JP5947384B2 - Image compression apparatus, operation control method thereof, and operation program thereof - Google Patents

Description

  The present invention relates to an image compression apparatus, an operation control method thereof, and an operation program thereof.

  By sending electronic comics to mobile phones such as smartphones, it has become possible to display comics on the display screen of mobile phones. Since the amount of data is large when an electronic comic is transmitted without being compressed, it is often compressed so that the total data amount of the electronic comic is less than a predetermined data amount.

  When compressing image data, encoding is performed while continuing to input the image data (Patent Document 1), so that the image size of each page is constant in the image data in which each page is divided into a plurality of blocks. There are those that do (Patent Document 2), those that compress images at a compression rate set by the user (Patent Document 3), and those that prevent a reduction in the speed of continuous recording (Patent Document 4).

JP 2004-312180 A JP 2004-159069 A JP-A-6-326872 JP-A-6-654309

  When compressing digitized comics, the density of comics is not uniform across all pages, so if all pages are compressed with a uniform compression ratio, differences in image quality may be noticeable from page to page.

  An object of the present invention is to make the image quality of each page of an image group such as a comic book, a photo book, and a photo book (photo album) equal.

  The compression apparatus according to the present invention includes a first compression rate at which each page image of an image group composed of a plurality of page images has an image quality equal to or higher than a predetermined minimum image quality. The first compression means for performing the first compression processing using the initial compression ratio between the second compression ratio in which the data amount of the compressed image group is equal to or less than the predetermined overall target data amount , And the second compression processing is performed in order of decreasing data amount after compression of the page images constituting the image group compressed by the first compression means, and the nth (n is an integer of 1 or more) th The page image target data amount for the page image is [(total target data amount) − {total data amount when the second compression processing is performed for the (n−1) th page images}] × (First compression processing Data amount of the n-th page image obtained in step) / [(data amount of the entire image group obtained in the first compression processing) − {(n−1) obtained in the first compression processing. 2) a second compression means for performing the second compression processing so that the total data amount of the first page image}.

  The present invention also provides an operation control method suitable for an image compression apparatus. In other words, in this method, the first compression means has the image quality of the page group of the image group composed of a plurality of page images, and the compressed page image has an image quality higher than the predetermined minimum image quality. The first compression processing is performed using an initial compression ratio between the first compression ratio and a second compression ratio at which the data amount of the compressed image group is equal to or less than a predetermined overall target data amount. , The second compression means performs the second compression processing in order from the smallest data amount after compression of the page images constituting the image group compressed by the first compression means, and the nth page The page image target data amount for the image is [(total target data amount) − {total data amount when the second compression processing is performed for the (n−1) th page images}] × (first Obtained in 1 compression process Data amount of the n-th page image) / [(data amount of the entire image group obtained in the first compression processing) − {until the (n−1) -th obtained in the first compression processing] The second compression process is performed so that the total data amount of the page image} is obtained.

  The present invention also provides a computer-readable program for controlling the operation of the image compression apparatus. A recording medium storing such a program may be provided.

  According to the present invention, each of the page images constituting the image group has the first compression rate at which the image quality exceeds the minimum image quality, and the second compression at which the data amount of the image group after compression is equal to or less than the total target data amount. The first compression processing is performed using an initial compression ratio between the ratios. For a plurality of page images constituting the image group on which the first compression processing has been performed, the second compression processing is performed in ascending order of the data amount after compression of the first compression processing. In the second compression processing, the data amount of the n-th (n is an integer equal to or greater than 1) -th page image is equal to (second target data amount)-{second (n-1) -th page image. Total amount of data when compression processing is performed}] × (data amount of nth page image obtained in first compression processing) / [(total image group obtained in first compression processing) (Data amount)-{total data amount of the (n-1) th page images obtained in the first compression processing}.

  According to the present invention, since the second compression process is performed according to the ratio between the data amount of the entire image group after the first compression process and the total target data amount, the first compression process and the second compression process are performed. The data amount of the subsequent image group becomes the total target data amount, and the image quality of all the page images constituting the image group becomes relatively uniform.

  For example, the second compression means may increase the target data amount of the page image by a predetermined ratio when the second compression processing that becomes the page image target data amount cannot be performed.

  When a plurality of frames are assigned to the page image, the second compression means, for example, the m-th image in order of decreasing (data amount of frame / area of frame) after the first compression processing. The frame image target data amount for the frame image is [(page image target data amount) − {total data amount of the frame image when the second compression processing is performed for the (m−1) th frame images. }] × (data amount of the m-th frame image data obtained in the first compression processing) / [(data amount of the page image obtained in the first compression processing) − {in the first compression processing The second compression process may be performed for each frame so that the total data amount of the obtained (m−1) th frame images}.

  For example, the second compression unit may perform the second compression process at the same compression rate for the spread page image in response to the frame being allocated over the spread page image.

  The second compression means is assigned to the first page image in response to the fact that frames are assigned over the spread page image composed of the first page image and the second page image in succession. The second compression processing may be performed by regarding the first frame portion and the second frame portion allocated to the second page image as separate frames.

  The second compression means is assigned to the first page image in response to the fact that frames are assigned over the spread page image composed of the first page image and the second page image in succession. The second compression process may be performed so that the compression rate of the first frame portion and the compression rate of the second frame portion assigned to the second page image are the same.

It is a block diagram which shows the electrical structure of a comic image compression apparatus. It is an example of the page image which comprises a comic image. It is a flowchart which shows the process sequence of a comic image compression apparatus. It is an example of the page image which comprises a comic image. It is an example of the page image which comprises a comic image. It is an example of the page image which comprises a comic image. It is an example of the page image which comprises a comic image. It is an example of the page image which comprises a comic image. It is a flowchart which shows the process sequence of a comic image compression apparatus. It is a flowchart which shows the process sequence of a comic image compression apparatus. It is an example of a page image. It is an example of a frame table. It is an example of a frame image. It is an example of a frame image. It is an example of a frame image. It is an example of a page image.

  FIG. 1 shows an embodiment of the present invention and is a block diagram showing an electrical configuration of a comic image compression apparatus 1.

  The overall operation of the comic image compression apparatus 1 is controlled by the CPU 2.

  The comic image compression apparatus 1 includes a communication interface 3 for connecting to a network such as the Internet, a memory for storing data 4, a display device 5 for displaying comic images, and an input device 6 such as a keyboard. The comic image compression apparatus 1 also includes a hard disk 8, a hard disk drive 7 that accesses the hard disk 8, and a CD-ROM (compact disk-read only memory) drive 9. When a CD-ROM 10 storing a program for controlling operations described later is read by the CD-ROM drive 9, the read program is installed in the comic image compression apparatus 1. The program may be recorded on a recording medium other than the CD-ROM 10, and may be read from such a recording medium and installed in the comic image compression apparatus 1. Alternatively, the program may be transmitted to the comic image compression apparatus 1 via the Internet or the like, and the program received via the communication interface 3 may be installed in the comic image compression apparatus 1. The comic image compression apparatus 1 can be configured using a computer.

  FIG. 2 shows a comic image composed of 10 pages of page images.

  The comic image is composed of ten page images 31 to 40 from the first page image 31 to the tenth page image 40. Of course, the comic image may be composed of page images less than 10 page images, or may be composed of more page images than 10 page images.

  It is assumed that the data amount of each page image from the first page image 31 to the tenth page image 40 is 10 MB. Of course, the data amount may be different for each page image. The total data amount of comic images is 100 MB. In this embodiment, the image quality of each page image from the first page image 31 to the tenth page image 40 is made as uniform as possible, and the total data amount of the comic images is the target data amount (total target data amount). The comic image is compressed so as to be 20 MB.

  FIG. 3 is a flowchart showing the processing procedure of the comic image compression apparatus 1.

  In this embodiment, JPEG (Joint Photographic Experts Group) is used for compression of the comic image. In JPEG, an image is divided into blocks of 8 pixels × 8 pixels, and converted from the spatial domain to the frequency domain using discrete cosine transform in units of blocks. The converted data is subjected to entropy coding using Huffman codes after the amount of data is reduced by quantization. A parameter used in quantization is called a Q value, and the amount of data after compression changes depending on the value of the Q value.

  First, in this embodiment, as shown in FIG. 2, the first Q value is such that the image quality after compression of each of the plurality of page images 31 to 40 is equal to or higher than a predetermined minimum image quality. (First compression rate) and a second Q value (second compression rate) at which the total data amount of the compressed comic image is equal to or less than a predetermined overall target data amount (for example, 20 MB) , The initial Q value (initial compression rate) is determined. Using such initial Q value, the page images of all the page images 31 to 40 constituting the comic image are compressed (first compression process) (step 21).

  FIG. 4 shows the comic image after the first compression processing.

  As a result of the first compression processing, the data amount of the first page image 31 and the data amount of the third page image 33 are both 0.5 MB, the data amount of the second page image 32 is 1 MB, It is assumed that the data amount of the page image 40 is 2 MB. Other page images are also smaller than the data amount before the first compression processing. The amount of data after the first compression processing is different for each page image because the density of the cartoon is different for each page image. A fine page image has a larger amount of data after the first compression process than a non-fine page image.

  It is assumed that the entire data amount of the comic image is 10 MB as a result of the first compression processing. This total data amount of 10 MB is smaller than the total target data amount of 20 MB.

  When the first compression process is performed, the page images 31 to 40 are rearranged in order of decreasing data amount after the first compression process (step 22 in FIG. 3). Rearrangement is performed so that a page image with a small amount of data after the first compression processing is preferentially subjected to second compression processing described later.

  FIG. 5 shows the rearranged page images 31-40.

  In FIG. 5, page images are arranged from the left side in ascending order of data amount after the first compression processing. Page images with the same amount of data after the first compression processing are arranged so that the page image of the previous page is on the left side (first), but is arranged so that the page image of the subsequent page is on the left side. It may be done.

  In FIG. 5, the first page image 31 with a data amount of 0.5 MB is arranged at the very beginning (leftmost), and then the third page image 33 with a data amount of 0.5 MB is arranged. Thirdly, the second page image 32 having a data amount of 1 MB is arranged. The fourth and subsequent page images (not shown) are also arranged in ascending order of data amount after the first compression processing. Finally, the 10th page image 40 having a data amount of 2 MB is arranged.

  When the page images 31 to 40 are rearranged, the nth (n is an integer of 1 or more) page image is compressed so that the data amount (page target data amount) based on the arithmetic expression of Equation 1 is obtained. (Second compression process) (Step 23 in FIG. 3).

  [(Total target data amount) − {total data amount when the second compression processing is performed for the (n−1) th page images}} × (nth obtained in the first compression processing) Data amount of the first page image) / [(data amount of the entire comic image obtained in the first compression process) − {of the (n−1) th page images obtained in the first compression process Total amount of data} ... Equation 1

  FIG. 6 shows a state in which the first page image 31 is subjected to the second compression processing according to Equation 1.

  Since the total target data amount is 20 MB and the first page image 31 is n = 1 in the equation 1, the second compression processing is performed on the {((n-1)) th page images in the equation 1. The total amount of data at the time of the image processing} and {the total amount of data of the (n-1) th page images obtained in the first compression processing} are both 0. Accordingly, the first page image 31 is assigned a Q value such that {(20 MB−0 MB) × (0.5 MB)} / {(10 MB) − (0 MB)} = 1 MB. Processing is performed. By the second compression process, the data amount of the first page image subjected to the first compression process is doubled.

  If the Q value is specified so that the amount of data obtained based on Equation 1 is specified and the second compression processing is performed, whether or not the amount of data obtained based on Equation 1 is actually compressed is tried. I have no idea. For this reason, the second compression process may be performed such that the data amount matches the data amount obtained based on Equation 1, but it may not. For this purpose, it is confirmed whether or not the second compression processing has been performed so that the data amount coincides with the data amount obtained based on Equation 1 (step 24). In such second compression processing, if the data amount does not coincide with the data amount obtained based on Equation 1 (NO in step 24), the data amount obtained based on Equation 1 is set to a predetermined value. The nth page image is compressed so that the data amount is close to the data amount multiplied by the ratio (for example, 1.1) (step 25).

  The processing of step 23 and step 24 is performed for all page images (the processing of step 25 is also performed if necessary) (step 26). If the processing in step 23 and the like has not been completed for all page images, n is incremented (step 27), and the processing from step 23 is repeated again.

  FIG. 7 shows a state in which the second page image 33 is subjected to the second compression processing according to Equation 1.

  Since the total target data amount is 20 MB and the second page image 33 is n = 2 in Equation 1, {(20 MB-1 MB) × (0.5 MB)} / {(10 MB) − (0.5 MB) } = 1 MB is designated, and the second compression process is performed.

  Similar processing is repeated for the third and subsequent page images. The image quality of the page image after the second compression processing is relatively uniform. Moreover, the data amount of the entire comic image after the second compression processing is close to the target data amount.

  FIG. 8 is an example of page images 31 to 40 rearranged after the first compression processing, and corresponds to FIG.

  As described above, when the first compression processing is performed, the page images 31 to 40 are rearranged in ascending order of the amount of data after compression. However, in the comic image, a frame may be formed across the two-page spread image. For two-page spread images on which such frames are formed, rearrangement is defined so as to be continuous.

  In FIG. 5, the data amount of both the first page image 31 and the third page image 33 after the first compression processing is 0.5 MB, and the data amount of the second page image 32 after the first compression processing is 1 MB. As a result, the first page image 31, the third page image 33, and the second page image 32 are rearranged in order of decreasing data amount. In FIG. Since the frame is formed over the page image 32, the first page image 31 and the second page image are formed even though the data amount of the second page image 32 is smaller than the data amount of the third page image 33. 32 is continuous.

  As described above, the second compression processing described above may be performed by rearranging the page images in which the frames are formed over the spread. Furthermore, when a frame is allocated over spread page images, these spread page images may be compressed with the same Q value (compression ratio). Data indicating whether or not a frame is formed over the spread page is stored in advance in the header of the file representing the cartoon image, and the frame is formed on the spread page by referring to the data. Needless to say.

  9 to 15 show other embodiments.

  In this embodiment, the above-described compression process is performed for each frame included in the page image.

  As described above (see FIG. 4), the first compression processing is performed with the initial Q value for all page images constituting the comic image (step 51).

  In each page image of all page images subjected to the first compression processing, for each frame included in the page image, the frame coordinates, the area of the frame, and the data amount of the frame after the first compression processing are stored. (Step 52).

  FIG. 11 is an example of the first page image 31 on which the first compression processing has been performed.

  As described above, the data amount of the first page image 31 subjected to the first compression processing is 0.5 MB.

  The first page image 31 includes six frames from the first frame 71 to the sixth frame 76. Data amount of first frame 71, data amount of second frame 72, data amount of third frame 73, data amount of fourth frame 74, data of fifth frame 75 after the first compression processing The amount and the data amount of the sixth frame 76 are 0.5 MB, 0.07 MB, 0.12 MB, 0.02 MB, 0.11 MB, and 0.08 MB, respectively.

  FIG. 12 is an example of a frame table for the first page image 31. A frame table is similarly formed for the page images constituting the comic image other than the first page image 31.

  In the frame table, columns of frame number, coordinates, area, and data amount are formed. The frame number identifies a frame included in the page image. Frame numbers 1, 2, 3, 4, 5, and 6 are respectively the first frame 71, the second frame 72, the third frame 73, the fourth frame 74, the fifth frame 75, and the sixth frame. It corresponds to frame 76. The coordinates indicate the position of each frame in the page image. Since the frames 71 to 76 constituting the first page image 31 are quadrangles, the positions of the frames 71 to 76 are specified by representing the vertices of the quadrangles with coordinates. For example, the upper left (upper right) of the first page image 31 is the origin. The area is the area of each frame. The data amount is the data amount of each frame on which the first compression processing has been performed. These coordinates, area, and data amount are stored in the frame table corresponding to the frame number. By storing the frame table in the memory 4 of the comic image compression apparatus 1, the coordinates and the like are stored in the comic image compression apparatus 1 for each frame.

  Subsequently, the frame images constituting the page image subjected to the first compression processing are rearranged in order of increasing (data amount of frame / area of frame) (step 53 in FIG. 9).

  FIG. 13 shows an example of the frame images rearranged in ascending order of (frame data amount / frame area).

  In the example shown in FIG. 5, the page images are rearranged in the order of the data amount of the page image after the first compression processing. In this embodiment, the frame images are represented by (frame data amount / frame area). ) In ascending order. This is because the second compression process is preferentially performed for frames with a small amount of data per unit area.

  In FIG. 13, the second frame 72, the fourth frame 74, the sixth frame 76, the fifth frame 75, the third frame 73, and the first frame are in order of increasing (data amount of frame / area of frame). One frame 71 is arranged.

  When the frame images 71 to 76 are rearranged, the mth ((frame image target data amount)) becomes the data amount (the frame image target data amount) based on the arithmetic expression of Equation 2 in the order of decreasing (frame data amount / frame area). The m-th frame image is compressed (second compression processing) (step 54 in FIG. 9).

  [(Page image target data amount) − {total amount of frame image data when the second compression processing is performed for the (m−1) th frame images}] × (obtained in the first compression processing) Data amount of m-th frame image obtained) / [(data amount of page image obtained in first compression processing) − {(m−1) -th obtained in first compression processing) Total data amount of frame image} ... Equation 2

  FIG. 14 shows a state in which the first frame image 72 is subjected to the second compression processing according to Equation 2.

  The page image target data amount is 1 MB as can be seen from FIG. Since the first frame image 72 is m = 1 in Equation 2, in Equation 2, {the frame image when the second compression processing is performed on the (m−1) th frame images. The total data amount} and the total data amount of the (m−1) -th frame images obtained in the first compression processing are both 0. Therefore, the first frame image 72 is subjected to the second compression process with the Q value designated as [(1 MB−0 MB) × (0.07 MB) / (0.5 MB) = 0.14 MB]. By the second compression process, the data amount of the first frame image subjected to the first compression process is doubled.

  If the Q value is specified so that the amount of data is obtained based on Equation 2 and the second compression process is performed, is the amount of data obtained based on Equation 2 as in Equation 1? I don't know if I don't actually compress it. For this reason, the second compression process may be performed such that the data amount matches the data amount obtained based on Equation 2, but it may not be possible. For this purpose, it is confirmed whether or not the second compression processing has been performed so that the data amount matches the data amount obtained based on Equation 2 (step 55). In such a second compression process, when the data amount does not coincide with the data amount obtained based on Equation 2 (NO in Step 55), as described above, based on Equation 2. The m-th frame image is compressed so as to obtain a data amount in the vicinity of the data amount obtained by multiplying the obtained data amount by a predetermined ratio (eg, 1.1) (step 56).

  The processing of step 54 and step 55 is performed for all the frame images (the processing of step 56 is also performed if necessary) (step 57). If the processing in step 54 and the like has not been completed for all the frame images, m is incremented (step 58), and the processing from step 54 is repeated again.

  FIG. 15 shows a state in which the second frame image 74 is subjected to the second compression processing according to Equation 2.

  Since the target data amount of the page image is 1 MB and the second frame image 74 is m = 2 in Equation 2, {(1 MB−0.14 MB) × (0.02 MB)} / {(0.5 MB) − A Q value such that (0.07 MB)} = 0.04 MB is designated, and the second compression processing is performed.

  Similar processing is repeated for the third and subsequent page images. The image quality of the frame image after the second compression processing is relatively uniform within the page image.

  When the above-described compression processing for the frame image for the nth page image is completed, it is confirmed whether the processing has been completed for all page images (step 59 in FIG. 10). If not completed (NO in step 59 in FIG. 10), n is incremented (step 60 in FIG. 10), and the processing from step 52 in FIG. 9 is repeated for the next page image.

  FIG. 16 is an example of a page image showing a state in which a frame is formed over a spread page.

  In FIG. 16, the right side is the first page image 101 and the left side is the second page image 102. In the first page image 101, frames 81 to 85 are formed, and in the second page image 102, frames 91 to 95 are formed. Further, a frame 90 is formed across the first page image 101 and the second page image 102.

  In such a case, among the frames 90, the frame portion 90A included in the first page image 101 and the frame portion 90B included in the second page image 102 are regarded as separate frames, and the above-described processing is performed. You may make it perform. Further, the Q value of the frame portion 90A and the Q value of the frame portion 90B may be the same.

  Further, the second compression processing is performed for each frame image so that all the page images constituting the comic image are rearranged for each frame image, and the data amount after the second compression processing becomes the total target data amount. You may be made to be.

  In the above-described embodiments, comic images have been described. Needless to say, the present invention can be applied not only to comic images but also to image groups such as photo books and photo books (photo albums) composed of a plurality of page images. Nor.

1 cartoon image compression device 2 CPU
31-40, 101, 102 page images
71-76, 81-85, 90-95 frames

Claims (8)

Each page image of an image group composed of a plurality of page images is divided into a first compression rate at which each page image after compression has an image quality higher than a predetermined minimum image quality, and A first compression means for performing a first compression process using an initial compression ratio between a second compression ratio at which the data amount is equal to or less than a predetermined overall target data amount, and the first compression The second compression processing is performed in ascending order of the data amount after compression of the page images constituting the image group compressed by the means, and the page image target data amount for the nth page image is [( Total target data amount)-{total data amount when the second compression processing is performed on the (n-1) th page images}] × (nth obtained in the first compression processing. Second page Data amount) / [(data amount of the entire image group obtained in the first compression process) − {total data of the (n−1) th page images obtained in the first compression process. Second compression means for performing the second compression processing so that
An image compression apparatus comprising: The second compression means includes
When the second compression processing that makes the page image target data amount cannot be performed, the target data amount of the page image is increased by a predetermined ratio.
The image compression apparatus according to claim 1. The above page image is assigned multiple frames,
The second compression means includes
The frame image target data amount for the m-th frame image in the order of decreasing (frame data amount / frame area) after the first compression processing is [(page image target data amount) − {(( m-1) Total amount of frame image data when second compression process is performed for up to frame images}] × (data amount of m-th frame image obtained in the first compression process) ) / [(Data amount of page image obtained in the first compression processing) − {total data amount of frame images up to (m−1) th obtained in the first compression processing}. In this way, the second compression process is performed for each frame.
The image compression apparatus according to claim 1. The second compression means includes
In accordance with the fact that a frame is allocated over the spread page image, the second compression process is performed at the same compression rate for the spread page image.
The image compression apparatus according to any one of claims 1 to 3. The second compression means includes
The first frame portion allocated to the first page image in response to the frame being allocated over the spread page image composed of the first page image and the second page image in succession. And the second frame portion assigned to the second page image are regarded as separate frames and the second compression process is performed.
The image compression apparatus according to claim 3 or 4. The second compression means includes
The first frame portion allocated to the first page image in response to the frame being allocated over the spread page image composed of the first page image and the second page image in succession. The second compression processing is performed so that the compression rate of the second frame image and the compression rate of the second frame portion allocated to the second page image are the same.
The image compression apparatus according to claim 3 or 4. A first compression unit configured to convert each page image of an image group composed of a plurality of page images to a first compression rate at which each of the compressed page images has an image quality higher than a predetermined minimum image quality; The first compression processing is performed using an initial compression ratio between the second compression ratio in which the data amount of the compressed image group is equal to or less than a predetermined overall target data amount,
The second compression means performs the second compression processing in order of decreasing data amount after compression of the page images constituting the image group compressed by the first compression means, and the nth page The page image target data amount for the image is [(total target data amount) − {total data amount when the second compression processing is performed for the (n−1) th page images}] × ( The data amount of the nth page image obtained in the first compression processing) / [(data amount of the entire image group obtained in the first compression processing) − {obtained in the first compression processing. The second compression processing is performed so that the total data amount of the (n−1) th page images is obtained}
An operation control method for an image compression apparatus. A computer-readable program for controlling a computer of an image compression apparatus,
Each page image of an image group composed of a plurality of page images is divided into a first compression rate at which each page image after compression has an image quality higher than a predetermined minimum image quality, and The first compression processing is performed using an initial compression ratio between a second compression ratio at which the data amount is equal to or less than a predetermined overall target data amount,
Page image target data for the nth page image, wherein the second compression processing is performed in ascending order of the amount of data after compression of the page images constituting the image group compressed by the first compression processing. The amount is [(the total target data amount) − {total data amount when the second compression processing is performed on the (n−1) th) page images} × (in the first compression processing). Data amount of the nth page image obtained) / [(data amount of the entire image group obtained in the first compression processing) − {(n−1) obtained in the first compression processing) A program for controlling the computer of the image compression apparatus so that the second compression processing is performed so that the total data amount of the first page image}.

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