The character raster data is converted into character raster data and the designated area of the blank image data is replaced with the converted character raster data. The graphic data is converted into graphic raster data and the blank image data is designated. Replace the area with the converted graphic raster data, and specify the part image data. The blank image data is updated by performing a process of replacing the designated area of the blank image data with the converted component image data while referring to the mask data attached with the converted magnification and angle. Image updating means for creating updated image data, and reducing the depth of each gradation of RGB to a predetermined depth or less (for example, 16 gradations or less) with respect to the updated image data, thereby determining the total number of colors Color number reduction means for creating color number reduced image data reduced to a number below (eg 256 colors or less) and reversible compression (eg ZIP) on the color number reduced image data to produce compressed image data An electronic document file, comprising: an image compressing unit that converts the compressed image data into a predetermined electronic document format (for example, PDF). Providing compressor Le.

  According to the first aspect of the present invention, blank image data is defined according to the page resolution defined in an electronic document file (for example, Illustrator (registered trademark)), and character codes, font data, graphic data, components are defined from the electronic document file. Document objects such as image data are sequentially extracted and converted to character raster data while referring to the specified font data for the character code to replace the specified area of the blank image data with the converted character raster data. The graphic data is converted to graphic raster data and the specified area of the blank image data is replaced with the converted graphic raster data, and the part image data is converted at the specified magnification and angle. The specified area of the blank image data was converted while referring to the attached mask data. By performing the process of replacing the product image data, the blank image data is updated to create updated image data, and the depth of each RGB gradation is equal to or less than a predetermined depth (for example, 16 gradations) for the updated image data. The color number reduced image data is generated by reducing the total number of colors to a predetermined number or less (for example, 256 colors or less) by reducing the number of colors to the following), and reversible compression (for example, ZIP) is performed on the color number reduced image data. Since the compressed image data is generated and the compressed image data is converted into a predetermined electronic document format (for example, PDF), generation of mosquito noise can be suppressed and the data amount of the entire electronic document file can be reduced. It becomes possible.

  According to a second aspect of the present invention, in the electronic document file compression apparatus according to the first aspect of the present invention, the depth of each RGB gradation is predetermined for the original image data attached to the electronic document file. Second color number reduction means for creating second color number reduced image data in which the total number of colors is reduced to a predetermined number or less (for example, 256 colors or less) When the resolution of the second color number reduced image data exceeds a predetermined resolution which is a predetermined resolution, the second color number reduced image data is set to a set resolution which is a resolution set to a value lower than the predetermined resolution. Image resolution conversion means for performing resolution conversion so that the second color number reduced image data converted by the image resolution conversion means or the image resolution conversion means does not perform resolution conversion. Any one of the second color-reduced image data is subjected to reversible compression (for example, ZIP) to generate compressed image data; and the second compressed image data is stored in the electronic document file. A second document encoding means for converting the electronic document file into an encoded electronic document file in a predetermined electronic document format (for example, PDF), in a state where the electronic document file is pasted instead of the past original image data; Data amount comparing means for comparing the data amount of the electronic document file and the data amount of the electronic document file, wherein the data amount of the encoded electronic document file is greater than or equal to a predetermined ratio with respect to the data amount of the electronic document file In this case, the image data defining means, the image updating means, the color number reducing means, the image compressing means, and the document encoding means are executed.

  According to the second aspect of the present invention, the RGB gradations are reduced to a predetermined depth or less (for example, 16 gradations or less) with respect to the original image data attached to the electronic document file (for example, Illustrator). Thus, when the second color number reduced image data is generated by reducing the total number of colors to a predetermined number or less (for example, 256 colors or less), and the resolution of the second color number reduced image data exceeds the predetermined resolution, the second color number Resolution conversion is performed so that the reduced image data has a set resolution (<predetermined resolution), and either the color-reduced image data that has undergone resolution conversion or the color-reduced image data that has not undergone resolution conversion is reversible. Compression (for example, ZIP) is performed to create second compressed image data. The second compressed image data is pasted in place of the original image data pasted in the electronic document file, and a predetermined electronic Is converted into a document format (for example, PDF), and the data amount of the encoded electronic document file is compared with the data amount of the electronic document file so that the data amount of the encoded electronic document file is greater than or equal to a predetermined ratio with respect to the data amount of the electronic document file In some cases, the encoded electronic document file is created by the processing by the image data defining means, the image updating means, the color number reducing means, the image compressing means, and the document encoding means in the invention according to claim 1. If the compression method that maintains the quality of images and graphics at a high resolution and the full-text search is possible with embedded character codes, sufficient compression can be performed using an efficient compression method. Become.

  In the invention according to claim 3, the document encoding means sets the character code extracted from the electronic document file by the image update means to a non-drawing attribute, and maintains the designated allocation position while maintaining the specified allocation position. After being added to the document file, it is converted into a predetermined electronic document format.

  According to the invention of claim 3, after the character code extracted from the electronic document file is set to the non-drawing attribute and added to the electronic document file while maintaining the designated allocation position, the electronic document format such as PDF Therefore, when an electronic document file such as a PDF file is used, a full text search using a character code set to a non-drawing attribute is possible.

  In the invention according to claim 4, the image compression means is reversible with respect to the color number reduced image data when the data amount of the compressed image data is larger than a predetermined ratio compared to the color number reduced image data. Instead of performing compression (for example, ZIP), irreversible compression (for example, JPEG) is performed based on a predetermined compression strength to generate irreversible compressed image data.

  According to the fourth aspect of the present invention, when the data amount of the compressed image data is larger than a predetermined ratio compared to the color number reduced image data, instead of performing reversible compression such as ZIP on the color number reduced image data. Since irreversible compression such as JPEG is performed based on a predetermined compression rate and irreversible compressed image data is created, it is possible to prevent the data amount from increasing without limit.

  According to the present invention, it is possible to reduce the data amount of the entire electronic document file while using a lossless image compression method suitable for the encoded electronic document file after encoding and suppressing the occurrence of mosquito noise in the image. It becomes.

It is a hardware block diagram of the compression apparatus of the electronic document file which concerns on one Embodiment of this invention. 1 is a functional block diagram showing a configuration of an electronic document file compression apparatus according to a first embodiment of the present invention. It is a flowchart which shows the process outline | summary of the compression apparatus of the electronic document file which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the color number reduction in step S13, S25. It is a functional block diagram which shows the structure of the compression apparatus of the electronic document file which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the process outline | summary of the compression apparatus of the electronic document file which concerns on the 2nd Embodiment of this invention. It is a figure which shows the example of a display which compared the original image in which the character was expressed as a content, and the image expanded after compression. It is a functional block diagram which shows the structure of the compression apparatus of the electronic document file which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows the process outline | summary of the compression apparatus of the electronic document file which concerns on the 3rd Embodiment of this invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
<1. First Embodiment>
<1.1. Device configuration>
FIG. 1 is a hardware configuration diagram of an electronic document file compression apparatus according to the first embodiment of the present invention. The electronic document file compression apparatus according to this embodiment can be realized by a general-purpose computer. As shown in FIG. 1, a CPU (Central Processing Unit) 1 and a RAM (Random Access Memory) which is a main memory of the computer. ) 2, a large-capacity storage device 3 such as a hard disk or flash memory for storing programs and data executed by the CPU 1, a key input I / F (interface) 4 such as a keyboard and a mouse, a data storage medium, etc. A data input / output I / F (interface) 5 for data communication with the external device and a display unit 6 which is a display device such as a liquid crystal display are connected to each other via a bus.

  FIG. 2 is a functional block diagram showing the configuration of the electronic document file compression apparatus according to this embodiment. In FIG. 2, 10 is a color number reduction unit, 20 is an image resolution conversion unit, 30 is an image compression unit, 50 is a document encoding unit, 60 is an electronic document file storage unit, and 70 is an encoded electronic document file storage unit. .

  The color number reduction means 10 performs processing for reducing the number of colors and creating color number reduced image data for the original image data attached to the electronic document file stored in the electronic document file storage means 60. The image resolution conversion means 20 performs resolution conversion on the color number reduced image data. The image compression means 30 performs reversible compression such as ZIP compression on both the color-reduced image data whose resolution has been converted by the image resolution conversion means 20 and the color-reduced image data that has not been resolution-converted. Process to create. The document encoding means 50 converts the encoded image data into a state of being attached to the electronic document file in place of the original image data attached to the electronic document file, converts it into a predetermined electronic document format, and encodes it. Do.

  The electronic document file storage unit 60 is a storage unit that stores an electronic document file that is an electronic document that can be processed by a computer, and is realized by the storage device 3. The electronic document file stored in the electronic document file storage means 60 is an MS-Word (registered trademark) .doc, PowerPoint (registered trademark) .ppt, Illustrator (registered trademark) as long as it is an electronic document with image data attached thereto. ) .Ai, InDesign (registered trademark) .ind, etc., can be used in various formats. Here, “attaching” means that the image data is logically related to the electronic document file. As long as it is logically related, a specific aspect is not limited. The encoded electronic document file storage unit 70 is a storage unit that stores an encoded electronic document file that is a compression-encoded electronic document file, and is realized by the storage device 3. Various types of encoded electronic document files can be used, but in this embodiment, the PDF format, which is a general-purpose format, is used. The color number reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, and the document encoding unit 50 are realized by the CPU 1 executing a program stored in the storage device 3.

  Each component shown in FIG. 2 is actually realized by installing a dedicated program in hardware such as a computer and its peripheral devices as shown in FIG. That is, the computer executes the contents of each means according to a dedicated program. In this specification, a computer means a device that has an arithmetic processing unit such as a CPU and is capable of data processing, and has a screen size and a resolution that can confirm image quality, and performs image resolution conversion and compression. This is a desktop or notebook personal computer having a CPU and a storage device having a calculation speed capable of processing image calculation such as treatment at a practical response speed.

  The storage device 3 shown in FIG. 1 is mounted with a dedicated program for operating the CPU 1 and causing the computer to function as an electronic document file compression device. By executing this dedicated program, the CPU 1 realizes functions as the color number reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, and the document encoding unit 50. The storage device 3 not only functions as the electronic document file storage unit 60 and the encoded electronic document file storage unit 70 but also stores various data necessary for processing as an electronic document file compression device.

<1.2. Processing action>
Next, the processing operation of the electronic document file compression apparatus shown in FIGS. 1 and 2 will be described. FIG. 3 is a flowchart showing an outline of processing of the electronic document file compression apparatus according to the first embodiment of the present invention. First, the color number reduction unit 10 extracts a document object from the electronic document file stored in the electronic document file storage unit 60 (step S11). Specifically, document objects such as character codes, graphic data, and image data attached to the electronic document file are extracted according to the format of the electronic document file.

  Next, the color number reduction means 10 determines whether or not the extracted document object is image data (step S12). If it is determined that the extracted document object is image data, it indicates that the extracted document object is original image data attached to the electronic document file. The document object is set as original image data, and the number of colors is reduced with respect to the original image data (step S13). Specifically, the total number of colors is reduced by lowering the gradation of each color such as RGB.

  FIG. 4 is a diagram for explaining the color number reduction processing in step S13. 4A shows a bit arrangement of original pixels constituting the original image data, and FIG. 4B shows a bit arrangement of pixels constituting the color number reduced image data. As shown in FIG. 4A, in this embodiment, since the original image data represents each color of R, G, and B with 8 bits, each color has a depth of 256 gradations. In the color number reduction process in step S13, the color number reduction means 10 reduces R to 3 bits and 8 gradations, G to 3 bits and 8 gradations, and B to 2 bits and 4 gradations. As a result, as shown in FIG. 4B, 8-bit 256 color-reduced image data is obtained as a whole. In the example of FIG. 4, the R, G, and B gradations are reduced to 1/32, 1/32, and 1/64, respectively. The image data is encoded from 24 bits to 8 bits per pixel, and a new color lookup table (pixel index value to RGB value conversion table) is defined and attached. In addition to the method shown in FIG. 4, a known color number reduction method can be used. The color number reduction unit 10 is configured to be able to set a plurality of color number reduction methods, and in accordance with the instruction via the key input I / F 4 functioning as the color number reduction method setting unit, the instructed color number reduction method is performed. The color number reduction means 10 is set so as to be executed.

  When the image is compressed and expanded, the mosquito noise is conspicuous when the source image is a monochrome image that is substantially binary and has high contrast, and the generated mosquito noise is halftone. For example, when the source image is a character image in which the background is white and the characters are expressed in black, the generated mosquito noise is white or a gray color close to black. However, if the number of colors is limited from 256 tones, the gray color close to white is approximated to white, and the gray color close to black is approximated to black, so halftone mosquito noise is expressed. Disappear. On the other hand, the monochrome image of the source has 256 gradations in the data format, but there is no problem even if it is reduced to about 4 to 8 gradations in practice. If the gradation is reduced to two gradations, jaggy is generated in the character outline portion, so that four gradations or more are necessary to maintain the anti-aliasing effect. Therefore, in the present embodiment, in the case of a color image, the RGB is reduced from 256 tones to 4 to 8 each, and the number of colors is reduced from about 16 million colors (256 to the cube of 256) to about 256 colors. I am letting.

  Next, the image resolution conversion means 20 determines whether or not the resolution of the color number reduced image data is larger than a predetermined resolution which is a predetermined resolution (step S14). The predetermined resolution can be appropriately set according to the situation. If it is determined in step S14 that the resolution of the color number reduced image data is greater than the predetermined resolution, the image resolution conversion means 20 sets the resolution of the color number reduced image data to a preset resolution that is a preset resolution. (Step S15). Specifically, a process of reducing the color number reduced image data at a ratio of (set resolution) / (resolution of the color number reduced image data) is performed. As a result, color-reduced image data with a reduced number of pixels and reduced resolution is obtained. Various known techniques such as nearest neighbor, bilinear, bicubic, and the like can be used as a technique for reducing the number of color-reduced image data in order to reduce the resolution. The cubic method is adopted.

  By steps S14 and S15, only when the resolution of the color number reduced image data is larger than the predetermined resolution, the resolution of the color number reduced image data is converted to be smaller. For this reason, the resolution of the color-reduced image data is always equal to or lower than the predetermined resolution, and the data amount can be reduced while maintaining a resolution that is easy to see to some extent. As a relationship between the predetermined resolution and the set resolution, if the condition that the predetermined resolution is larger than the set resolution is satisfied, it can be appropriately set within the range of this condition. In the present embodiment, the set resolution is multiplied by 1.5. Is set to a predetermined resolution. Therefore, for example, when the set resolution is 300 PPI (Pixel Per Inch) and the predetermined resolution is 450 PPI, the color-reduced image data whose resolution exceeds 450 PPI is converted to 300 PPI.

  The reason for setting the predetermined resolution by multiplying the set resolution by 1.5 is that if the resolution of the read image data has a fraction such as 301 PPI and the predetermined resolution is 300 PPI, the process proceeds to step S15 and resolution conversion processing is performed. End up. Even if the bicubic method is used, the resolution conversion process cannot avoid deterioration of the image quality, and is preferably not performed as much as possible. Therefore, if the resolution of the read color-reduced image data is within the boundary range of 301 to 450 PPI, the value of the predetermined resolution is made slightly larger than the set resolution so as not to proceed to step S15.

  Next, the image compression means 30 performs compression encoding of the color number reduced image data (step S16). In step S16, both the color-reduced image data whose resolution has been converted by the image resolution conversion means 20 and the color-reduced image data whose resolution has not been converted are both compressed using the lossless compression method to create compressed image data. . As the lossless compression method, various known methods can be used, but in this embodiment, the ZIP method is used.

  In step S16, the image compression means 30 further determines whether or not the data amount of the created compressed image data is larger than the data amount of the color number reduced image data before compression multiplied by a predetermined ratio. The predetermined ratio is preferably 25% or more and 75% or less. In the present embodiment, the predetermined ratio is set to “50%”. If the data amount of compressed image data is larger than the data amount of color-reduced image data before compression multiplied by a predetermined ratio, the color-reduced image data before compression is compressed using the lossy compression method. Created as compressed image data. The compression strength is set at a predetermined compression strength set in advance. As the irreversible compression method, various known methods can be used, but in this embodiment, the JPEG method is used.

  In the case of a full color image, the lossy compression method always has a smaller amount of data than the lossless compression method, but in the case of image data with a reduced number of colors, the reverse is also possible. However, since the irreversible compression method can reduce the data amount more often than the lossless compression method, the data amount of the compressed image data is reduced by the number of colors by the processing of the image compression means 30 in step S16. It is below the value obtained by multiplying the data amount of the image data by a predetermined ratio.

  On the other hand, when it is determined in step S11 that the document object extracted is not image data, the processes in steps S13 to S16 are not performed on the document object. Each time processing for one document object is completed, it is determined whether processing has been completed for all document objects (step S17). If the processing has not been completed for all document objects, the process returns to step S11 to extract the next document object. When the processing is completed for all the document objects, the document encoding unit 50 performs encoding processing of the electronic document file (step S18).

  Various known formats can be used for the encoding process of the electronic document file, but in this embodiment, the PDF format is used. Specifically, the compressed image data is pasted into an electronic document file in the same manner as other document objects, and converted into an encoded electronic document file such as a PDF format. This process is performed using an algorithm similar to a known PDF conversion application such as Acrobat (registered trademark).

<2. Second Embodiment>
<2.1. Device configuration>
Next, an electronic document file compression apparatus according to the second embodiment of the present invention will be described. FIG. 5 is a functional block diagram showing the configuration of the electronic document file compression apparatus according to the second embodiment. In the second embodiment, the hardware configuration is the same as that of the first embodiment, as shown in FIG. In FIG. 5, 11 is an image definition means, 21 is an image update means, 31 is a color number reduction means, 41 is an image compression means, 51 is a document encoding means, 61 is an electronic document file storage means, and 71 is an encoded electronic document. File storage means.

  The image definition means 11 defines blank image data according to the resolution defined in the electronic document file. The image update unit 21 extracts a document object from the electronic document file and performs raster conversion (bitmap conversion) to update the blank image data and create updated image data. The color number reduction unit 31 performs a process of reducing the number of colors and creating color number reduced image data for the updated image data updated by the image update unit 21. The image compressing unit 41 performs a process of creating a compressed image data by performing lossless compression such as ZIP compression on the color number reduced image data whose color number has been reduced by the color number reducing unit 31. The document encoding unit 50 performs processing for converting the compressed image data compressed by the image compression unit 41 into a predetermined electronic document format to obtain an encoded electronic document file.

  Similar to the electronic document file storage unit 60 in the first embodiment, the electronic document file storage unit 61 is a storage unit that stores an electronic document file that is an electronic document that can be processed by a computer, and is realized by the storage device 3. . The encoded electronic document file storage unit 71 is a storage unit that stores an encoded electronic document file that is a compression-encoded electronic document file, similar to the encoded electronic document file storage unit 70 in the second embodiment. This is realized by the storage device 3. The image definition unit 11, the image update unit 21, the color number reduction unit 31, the image compression unit 41, and the document encoding unit 51 are realized by the CPU 1 executing a program stored in the storage device 3.

  As in the first embodiment, each component shown in FIG. 5 is actually realized by mounting a dedicated program on hardware such as a computer and its peripheral devices as shown in FIG. . That is, the computer executes the contents of each means according to a dedicated program.

  The storage device 3 shown in FIG. 1 is mounted with a dedicated program for operating the CPU 1 and causing the computer to function as an electronic document file compression device. By executing this dedicated program, the CPU 1 realizes functions as the image definition unit 11, the image update unit 21, the color number reduction unit 31, the image compression unit 41, and the document encoding unit 51. The storage device 3 not only functions as the electronic document file storage unit 61 and the encoded electronic document file storage unit 71 but also stores various data necessary for processing as a compression device for the electronic document file.

<2.2. Processing action>
Next, the processing operation of the electronic document file compression apparatus shown in FIG. 5 will be described. FIG. 6 is a flowchart showing an outline of processing of the electronic document file compression apparatus according to the second embodiment of the present invention. First, the image definition unit 11 acquires an electronic document file stored in the electronic document file storage unit 60. Then, blank image data is defined according to the resolution set in the electronic document file (step S21). Specifically, image data having an image size (number of pixels) according to the set resolution is set, and a storage area for pixel values corresponding to each pixel is secured in the RAM 2. Blank image data means normal image data in form, but the value of each pixel of the image data has no meaning.

  Next, the image update means 21 extracts a document object from the electronic document file (step S22). Specifically, document objects such as character codes, graphic data, and component image data attached to the electronic document file are extracted according to the format of the electronic document file. The component image data is image data as a document object that is one component of an electronic document file. Subsequently, the image update unit 21 updates the blank image data while performing raster conversion on the extracted document object (step S23). Specifically, the character code is converted to character raster data while referring to the specified font data, the specified area of the blank image data is replaced with the converted character raster data, and the graphic data is converted. On the other hand, it is converted into graphic raster data to replace the specified area of the blank image data with the converted graphic raster data, and the part image data is converted and attached at the specified magnification and angle. The blank image data is updated by repeating the process of replacing the designated area of the blank image data with the converted component image data while referring to the mask data.

  Each time the processing for one document object is completed, the image update unit 21 determines whether the processing has been completed for all document objects (step S24). If the processing has not been completed for all document objects, the process returns to step S22 to extract the next document object. When processing is completed for all document objects, updated blank image data is obtained as updated image data.

  When the update image data is obtained, the color number reduction means 31 performs a color number reduction process on the created update image data (step S25). Specifically, the total number of colors is reduced by lowering the gradation of each color such as RGB. In the updated image data in this embodiment, as shown in FIG. 4A, each color of R, G, and B is expressed by 8 bits, so each color has 256 gradations. In the process of step S25, the color number reduction unit 31 reduces R to 3 bits and 8 gradations, G to 3 bits and 8 gradations, and B to 2 bits and 4 gradations. As a result, as shown in FIG. 4B, 8-bit 256 color-reduced image data is obtained as a whole. As in the first embodiment, a known color number reduction method can be used in addition to the method shown in FIG. The color number reduction unit 31 is configured to be able to set a plurality of color number reduction methods, and in accordance with the instruction via the key input I / F 4 functioning as the color number reduction method setting unit, the instructed color number reduction method is performed. The color number reduction means 31 is set to be executed. The color number reduction method set in the color number reduction unit 10 in the first embodiment and the color number reduction unit 31 in the second embodiment may be the same or different.

  Next, the image compression means 41 performs compression encoding of the color number reduced image data (step S26). Specifically, the color number reduced image data created by the color number reduction means 31 is compressed to create compressed image data. The compression strength is set at a predetermined compression strength set in advance. As the compression method, various known methods can be used, but in this embodiment, the ZIP method which is lossless compression is used.

  In step S26, the image compression means 41 further determines whether or not the data amount of the generated compressed image data is larger than the data amount of the color number reduced image data before compression multiplied by a predetermined ratio. The predetermined ratio is preferably 25% or more and 75% or less, as in the first embodiment. Also in this embodiment, the predetermined ratio is set to “50%” as in the first embodiment. If the data amount of compressed image data is larger than the data amount of color-reduced image data before compression multiplied by a predetermined ratio, the color-reduced image data before compression is compressed using the lossy compression method. Created as compressed image data. The compression strength is set at a predetermined compression strength set in advance. As the irreversible compression method, various known methods can be used, but in this embodiment, the JPEG method is used.

  In the case of a full color image, the lossy compression method always has a smaller data amount than the lossless compression method, but in the case of image data with a reduced number of colors, the opposite case may occur. However, since the irreversible compression method can reduce the data amount more often than the lossless compression method, the data amount of the compressed image data is reduced by the number of colors by the processing of the image compression means 41 in step S26. It is below the value obtained by multiplying the data amount of the image data by a predetermined ratio.

  Next, the document encoding means 51 performs a transparent character addition process (step S27). Specifically, the character code extracted from the electronic document file in step S22 is set as a non-drawing attribute to create transparent character data, and the designated allocation position is maintained and added to the electronic document file. The transparent character data can be created by setting the non-drawing attribute to a known PDF conversion application such as Acrobat (registered trademark). By adding transparent character data, a full-text search using a character code can be performed.

  Next, the document encoding means 51 performs an encoding process for the electronic document file (step S28). Various known formats can be used for the encoding process of the electronic document file, but in this embodiment, the PDF format is used. Specifically, the compressed image data and the transparent character data are converted into an encoded electronic document file in PDF format. This process is performed using an algorithm similar to a known PDF conversion application such as Acrobat.

<3. Third Embodiment>
<3.1. Device configuration>
Next, an electronic document file compression apparatus according to the third embodiment of the present invention will be described. FIG. 8 is a functional block diagram showing the configuration of the electronic document file compression apparatus according to the third embodiment. In the third embodiment, the hardware configuration is the same as that in the first and second embodiments, as shown in FIG. In FIG. 8, components having the same functions as those in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted. Reference numeral 90 denotes a data amount comparison unit, 62 denotes an electronic document file storage unit, and 72 denotes an encoded electronic document file storage unit.

  The electronic document file compression apparatus according to the third embodiment is a combination of the electronic document file compression apparatus according to the first embodiment and the components of the electronic document file compression apparatus according to the second embodiment. is there. Then, after the processing by the color number reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, and the document encoding unit 50, which are constituent elements of the electronic document file compression apparatus according to the first embodiment, is obtained. The data amount of the encoded electronic document file is compared with the data amount of the original electronic document file, and the data amount of the encoded electronic document file is equal to or greater than a predetermined ratio of the data amount of the original electronic document file. In this case, the processing by the image definition unit 11, the image update unit 21, the color number reduction unit 31, the image compression unit 41, and the document encoding unit 51, which are components of the electronic document file compression apparatus according to the second embodiment. Do.

  The electronic document file storage means 62 stores an electronic document file that is an electronic document that can be processed by a computer, similar to the electronic document file storage means 60 in the first embodiment and the electronic document file storage means 61 in the second embodiment. And is realized by the storage device 3. The encoded electronic document file storage means 72 is a compressed and encoded electronic document file, similar to the encoded electronic document file storage means 70 in the first embodiment and the encoded electronic document file storage means 71 in the second embodiment. The storage unit 3 stores the encoded electronic document file, and is realized by the storage device 3. Color number reduction means 10, image resolution conversion means 20, image compression means 30, document encoding means 50, data amount comparison means 90, image definition means 11, image update means 21, color number reduction means 31, image compression means 41, The document encoding means 51 is realized by the CPU 1 executing a program stored in the storage device 3.

  As in the first and second embodiments, each component shown in FIG. 8 is actually equipped with a dedicated program in hardware such as a computer and its peripheral devices as shown in FIG. It is realized by doing. That is, the computer executes the contents of each means according to a dedicated program.

  The storage device 3 shown in FIG. 1 is mounted with a dedicated program for operating the CPU 1 and causing the computer to function as an electronic document file compression device. By executing this dedicated program, the CPU 1 causes the color number reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, the document encoding unit 50, the data amount comparison unit 90, the image definition unit 11, and the image update unit. 21, functions as the color number reduction unit 31, the image compression unit 41, and the document encoding unit 51 are realized. The storage device 3 not only functions as the electronic document file storage unit 62 and the encoded electronic document file storage unit 72 but also stores various data necessary for processing as a compression device for the electronic document file.

<3.2. Processing action>
Next, the processing operation of the electronic document file compression apparatus shown in FIG. 8 will be described. FIG. 9 is a flowchart showing an outline of processing of the electronic document file compression apparatus according to the third embodiment of the present invention. First, the number-of-colors reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, and the document encoding unit 50 execute the processes of steps S11 to S18 shown in FIG. As a result, an encoded electronic document file is obtained.

  When the encoded electronic document file is obtained by the processing of the document encoding means 50, the data amount of the encoded electronic document file is compared with the data amount of the original electronic document file stored in the electronic document file storage means 62. Is performed (step S30). Specifically, the data amount of the encoded electronic document file is compared with a value obtained by multiplying the data amount of the electronic document file by a predetermined ratio. As the predetermined ratio, a value determined to be sufficiently compressed can be set as appropriate, but in this embodiment, 10% is set. Therefore, when the data amount of the encoded electronic document file is 10% or more of the data amount of the electronic document file (step S31), the image definition unit 11, the image update unit 21, the color number reduction unit 31, the image compression unit. 41. The document encoding means 51 executes the processing of steps S21 to S28 shown in FIG.

  The encoded electronic document file obtained by the process of step S28 is stored in the encoded electronic document file storage means 72. In step S31, when the data amount of the encoded electronic document file obtained by the process of step S18 is smaller than 10% of the data amount of the electronic document file, the image definition unit 11, the image update unit 21, the number of colors The processing of steps S21 to S28 is not executed by the reduction unit 31, the image compression unit 41, and the document encoding unit 51, and the encoded electronic document file obtained by the processing of step S18 is the encoded electronic document file storage unit 72. Is remembered. That is, in the third embodiment, when the image data is sufficiently compressed by the processing by the color number reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, and the document encoding unit 50, the obtained encoding is performed at that time. When the electronic document file is used as the compression result and is sufficiently compressed by the processing by the color number reduction unit 10, the image resolution conversion unit 20, the image compression unit 30, and the document encoding unit 50, the image definition unit 11 and the image update unit 21 The color number reduction means 31, the image compression means 41, and the document encoding means 51 perform compression to obtain an encoded electronic document file.

<4. Modified example>
The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made. For example, in the second embodiment, transparent character data is created from the extracted character code and added to the electronic document file. However, this processing is omitted so that transparent character data is not added. May be.

  In the above embodiment, the case where the PDF format is used as the encoded electronic document file has been described as an example. However, any encoded electronic document file to which image data is attached can be handled regardless of the electronic document format. Is possible.

  Further, in the above embodiment, when the data amount of the compressed image data by lossless compression is larger than the data amount of the color number reduced image data before compression multiplied by a predetermined ratio, the color number reduced image data before compression is Thus, the compression is performed by the lossy compression method, but the compressed image data by the lossless compression may be directly encoded into the encoded electronic document file without comparing the data amount before and after the lossless compression. . In particular, when the compression strength is set high (the amount of data is small), the amount of data can be sufficiently reduced without making a comparison.

1 ... CPU (Central Processing Unit)
2 ... RAM (Random Access Memory)
3 ... Storage device 4 ... Key input I / F
5. Data input / output I / F
6 ... Display unit 10 ... Color number reduction means (second color number reduction means)
DESCRIPTION OF SYMBOLS 11 ... Image definition means 20 ... Image resolution conversion means 21 ... Image update means 30 ... Image compression means (2nd image compression means)
31 ... Color number reduction means 41 ... Image compression means 50 ... Document encoding means (second document encoding means)
51 ... Document encoding means 60, 61, 62 ... Electronic document file storage means 70, 71, 72 ... Encoded electronic document file storage means 90 ... Data amount comparison means

Claims (6)

An apparatus for compressing an electronic document file to which original image data is attached,
Image data defining means for defining blank image data according to the page resolution defined in the electronic document file;
At least one document object is sequentially extracted from the electronic document file among the character code, font data, graphic data, and component image data, and the character code is converted into character raster data while referring to the specified font data. Then, the designated area of the blank image data is replaced with the converted character raster data, and the graphic data is converted into graphic raster data to convert the designated area of the blank image data into a converted graphic raster. Replace with the data, and for the part image data, replace the specified area of the blank image data with the converted part image data while referring to the attached mask data after converting at the specified magnification and angle The blank image data is updated to create updated image data. And the image updating means for,
Color number reduction means for creating color number reduced image data in which the total number of colors is reduced to a predetermined number or less by reducing the depth of each RGB gradation to a predetermined depth or less with respect to the updated image data ,
Image compression means for performing lossless compression on the color-reduced image data and creating compressed image data;
Document encoding means for converting the compressed image data into a predetermined electronic document format;
Second color number in which the total number of colors is reduced to a predetermined number or less by reducing the depth of each gradation of RGB to a predetermined depth or less with respect to the original image data attached to the electronic document file Second color number reduction means for creating reduced image data;
When the resolution of the second color number reduced image data exceeds a predetermined resolution which is a predetermined resolution, the second color number reduced image data is set to a set resolution which is a resolution set to a value lower than the predetermined resolution. Image resolution conversion means for converting the resolution into
Reversible compression is performed on either the second color number reduced image data whose resolution has been converted by the image resolution converting means or the second color number reduced image data which has not been converted by the image resolution converting means, A second image compression means for creating compressed image data;
A second document in which the second compressed image data is pasted in place of the original image data pasted on the electronic document file, and the electronic document file is converted into an encoded electronic document file in a predetermined electronic document format. Encoding means;
Data amount comparison means for comparing the data amount of the encoded electronic document file and the electronic document file,
When the data amount of the encoded electronic document file is greater than or equal to a predetermined ratio with respect to the data amount of the electronic document file, the image data definition unit, the image update unit, the color number reduction unit, the image compression unit, the document code electronic document file compression apparatus according to claim Rukoto process by means runs. An apparatus for compressing an electronic document file to which original image data is attached,
Image data defining means for defining blank image data according to the page resolution defined in the electronic document file;
At least one document object is sequentially extracted from the electronic document file among the character code, font data, graphic data, and component image data, and the character code is converted into character raster data while referring to the specified font data. Then, the designated area of the blank image data is replaced with the converted character raster data, and the graphic data is converted into graphic raster data to convert the designated area of the blank image data into a converted graphic raster. Replace with the data, and for the part image data, replace the specified area of the blank image data with the converted part image data while referring to the attached mask data after converting at the specified magnification and angle The blank image data is updated to create updated image data. And the image updating means for,
Color number reduction means for creating color number reduced image data in which the total number of colors is reduced to a predetermined number or less by reducing the depth of each RGB gradation to a predetermined depth or less with respect to the updated image data ,
Image compression means for performing lossless compression on the color-reduced image data and creating compressed image data;
Document encoding means for converting the compressed image data into a predetermined electronic document format;
I have a,
When the data amount of the compressed image data is greater than a predetermined ratio compared to the color-reduced image data, the image compressing unit is configured to perform a predetermined compression strength instead of performing reversible compression on the color-reduced image data. lossy compression alms, electronic document file compression device that you have so as to create a compressed image data lossy characterized based on. In claim 1 or claim 2 ,
The document encoding unit sets the character code extracted from the electronic document file by the image update unit to a non-drawing attribute, adds the character code to the electronic document file while maintaining the designated allocation position, An apparatus for compressing an electronic document file, wherein the electronic document file is converted into a document format. A program for causing a computer to function as the electronic document file compression device according to any one of claims 1 to 3 . A method in which a computer compresses an electronic document file to which original image data is pasted to create a compressed electronic document file,
Second color number in which the total number of colors is reduced to a predetermined number or less by reducing the depth of each gradation of RGB to a predetermined depth or less with respect to the original image data attached to the electronic document file Creating reduced image data; and
When the resolution of the second color number reduced image data exceeds a predetermined resolution which is a predetermined resolution, the second color number reduced image data is set to a set resolution which is a resolution set to a value lower than the predetermined resolution. The resolution conversion stage,
Applying reversible compression to either the second color number-reduced image data whose resolution has been converted by the step of performing the resolution conversion or the second color number-reduced image data which has not been converted by the step of performing the resolution conversion, Creating second compressed image data;
Converting the second compressed image data into an encoded electronic document file in a predetermined electronic document format, with the second compressed image data being attached instead of the original image data attached to the electronic document file;
Comparing the amount of data in the encoded electronic document file and the electronic document file;
Defining blank image data according to the page resolution defined in the electronic document file when the data amount of the encoded electronic document file is equal to or greater than a predetermined ratio with respect to the data amount of the electronic document file;
At least one document object is sequentially extracted from the electronic document file among the character code, font data, graphic data, and component image data, and the character code is converted into character raster data while referring to the specified font data. Then, the designated area of the blank image data is replaced with the converted character raster data, and the graphic data is converted into graphic raster data to convert the designated area of the blank image data into a converted graphic raster. Replace with the data, and for the part image data, replace the specified area of the blank image data with the converted part image data while referring to the attached mask data after converting at the specified magnification and angle The blank image data is updated to create updated image data. The method comprising,
For the updated image data, creating color number reduced image data in which the total number of colors is reduced to a predetermined number or less by reducing the depth of each RGB gradation to a predetermined depth or less;
Applying lossless compression to the color-reduced image data and creating compressed image data;
Converting the compressed image data into a predetermined electronic document format;
A method for creating a compressed electronic document file, comprising: A method in which a computer compresses an electronic document file to which original image data is pasted to create a compressed electronic document file,
  An image data stage for defining blank image data according to the page resolution defined in the electronic document file;
At least one document object is sequentially extracted from the electronic document file among the character code, font data, graphic data, and component image data, and the character code is converted into character raster data while referring to the specified font data. Then, the designated area of the blank image data is replaced with the converted character raster data, and the graphic data is converted into graphic raster data to convert the designated area of the blank image data into a converted graphic raster. Replace with the data, and for the part image data, replace the specified area of the blank image data with the converted part image data while referring to the attached mask data after converting at the specified magnification and angle The blank image data is updated to create updated image data. The method comprising,
For the updated image data, creating color number reduced image data in which the total number of colors is reduced to a predetermined number or less by reducing the depth of each RGB gradation to a predetermined depth or less;
Applying lossless compression to the color-reduced image data and creating compressed image data;
Converting the compressed image data into a predetermined electronic document format;
Have
In the step of creating the compressed image data, when the data amount of the compressed image data is larger than a predetermined ratio compared to the color number reduced image data, instead of performing reversible compression on the color number reduced image data, A method for creating a compressed electronic document file, wherein irreversible compression is performed based on a predetermined compression strength to create irreversible compressed image data.