JP6089738B2 - 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. This is because if the amount of image data is increased, it will take time to download over the Internet, and the display and scrolling speed will slow down. Therefore, the method of thinning out the image to match the standard resolution of the screen (75ppi, 300ppi for printed materials) It is because it has been. Since this operation is performed uniformly for all images so as to reduce the target data amount, there is a problem that it is difficult to read in an image that has many caption characters and requires high image quality.

  FIG. 13 shows a flow of creating a PDF electronic document. Document files created in MS-Word (registered trademark) .doc, PowerPoint (registered trademark) .ppt, Illustrator (registered trademark) .ai, InDesign (registered trademark) .ind, etc. The Adobe Acrobat application shown in FIG. 13 provides two types of creation means. The first method is edited by a document creation application such as MS-office and converted to a graphic screen drawing format such as GDI (Windows), QuickDraw (Apple), etc. (GDI, Windows, QuickDraw, and Apple are registered trademarks). After that, it is converted into a PDF format file by an application called PDF Maker (flow on the left side of FIG. 13) of Acrobat (registered trademark). This method is suitable for creating a PDF file for viewing purposes on a terminal, and has the feature that high-level functions such as hyperlinks can be maintained even in a PDF file, and has the function to reversely convert document files such as original .doc files. It can also be used (supported in the latest version of Acrobat).

  Another method is that after editing with a document creation application such as MS-office is converted to a printer output format represented by PostScript .PS / EPS (registered trademark), Acrobat Distiller (registered trademark) This is a method of conversion into a PDF file by a PDF conversion application called (flow on the right side of FIG. 13). This method is suitable for creating a PDF format file that requires high resolution and high quality such as printed matter, and has a feature that the resolution can be changed in accordance with the capability of the output device. In any PDF format created by either method, the body text can be expressed in three forms: character code, outline (Adobe Illustrator, InDesign only), and bitmap. However, the caption text in the image and the image can be expressed in bitmap format. Limited. Therefore, in order to make the characters clear, it is necessary to increase the resolution to the printing plate making application level. On the other hand, in order to correspond to an electronic book terminal or a tablet terminal having a small processing capacity, it is necessary to reduce the data amount as much as possible. is there.

  As a method for compressing a page description language file such as PDF or PS, a method is proposed in which graphic data arranged is converted into image data, and if the latter is smaller, it is replaced with image data (Patent Literature). 1).

JP 2006-166177 A

  However, the technique described in Patent Document 1 has a problem that it cannot be applied to photographic data, contrary to the idea of PDL (Page Description Language) that quality does not deteriorate even if it is enlarged.

  Therefore, an object of the present invention is to provide an electronic document file compression apparatus capable of reducing the data amount of the entire document file while maintaining the quality of a page requiring high resolution.

  In order to solve the above problems, in the first aspect of the present invention, the data amount of a document file is reduced by changing the resolution of image data pasted in a document file composed of a plurality of pages for each page. An electronic document file compression apparatus that reads a job definition file that defines resolution for each page that constitutes the document file, and that is defined in the job definition file for each page that constitutes the document file. When there is image data having a resolution that exceeds the upper limit resolution set based on the definition resolution, an image resolution conversion unit that performs resolution conversion on the image data so as to have the definition resolution defined in the job definition file Image data converted by the image resolution conversion means and the image resolution conversion Image compression means for compressing both image data whose resolution has not been converted by the means based on a predetermined compression strength, and each page constituting the document file containing the image data compressed by the image compression means A single page conversion unit that performs format conversion on elements other than the image to create single page data, and a single page that corresponds to all pages constituting the document file converted by the single page conversion unit. Data amount calculating means for calculating the total data amount of one page data, and file integration means for integrating single page data corresponding to all pages constituting the document file into a single file, When the total amount of data calculated by the data amount calculation means exceeds a predetermined value, the job definition file creation means, the image resolution conversion The image compression unit and the single page conversion unit perform processing for creating single page data again until the total data amount falls within a predetermined value, and the file integration unit determines that the total data amount is Provided is an electronic document file compression device characterized in that when it falls within a predetermined value, the file integration means performs processing for integration into a single file.

  According to the first aspect of the present invention, a job definition file in which a resolution is defined is created for each page of a document file, and image data that exceeds the resolution defined in the job definition file exists for each page. In this case, resolution conversion is performed on the image data so as to have the resolution defined in the job definition file, and compression such as JPEG compression is performed on both the resolution-converted image and the image data not subjected to resolution conversion. To convert all elements such as characters and figures other than the image data of each page of the document file including the compressed image data into a predetermined format such as PDF format, and create single page data, The total data amount of single page data corresponding to all pages is calculated, and when the total data amount exceeds a predetermined value, the above process is repeated, and the total data amount is calculated. When the amount of data falls within a predetermined value, single page data corresponding to all pages of the document file is integrated into a single file, while maintaining the quality of pages that require high resolution. It is possible to reduce the data amount of the entire document file.

  In the second aspect of the present invention, the job definition file defines a compression strength in addition to the resolution for each page constituting the document file, and the image compression means is configured to perform the predetermined compression. As the strength, each page is compressed using the compression strength defined in the job definition file.

  According to the second aspect of the present invention, the compression strength such as JPEG compression is defined in addition to the resolution for each page of the document file, and the compression strength defined in the job definition file is defined for each page. Since the compression is performed by using the data, it is possible to determine the degree of data amount reduction by the two factors of resolution and compression strength.

  In the third aspect of the present invention, the upper limit resolution is set by multiplying the definition resolution defined in the job definition file by a predetermined coefficient of 1 or more.

  According to the third aspect of the present invention, the definition defined in the job definition file is set as the upper limit resolution by multiplying the definition resolution by a predetermined coefficient of 1 or more for each page of the document file. When there is an image with a boundary resolution slightly higher than the resolution and lower than the upper limit resolution (frequently), processing is not performed on the image having the boundary resolution, so that the resolution conversion is executed. Image quality can be reduced and image quality deterioration due to resolution conversion can be suppressed.

  In the fourth aspect of the present invention, single image data is extracted from each page constituting the document file, and the resolution is set to N (N> 1) for the entire extracted image data or a partial area. ) Create and display resolution-converted image data corresponding to N resolutions that have been changed to a number of values, and specify the resolution corresponding to the resolution-converted image data selected from the displayed resolution-converted image data for each page. It has job definition file creation means for creating the job definition file by defining the resolution.

  According to the fourth aspect of the present invention, single image data is extracted from each page constituting the document file, and the resolution is set to N (N> 1) for the entire extracted image data or a partial area. The resolution conversion image data corresponding to the N resolutions changed to the individual values is created and displayed, and the resolution corresponding to the resolution conversion image data selected from the displayed resolution conversion image data is set to the resolution of each page. Since the job definition file is created by defining as, the optimum resolution can be easily selected while checking the image quality according to the resolution of multiple stages, and the job definition file can be created efficiently. it can.

  In the fifth aspect of the present invention, the job definition file creation means further applies M () to each of the whole or a part of the extracted image data and the created N resolution conversion image data. M> 1) Compressed data such as JPEG compression is performed with the number of compression strengths to create compressed image data corresponding to the number of compression strengths, and the created compressed image data and the data amount of the compressed image data are displayed and displayed. The compression strength corresponding to the compressed image data selected from the compressed image data is defined as the compression strength of each page.

  According to the fifth aspect of the present invention, M (M> 1) compressions are further performed on the whole or a part of the extracted image data and each of the generated N resolution conversion image data. The compressed image data corresponding to the M compression intensities is generated by compression according to the intensity, the generated compressed image data and the data amount of the compressed image data are displayed, and the compressed image selected from the displayed compressed image data Since the compression strength corresponding to the data is defined as the compression strength of each page, it is easy to combine the optimal resolution and compression strength while checking the image quality according to multiple levels of compression strength in addition to the resolution. The job definition file can be created efficiently.

  According to the present invention, it is possible to reduce the data amount of the entire document file while maintaining the quality of a page that requires a high resolution.

It is a hardware block diagram of the compression apparatus of the electronic document file which concerns on one Embodiment of this invention. It is a functional block diagram which shows the structure of the compression apparatus of the electronic document file which concerns on one Embodiment of this invention. It is a flowchart for producing the variation chart required for the compression process of an electronic document file. It is a flowchart which shows the process outline | summary of the compression apparatus of the electronic document file which concerns on one Embodiment of this invention. It is a figure which shows the example which reduces an image by the ratio 1/2 with (alpha) = 2. It is a figure which shows the example which generalizes (alpha) and reduces by ratio 1 / alpha. It is a figure which shows the example expanded by ratio 2 as (alpha) = 2. It is a figure which shows the example which generalizes (alpha) and expands by the ratio (alpha). It is a figure which shows the allocation position of a variation chart. It is a figure which shows the specific example of a variation chart. It is a figure which shows the ratio of the data amount with respect to original image data of each compression image data in the variation chart shown in FIG. It is a figure which shows an example of a job definition file. It is a figure which shows the flow of preparation of a PDF format electronic document.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
<1.1. Device configuration>
FIG. 1 is a hardware configuration diagram of an electronic document file compression apparatus according to an 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 (for example, a hard disk, a flash memory, etc.) 3 for storing programs and data executed by the CPU 1, a key input I / F (interface) 4 such as a keyboard and a mouse, and an external A data input / output I / F (interface) 5 for data communication with a device (data storage medium or the like) 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 job definition file creation means, 20 is an image resolution conversion means, 30 is an image compression means, 40 is a single page conversion means, 50 is a data amount calculation means, 55 is a file integration means, and 60 is a document file. Storage means, 70 is a compressed document file storage means, and 80 is a job definition file storage means.

  The job definition file creation unit 10 extracts the document file stored in the document file storage unit 60 and creates a job definition file for each page of the document file. The image resolution conversion means 20 converts the resolution of the image data so that the resolution defined by the job definition file is obtained. The image compression means 30 performs compression such as JPEG compression on both the image data whose resolution has been converted by the image resolution conversion means 20 and the image data whose resolution has not been converted. The single page conversion unit 40 converts the elements other than the image of each page including the image data compressed by the image compression unit 30 into a format such as the PDF format, and creates single page data. The data amount calculation unit 50 calculates the total data amount of all created single page data. If the calculated total data amount exceeds a predetermined value, the job definition file generation unit 10, image resolution conversion The means 20, the image compression means 30, and the single page conversion means 40 are means for repeatedly performing the process of creating single page data until the total data amount falls within a predetermined value. The file integration unit 55 performs a process of integrating into a single file when the total data amount falls within a predetermined value.

  The document file storage unit 60 is a storage unit that stores a document file that is an electronic document that can be processed by a computer, and is realized by the storage device 3. The document file stored in the document file storage means 60 is an electronic document with an image attached in various formats such as MS-Word.doc, PowerPoint.ppt, Illustrator.ai, and InDesign.ind. Is available. The compressed document file storage unit 70 is a storage unit that stores a compressed document file that is a compressed document file, and is realized by the storage device 3. Although various types of compressed document files can be used, the present embodiment uses the PDF format, which is a general-purpose format. The job definition file storage unit 80 is a storage unit that stores the job definition file created by the job definition file creation unit 10, and is realized by the storage device 3. The job definition file creation means 10, the image resolution conversion means 20, the image compression means 30, the single page conversion means 40, the data amount calculation means 50, and the file integration means 55 are programs that the CPU 1 stores in the storage device 3. It is realized by executing.

  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. A desktop or notebook personal computer including a CPU and a storage device having a calculation speed capable of processing a large-capacity 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 functions as the job definition file creation unit 10, the image resolution conversion unit 20, the image compression unit 30, the single page conversion unit 40, the data amount calculation unit 50, and the file integration unit 55. The function will be realized. The storage device 3 not only functions as the document file storage unit 60, the compressed document file storage unit 70, and the job definition file storage unit 80, but also stores various data necessary for processing as an electronic document file compression unit. To do.

<1.2. Creating a job definition file>
Next, the processing operation of the electronic document file compression apparatus shown in FIGS. 1 and 2 will be described. First, before performing the compression process itself, a job definition file used for the compression process is created. In order to create a job definition file efficiently, it is convenient to create a variation chart for each page in advance (not for pages with no images or pages with similar layouts. You don't have to do that). FIG. 3 is a flowchart showing a variation chart creation process. When the user selects a document file to be compressed via the key input I / F 4, the job definition file creation unit 10 acquires one page from a plurality of pages in the selected document file, The image pasted on the page is displayed on the display unit 6 (step S1).

  The user selects one image as a representative image from a plurality of images displayed in units of pages. Specifically, one of the displayed images is instructed using an input device such as a keyboard or a mouse. The instructed content is transmitted to the job definition file creation means 10 via the key input I / F 4. When the representative image is selected, a trimming frame can be optionally designated (the evaluation target area is cut out for easy evaluation), and the job definition file creation means 10 calculates the resolution of the representative image as the assigned resolution (step S2). ). The allocation resolution is calculated by the job definition file creation means 10 executing a process according to the following [Equation 0].

[Formula 0]
Allocation resolution = Number of pixels / Actual size of allocation

  As shown in [Equation 0], the allocation resolution is calculated by dividing the number of pixels by the actual allocation size. The actual allocation size is a fixed value set in advance for each image pasted on each page, and does not change in calculation of the allocation resolution.

  Next, the job definition file creation means 10 performs reduction processing on the original image data at a ratio of designated resolution / allocation resolution to create reduced image data (step S3). The reduced image data creation process in step S3 will be described with reference to FIGS.

FIG. 5 shows an example in which the specified resolution / assigned resolution = 1/2 (= 1 / α) and the image is reduced at a ratio of 1/2. However, although a specified integer value such as 300 PPI (Pixel Per Inch) is set for the specified resolution, the allocation resolution is a value that is individually specified in the design, so it has a fraction such as 621 PPI, and α is usually a real value. Become. FIG. 5A shows 16 pixels in the original image data, and FIG. 5B shows 4 pixels in the reduced image data by the bilinear method. In the present embodiment, each pixel value of the original image data is expressed as S (i, j, c) (0 ≦ i ≦ Sx−1, 0 ≦ j ≦ Sy−1, c = 0, 1, 2). Each pixel value of the reduced image data is expressed as T (i, j, c) (0 ≦ i ≦ Sx / α−1, 0 ≦ j ≦ Sy / α−1, c = 0, 1, 2). Therefore, the image size (number of pixels) of the original image data is Sx × Sy, and the image size (number of pixels) of the reduced image data is Sx × Sy / α ² . C = 0, 1, and 2 correspond to the three primary colors R (red), G (green), and B (blue), respectively.

  As a method for reducing the original image data, various known techniques such as nearest neighbor, bilinear, and bicubic can be used. In this embodiment, the bicubic method having the best quality is often employed. However, the following will be described based on the bilinear method for the sake of simplicity. In the example of FIG. 5, each pixel value T (i, j, c) of the reduced image data is calculated by the bilinear method according to the following [Equation 1].

[Formula 1]
T (i, j, c) = {S (i, j, c) + S (i + 1, j, c) + S (i, j + 1, c) + S (i + 1, j + 1, c)} / 4

“4” in [Formula 1] indicates α ² in the case of α = 2. In the example of FIG. 5, the four pixel values S (i, j, c), S (i + 1, j, c), S (i, j + 1, c), and S (shown in the upper left of FIG. Using i + 1, j + 1, c), the pixel value T (i, j, c) shown in the upper left corner of FIG. 5B is obtained by the above [Equation 1]. Accordingly, the 16 pixels shown in FIG. 5A are reduced to 4 pixels shown in FIG.

  Since α is generally a real value as described above, FIG. 6 illustrates an example in which α is generalized and reduced by a ratio 1 / α. FIG. 6A shows the pixels in the original image data, and FIG. 6B shows the pixels in the reduced image data. In the example of FIG. 6, the pixel values T (i, j, c) of the reduced image data are calculated by the bilinear method according to the following [Equation 2].

[Formula 2]
T (i, j, c) = Σq _{= 0, α−1} Σk _{= 0, α−1} {S (i + k, j + q, c)} / α ²

In [Expression 2], k is an integer that can take a value of 0 ≦ k ≦ α−1, q is an integer that can take a value of 0 ≦ q ≦ α−1, and Σ _{q = 0, α−1.} Indicates the sum from q = _{0 to α-1,} and Σ _{k = 0, α-1}
Indicates the total from k = 0 to α-1. In the example of FIG. 6, the values S (i, j, c),..., S (i + α-1, j, c),. Using (i, j + α-1, c),..., S (i + α-1, j + α-1, c), the above-described [Equation 2] allows the pixels shown in the upper left corner of FIG. The value T (i, j, c) will be obtained. The number of pixels of the image is reduced by reducing the image in step S3. Next time, when calculating the allocation resolution in step S2, this number of pixels is used.

  Once the reduced image data has been created, the job definition file creation means 10 next performs enlargement processing on the reduced image data at a predetermined ratio α (α> 1) to create image data for assignment (step S4). . The allocation image data creation process in step S4 will be described with reference to FIGS.

  FIG. 7 shows an example of enlargement at a ratio of 2 with α = 2. FIG. 7A shows four pixels in the original image data, and FIG. 7B shows nine pixels in the allocation image data. In the present embodiment, each pixel value of the image data for assignment is expressed as R (i, j, c) (0 ≦ i ≦ Sx−1, 0 ≦ j ≦ Sy−1, c = 0, 1, 2). To do. Therefore, the image size (number of pixels) of the allocation image data is Sx × Sy, similar to the image size (number of pixels) of the original image data. C = 0, 1, and 2 correspond to the three primary colors R (red), G (green), and B (blue), respectively.

  As a technique for enlarging the reduced image data, various known techniques such as nearest neighbor, bilinear, and bicubic can be used. Of course, the same technique as that used for the reduction is used. In the present embodiment, since the bicubic method is used at the time of reduction, the bicubic method is often used also at the time of enlargement, but the following will be described based on the bilinear method for the sake of simplicity. According to the bilinear method, in the example of FIG. 7, each pixel value R (i, j, c) of the image data for allocation is calculated according to the following [Equation 3].

[Formula 3]
R (i, j, c) = T (i, j, c)
R (i + 1, j, c) = {T (i, j, c) + T (i + 1, j, c)} / 2
R (i + 2, j, c) = T (i + 1, j, c)
R (i, j + 1, c) = {T (i, j, c) + T (i, j + 1, c)} / 2
R (i + 1, j + 1, c) = {T (i, j, c) + T (i + 1, j, c) + T (i, j + 1, c) + T (i + 1, j + 1, c)} / 4
R (i + 2, j + 1, c) = {T (i + 1, j, c) + T (i + 1, j + 1, c)} / 2
R (i, j + 2, c) = T (i, j + 1, c)
R (i + 1, j + 2, c) = {T (i, j + 1, c) + T (i + 1, j + 1, c)} / 2
R (i + 2, j + 2, c) = T (i + 1, j + 1, c)

  In the example of FIG. 7, the values T (i, j, c), T (i + 1, j, c), T (i, j + 1, c), T (i + 1) of the four pixels shown in the upper left of FIG. , J + 1, c), and using the above [Equation 3], the nine pixel values R (i, j, c), R (i + 1, j, c), R ( i + 2, j, c), R (i, j + 1, c), R (i + 1, j + 1, c), R (i + 2, j + 1, c), R (i, j + 2, c), R (i + 1, j + 2, c) ), R (i + 2, j + 2, c).

  Since α is generally a real value as described above, FIG. 8 illustrates an example in which α is generalized and enlarged by the ratio α. FIG. 8A shows pixels in the reduced image data, and FIG. 8B shows pixels in the allocation image data. In the example of FIG. 8, each pixel value R (i + k, j + q, c) of the reduced image data is calculated by the bilinear method according to the following [Equation 4].

[Formula 4]
R (i + k, j + q, c) = [(α−q) · {(α−k) · T (i, j, c) + k · T (i + 1, j, c)} + q · {(α−k) T (i, j + 1, c) + kT (i + 1, j + 1, c)}] / α ²

In [Formula 4], as in [Formula 2], k is an integer that can take a value of 0 ≦ k ≦ α−1, and q is an integer that can take a value of 0 ≦ q ≦ α−1. In the example of FIG. 8, the values T (i, j, c), T (i + 1, j, c), T (i, j + 1, c), T ( i + 1, j + 1, c), and using the above [Equation 4], the pixel values R (i, j, c),..., R (i + α, j, c) shown in the upper left of FIG. , ..., S (i + k, j + q, c), ..., S (i, j + α, c), ..., S (i + α, j + α, c).

  Once the allocation image data has been created, the job definition file creation means 10 then determines whether or not the processing has been completed for all the designated resolutions n (n = 1, 2,..., N) ( Step S5). Specifically, the determination is made based on whether or not n = N.

  If n = N is not reached, n ← n + 1 is incremented, and the designated resolution is changed to one corresponding to the new n (step S6). After the designated resolution is changed, the process returns to step S2, but as described above, in step S2, the process according to [Equation 1] is executed using the number of pixels of the reduced image data reduced in step S3. To calculate the assigned resolution.

  After the processes of steps S2 to S6 are repeated n times and finished for all the designated resolutions, the job definition file creation means 10 compresses the representative image data and the image data for allocation of each designated resolution n (steps). S7). Therefore, N + 1 pieces of image data are compressed. Various known compression methods can be used as the compression method of the image data. In this embodiment, the JPEG method is used. As the compression strength, a preset compression strength is used.

  Next, the job definition file creation means 10 performs a process of expanding the image data compressed in step S7 (step S8). That is, N + 1 compressed image data obtained by compressing the representative image data and the image data for allocation with each designated resolution n is expanded. Naturally, the decompression is performed in the same manner as the compressed method. Therefore, in this embodiment, decompression is performed using the JPEG method.

  Next, the job definition file creation means 10 determines whether or not the processing has been completed for all the compression strengths m (m = 1, 2,..., M) (step S9). Specifically, the determination is made based on whether m = M has been reached.

  If m = M has not been reached, m is incremented as m ← m + 1, and the designated compression strength is changed to that corresponding to the new m (step S10). After changing the compression strength, the compression of the image data in step S7 and the expansion of the image data in step S8 are repeatedly performed according to the compression strength after the change.

  After the processes of steps S7 to S10 are repeated m times, and when all the compression strengths are completed, the job definition file creation unit 10 assigns all the decompressed images (step S11). Therefore, (N + 1) × M expanded images are allocated. Allocation is performed using one of the vertical and horizontal axes as the compression strength and the other axis as the designated resolution. As a result, a variation chart of the target page is obtained. Similarly, the process of FIG. 3 is executed for the number of pages in the document file, and a variation chart of all pages in the document file is obtained.

  FIG. 9 is a diagram showing the allocation position of the created variation chart. As shown in FIG. 9, the variation chart is configured in units of pages. 9A shows a variation chart for page 1 and FIG. 9B shows a variation chart for page P. FIG. As shown in FIGS. 9A and 9B, the variation chart of each page is allocated with the expanded image data in which the designated resolution and the compression strength are changed with the designated resolution on the horizontal axis and the compression strength on the vertical axis. Yes.

  FIG. 10 is a diagram showing a specific example of a variation chart on a certain page. FIG. 10 shows the case where the number of designated resolutions N = 4 and the number of compression strengths M = 5, and (N + 1) × M = 25 decompressed images are displayed in total. As is apparent from FIG. 10, as a tendency, the stretched image gradually becomes unclear from the upper left toward the lower right.

  FIG. 11 is a diagram showing the ratio of the data amount of each compressed image data to the original image data in the variation chart shown in FIG. As shown in FIG. 11, it can be seen that the data amount decreases as the specified resolution decreases, and the data amount decreases as the compression strength increases. After creating the variation chart, the job definition file creation means 10 displays the variation chart shown in FIG. 10 and the variation chart shown in FIG. 11 on the display unit 6 to prompt the user to select. There are various methods for setting the compression strength. In this embodiment, as shown in FIGS. 10 and 11, the compression strength is set in five stages of the highest image quality, high image quality, medium image quality, low image quality, and lowest image quality. doing. In the case of the highest image quality, compression is not performed because it is uncompressed. The higher the compression strength, the lower the image quality. In the variation charts of FIGS. 10 and 11, when the representative image (original resolution) / medium image quality surrounded by a thick frame is compared with the designated resolution 4 / high image quality, the data amount of the representative image / medium image quality is smaller. It can be seen that the image is clear. In this case, it is preferable to select a representative image / medium image quality (specifically, the instruction is to maintain only the original resolution and not perform resolution conversion, and only perform JPEG compression with medium image quality). In this way, the user compares the two variation charts and selects one frame from the variation charts. The job definition file creation unit 10 records the designated resolution and compression strength corresponding to the selected frame in the job definition file as the definition values (definition resolution and compression strength) of the page.

  Similarly, a variation chart is displayed for each page, and a definition value (definition resolution and compression strength) is recorded based on selection of a designated resolution and compression strength, thereby completing a job definition file. FIG. 12 is a diagram illustrating an example of a job definition file created by the job definition file creation unit 10. As shown in FIG. 12, in the job definition file, a set of definition resolution and compression strength is recorded for each page. The job definition file creation unit 10 stores the created job definition file in the job definition file storage unit 80. Also, an upper limit resolution is defined based on the definition resolution. Various rules can be used for defining the upper limit resolution based on the definition resolution. In this embodiment, a value obtained by multiplying the definition resolution by one or more coefficients is defined. In the example described later, this coefficient is set to 1.5.

<1.3. Compression of electronic document files>
When the job definition file is created and ready in the job definition file storage unit 80, the electronic document file is compressed. FIG. 4 is a flowchart showing compression processing of an electronic document file. In the electronic document file compression apparatus, first, the image resolution conversion means 20 reads a job definition file from the job definition file storage means 80 and then pages p (p = 1, 2,..., P from the job definition file. : The definition value (definition resolution and compression strength) of the initial value p = 1) is read (step S21).

  Next, the image resolution conversion unit 20 reads the document file from the document file storage unit 60 and reads the image data pasted on the page p (step S22). Subsequently, the image resolution conversion means 20 compares the upper limit resolution set based on the definition resolution read from the job definition file in step S21 and the resolution of the image data read in step S22 (step S23). Here, the upper limit resolution is not the definition resolution itself read from the job definition file, but a value multiplied by 1.5 and used as the upper limit resolution referred to in step S23. The reason is that if the resolution of the read image data has a fraction such as 301 PPI and the definition resolution is 300 PPI, the process proceeds to step S24 and resolution conversion processing is performed. 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 image data is within the boundary range of 301 to 450 PPI, the value of the upper limit resolution is made slightly larger than the definition resolution so as not to proceed to step S24. If it exceeds 450 PPI, it is reduced to 300 PPI in step S24, and the definition resolution in this case uses the definition resolution itself. The resolution of the image data is calculated by recognizing the number of pixels of the image read by the image resolution conversion means 20 and dividing the number of pixels by a preset actual size.

  As a result of the comparison in step S23, if the resolution of the read image is less than or equal to the upper limit resolution, resolution conversion is not performed and the process proceeds to step S25. This is because when the resolution of the read image is lower than the upper limit resolution, it is not necessary to lower the resolution any more. On the other hand, if the result of comparison in step S23 is that the resolution of the read image is greater than the upper limit resolution, processing for converting the resolution is performed (step S24). Specifically, a process of reducing the image at a ratio of (definition resolution) / (resolution of the read image) is performed. Thereby, reduced image data with a reduced number of pixels is obtained.

  Next, the image compression means 30 compresses the image (step S25). In step S25, both the image data whose resolution has been converted by the image resolution conversion means 20 and the image data that has not been converted are compressed. The compression strength is set at any one of the five levels set for each page of the job definition file. When a plurality of images are pasted on one page, the images are compressed with a common compression strength. Various known methods can be used as the compression method, but it is necessary to use the method used when creating the job definition file. Therefore, in this embodiment, the JPEG method is used. The processes in steps S22 to S25 are performed on all image data corresponding to the page p read in step S21.

  After all the image data on the page p is compressed, the single page conversion means 40 creates page data (step S26). As the page data format, various known formats can be used, but in this embodiment, the PDF format is used. Specifically, the compressed image data is pasted into a document file, and the pasted page document is converted into PDF page data. This process is performed using an algorithm similar to a known PDF conversion application such as Acrobat (registered trademark).

  Subsequently, the data amount calculation unit 50 determines whether or not the processing up to the creation of page data has been completed for all pages in the document file (step S27). Specifically, in the case of a document file having P pages, the determination is made based on whether or not p = P. When the processing has not been completed for all pages (when p <P), the data amount calculation unit 50 changes the processing target to the next page (step S28). Specifically, p is incremented as p ← p + 1, and the process from step S21 is performed on the new page p.

  If it is determined in step S27 that processing has been performed for all pages in the document file, the data amount calculation unit 50 calculates the total data amount of all pages (step S29). Specifically, the calculation is performed by obtaining the sum of the data amount of the page data including the compressed image.

  Then, the data amount calculation unit 50 compares the data amount with the upper limit value set in advance (step S30). As a result of the comparison, when the total data amount calculated in step S29 exceeds the upper limit value, the data amount calculation unit 50 corrects the job definition file (step S31). More specifically, the definition resolution and compression strength of each page are changed to one level lower. After setting p = 1, the process returns to step S21, and the document file is processed again from the first page.

  As a result of the comparison in step S30, when the total data amount is equal to or less than the upper limit value, the file integration unit 55 integrates all pages into one compressed document file (step S32). This processing is performed using an algorithm similar to a known PDF conversion application such as Acrobat.

<2. Modified example>
As mentioned above, although it limited about the suitable embodiment of the present invention, the present invention is not limited to the above-mentioned embodiment, and various modifications are possible. For example, in the above embodiment, the resolution and the compression strength are defined for each page constituting the document file in the job definition file, but the JPEG compression strength is not defined, and only the resolution is defined. Also good.

  In the above embodiment, the case where PDF is used as a document file that is an electronic document has been described as an example. However, an electronic document to which an image to be compressed in a predetermined pixel block unit is attached is related to the document format. It is possible to respond.

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 section 10 ... Job definition file creation means 20 ... Image resolution conversion means 30 ... Image compression means 40 ... Single page conversion means 50 ... Data amount calculation means 55 ... File integration means 60 ... Document file storage means 70 ... Compressed document file storage means 80 ... Job definition file storage means

Claims (6)

An electronic document file compression apparatus that reduces the data amount of a document file by changing the resolution of image data pasted in a document file composed of a plurality of pages for each page,
A job definition file in which resolution is defined for each page constituting the document file is read, and an upper limit resolution set based on the definition resolution defined in the job definition file is set for each page constituting the document file. Image resolution conversion means for performing resolution conversion so that the image data having the resolution exceeding the definition resolution defined in the job definition file is applied to the image data;
Image compression means for compressing both the image data converted by the image resolution conversion means and the image data not converted by the image resolution conversion means based on a predetermined compression strength;
Single page conversion means for performing format conversion on elements other than the images of each page constituting the document file including the image data compressed by the image compression means, and creating single page data;
A data amount calculating means for calculating a total data amount of single page data corresponding to all pages constituting the document file converted by the single page converting means;
File integration means for integrating single page data corresponding to all the pages constituting the document file into a single file,
When the total data amount calculated by the data amount calculation unit exceeds a predetermined value, the job definition file creation unit, the image resolution conversion unit, the image compression unit, and the single page conversion unit The process of creating single page data again is performed until the data amount falls within a predetermined value. When the total data amount falls within the predetermined value, the file integration unit uses the file integration unit to An apparatus for compressing an electronic document file, characterized in that processing for integration into one file is performed. In claim 1,
The job definition file defines the compression strength in addition to the resolution for each page constituting the document file.
The image compression unit compresses each page using the compression strength defined in the job definition file as the predetermined compression strength. . In claim 1 or claim 2,
The electronic document file compression apparatus, wherein the upper limit resolution is set by multiplying a definition resolution defined in the job definition file by a predetermined coefficient of 1 or more. In any one of Claims 1-3,
A single image data is extracted from each page constituting the document file, and the resolution is changed to N (N> 1) values for the whole or a part of the extracted image data. The job definition file is generated by generating and displaying resolution-converted image data corresponding to the resolution of the image, and defining the resolution corresponding to the resolution-converted image data selected from the displayed resolution-converted image data as the resolution of each page. An electronic document file compression apparatus comprising job definition file creation means for creating a file. In claim 4,
The job definition file creation means further includes M (M> 1) compression intensities for the whole or a part of the extracted image data and each of the created N resolution conversion image data. To generate compressed image data corresponding to M compression intensities, display the generated compressed image data and the data amount of the compressed image data, and select compressed image data from the displayed compressed image data The electronic document file compression apparatus is characterized in that the compression strength corresponding to is defined as the compression strength of each page.   A program for causing a computer to function as the electronic document file compression device according to any one of claims 1 to 5.

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