JPH05219358A - Compressed picture data extraction device - Google Patents

Abstract

PURPOSE:To extract compressed picture data of a partial picture without expanding compressed picture data of the entire picture. CONSTITUTION:Compressed picture data Dc include coded data being Huffman- coding of one DC coefficient and 63 sets of AC coefficients for each picture element block. The DC coefficient is decoded by a DC decoding circuit 224 and the AC coefficient is decoded by an AC decoding circuit 226 to identify a delimiter of the coded data. When the DC decoding circuit 224 decodes the coded data, a count-up signal CA is outputted and accumulated by a counter 210 and whether or not a picture element block during processing is a picture element block in an extracted area is discriminated by a CPU 42 based on the count CT. The decoded DC coefficient is extracted as to a head picture element block in the extracted area and the coded data are extracted as to the other picture element DC coefficient and the AC coefficient of all the picture element blocks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for extracting a part of compressed image data for commercial printing, for example, and it is desirable to extract a desired image from compressed image data of all images encoded by sequence conversion and entropy coding. The present invention relates to a device for extracting compressed image data of a partial image.

[0002]

2. Description of the Related Art Since image data for printing plate making has a huge amount of data, a huge memory capacity is required to store the image data as it is, and a large amount of time is required for data transfer. Therefore, an image data compression method is generally used in which the amount of data is reduced by encoding the image data and compressing the image data.

Techniques such as so-called vector quantization coding and orthogonal transform coding are used as a method of compressing multi-valued image data. Discrete cosine transform (hereinafter referred to as "DCT transform") and Hadamard transform are known as the orthogonal transform. At the time of compression, the transform coefficient obtained by the series transform such as DCT transform is quantized, and the transform coefficient is further encoded by entropy coding such as Huffman coding. These compression methods are capable of compressing image data at a high compression rate, but on the other hand, the image data obtained by restoring compressed image data does not completely match the image data before compression, so-called It is a lossy encoding method.

By the way, in image processing for commercial printing, 1
In some cases, it may be desired to take out only a partial image area in one image (hereinafter referred to as “partial image”) and combine it with another image. As a method for extracting the compressed image data of partial images from the compressed image data of all images, Japanese Patent Laid-Open No. 62-18
There is a method described in Japanese Patent No. 8467. This method
The target is run-length compressed image data,
The run lengths of the compressed image data are integrated to detect the position of the run length data in all the images, and only the run length data at the position of the partial image to be extracted is extracted. In the run-length compressed compressed image data, since the run length represents the number of pixels, it is possible to extract only the compressed image data of the desired partial image by the method described above.

[0005]

On the other hand, in the case of entropy-coded compressed image data, it is difficult to obtain the image position corresponding to the compressed image data (variable length encoded data) without decompressing the compressed image data. Is. For this reason, conventionally, in order to extract the compressed image data of a desired partial image from the compressed image data, after decompressing the compressed image data of all the images, the image data of the partial images is extracted, and the extracted image data is again extracted. The compressed image data of the partial image is created by compressing. However, this method has a problem that it takes a considerable time to decompress the compressed image data of all images.

The present invention has been made to solve the above-mentioned problems in the prior art, and its object is to extract the compressed image data of the partial image without decompressing the compressed image data of the entire image. ..

[0007]

In order to solve the above-mentioned problems, an apparatus according to the invention described in claim 1 serially converts image data for each pixel block in an entire image along a scanning line in a predetermined direction. A device for extracting partially compressed image data corresponding to a partial image from the entire compressed image data created by entropy-encoding the transform coefficient, and (a) display means for displaying the entire image And (b) a region designating unit that designates a region of the partial image in the whole image displayed on the display unit,
(C) extraction area specifying means for specifying an extraction area including the specified partial image and composed of a plurality of pixel blocks; and (d) sequentially decoding the entropy coded data of the entire compressed image data, Entropy decoding means for accumulating the number of decoded data and detecting a boundary between pixel blocks in the whole compressed image data based on the number of decoded data; and (e) the pixel by the entropy decoding means. A pixel block counter that accumulates the number of pixel blocks in the entire compressed image data according to the detection of a boundary between blocks, and (f) a pixel included in the extraction region based on the count number of the pixel block counter. Extraction means for extracting the compressed image data corresponding to the block as the partial compressed image data. Further, in the compressed image data extraction device according to a second aspect of the present invention, the entire compressed image data includes entropy coded data obtained by entropy coding the DC coefficient and the AC coefficient of the discrete cosine transform, and the extracting means has a predetermined direction. Entropy coded data corresponding to the head pixel block located at the head of the extraction area when the entire image is viewed along the scanning line is detected based on the count value of the pixel block counter, and the head pixel block is D
A first means for extracting the entropy-decoded data substantially representing the C coefficient as the partially compressed image data is included.

Further, in the compressed image data extraction device according to the third aspect, the entropy-coded data of the DC coefficient in the entire compressed image data is the difference in DC coefficient between the pixel blocks adjacent to each other along the scanning line in the predetermined direction. Including entropy-encoded data obtained by entropy-encoding
Means obtains the value of the DC coefficient in each pixel block by accumulating the difference of the DC coefficient subjected to entropy decoding along the scanning line, and obtains the value of the DC coefficient in each pixel block by the accumulation. The second means for extracting the value of the DC coefficient as the partially compressed image data is included.

[0009]

The decoded data obtained by the entropy decoding means decoding the entropy coded data corresponds to the transform coefficient obtained by series-converting the image data. 1
The number of transform coefficients for one pixel block is a fixed number determined by the method of sequence conversion. Therefore, the entropy decoding unit detects the boundary between pixel blocks in the overall compressed image data by accumulating the number of transform coefficients (decoded data). The pixel block counter accumulates the number of pixel blocks according to the detection of the boundaries of the pixel blocks by the entropy decoding means.
Since the pixel blocks forming the extraction area are specified by the extraction area specifying means, the extraction means can determine whether or not each pixel block is included in the extraction area based on the count number of the pixel block counter. The compressed image data corresponding to the pixel block included in the extraction area can be extracted as the partial compressed image data.

According to a second aspect, when the whole compressed image data is created, the image data is converted by the discrete cosine transform, and the DC coefficient (DC component) and the AC coefficient (AC component) obtained by this conversion are entropy coded. Has been done. If the DC coefficient is entropy coded according to a method such as predictive coding, the image of the extraction area may not be reproduced only by the entropy coded data of the DC coefficient of the extraction area. Therefore, as described in claim 2,
The first means sets D for the first pixel block of the extraction area.
If the entropy-decoded data that substantially represents the C coefficient is extracted as the partially compressed image data, even if the DC coefficient is entropy coded by using a method such as predictive coding, the image of the extraction region is extracted by the partially compressed image data. Can be restored.

Here, "entropy-decoded data substantially representing the value of the DC coefficient" means data for which the value of the DC coefficient of the first pixel block can be obtained, and the DC coefficient of the DC coefficient can be obtained by performing some calculation. It also contains the data for which the value is required. For example, the DC coefficient value itself of the first pixel block may be used, or the difference value of the DC coefficient and the DC coefficient value of the immediately preceding pixel block may be used.

In the third aspect, the entire compressed image data is generated by entropy coding the difference of the DC coefficient. In this case, the second means can obtain the value of the DC coefficient in each pixel block by accumulating the difference between the DC coefficients that have been entropy-decoded along the scanning line. Is DC
The coefficient is extracted as partially compressed image data. As described above, since the DC coefficient of the head pixel block is extracted as the partially compressed image data, the image of the extraction area can be restored only by the partially compressed image data.

[0013]

EXAMPLES A. Overall Configuration of Apparatus FIG. 1 is a block diagram showing an image processing system as an embodiment of the present invention. This image processing system includes an image input device 30 and an image data compression device 40. The image input device 30 is, for example, a reading scanner that reads image data of a document.

The image data compression device 40 includes a CPU 42.
And a bus line 44. The bus line 44 includes a memory 46, a compression processing unit 48, and a decompression processing unit 50.
And the frame memory 52 are connected. A D / A converter 54 and a CRT 56 are sequentially connected to the frame memory 52. The bus line 44 further includes an interface 58 connected to the image input device 30 and a communication interface 60 for communicating with other external devices.
A magneto-optical disk 62 and a magnetic disk 64 for storing a large amount of image data, a keyboard 66,
The mouse 68 is connected.

B. Outline of Image Data Compressing Method and Structure of Compressed Image Data Before explaining the extracting method of the compressed image data, the outline of the image data compressing method and the structure of the compressed image data, which are prerequisites thereof, will be described. In this embodiment, image data is compressed according to the international standard method of color still image encoding (hereinafter referred to as "JPEG method"). Regarding this international standard, refer to "International Standard for Color Still Image Coding (JPE
G) (Part 1) ", Takao Omachi et al., The Institute of Image Electronics Engineers of Japan, 1991, Volume 20, No. 1, pp. 50-58.
Page.

FIG. 2 is a block diagram showing the structure of the encoding unit included in the compression processing unit 48. The coding unit has a DCT transform unit 72, a quantization unit 74, and a Huffman coding unit 76. The Huffman coding unit 76 also includes a DC coefficient coding unit 78, an AC coefficient coding unit 80, and a compressed data editing unit 82. DC
In the T conversion unit 72, the original image data Do read by the image input device 30 is two-dimensionally DCT converted. At this time, the entire image region is divided into pixel blocks of 8 × 8 pixels, and DCT conversion is performed for each pixel block. In the case of a color image, each color plate (for example, each color plate of yellow, magenta, cyan, and black) is converted.
In FIG. 3A, the entire image IP has M × N pixel blocks P.
FIG. 3 is a conceptual diagram showing a state of being divided into B, and FIG. 3B shows one pixel block PB in an enlarged manner.

8 × 8 (=) pixels in one pixel block PB
64 pieces of image data are converted into 8 × 8 conversion coefficients by DCT conversion. FIG. 4 is an explanatory diagram showing the transform coefficient F (p, q) obtained by the DCT transform. 8x
Of the eight conversion coefficients F (p, q), F (0,0) is a direct current component (hereinafter referred to as “DC coefficient”), and F (0,0)
Other than 0) are AC components (hereinafter referred to as “AC coefficients”).

The quantizing unit 74 has 64 transform coefficients F.
Linearly quantize (p, q). FIG. 5 is an explanatory diagram showing an example of a quantization table used for quantization. Each transform coefficient F (p, q) is assigned to each position (p, p,
Linear quantization is performed according to the following equation with the quantization width Ss (step size) shown in q). f (p, q) = round [F (p, q) / Ss (p, q)] (1) Here, f (p, q) is a quantized conversion coefficient, and the operator “round” "Indicates an operation for converting to the nearest integer.

The quantized transform coefficient f (p, q) is coded by the Huffman coding unit 76 and output as compressed image data Dc. In the JPEG method, the DC coefficient and the AC coefficient are encoded separately. FIG. 6 is a block diagram showing the function of the DC coefficient coding unit 78. FIG. 7 is an explanatory diagram showing the contents of data processing in the DC coefficient coding unit 78. Block delay unit 102 and adder 1
04 is the difference between the DC coefficient Fd of each pixel block and the DC coefficient Fd of the immediately preceding pixel block (hereinafter referred to as “DC difference”).
ΔFd is calculated. This is shown in Figures 7 (a) and (b).

The grouping processing unit 106 obtains the group number SSSS and the additional bit data Ad corresponding to the DC difference ΔFd according to the grouping table shown in FIG. 8 (see FIG. 7 (f)). In FIG. 7, the additional bit data Ad is shown in binary. Group number SS
As shown in FIG. 8, SS is a number determined corresponding to the range of the DC difference ΔFd, and the additional bit data Ad
Is the DC difference specified by the same group number SSSS.
It is data indicating the smallest value in the range of Fd.

The group number SSSS is further Huffman-encoded by the one-dimensional Huffman encoder 108 to generate a group number code Hd (see FIG. 7 (d)).
FIG. 9 is an explanatory diagram showing an example of the Huffman code table 110 used by the one-dimensional Huffman coding unit 108. The Huffman code table 110 of FIG.
It is a table showing the relationship between the group number SSSS of (c) and code data Hd. The code data (codeword) obtained by the Huffman coding has a variable length as can be seen from FIG.

The code data Hd and the additional bit data Ad thus created are the DC coefficient coded data CFd (see FIG. 7).
(See (g)) to the compressed data editing unit 82 (FIG. 2). As described above, the DC coefficient is converted into the code data CFd obtained by Huffman coding the DC coefficient difference ΔFd between the adjacent pixel blocks. Since the DC coefficient coded data CFd is coded based on the DC difference ΔFd, the DC coefficient coded data CF of the partial image in the image IP
Decoding d yields the DC difference. Normally, the value of the DC coefficient cannot be directly obtained from the DC difference of each pixel block. However, in the pixel block at the head of each scanning line, the DC difference ΔFd is equal to the DC coefficient Fd, and thus the value of the DC coefficient Fd can be directly obtained by decoding.

FIG. 10 is a block diagram showing the function of the AC coefficient coding unit 80. The AC coefficient Fa is first rearranged in one dimension by the zigzag scanning unit 112. Figure 1
FIG. 1 is an explanatory diagram showing a route of zigzag scanning. Further, FIG. 12A shows an example of DCT coefficients arranged in 8 rows and 8 columns, and FIG. 12B shows AC coefficients rearranged by a zigzag scan.

The determination unit 114 is arranged in the one-dimensional rearranged A
It is determined whether or not the value of the C coefficient Fa is 0. If the AC coefficient Fa is 0, the run length counter 116 converts consecutive AC coefficients of 0 into a run length count NNNN. If the AC coefficient Fa is not 0, the grouping unit 118
Thus, the group number SSSS and the additional bit data Aa are generated in the same manner as the DC coefficient. In FIG. 12 (c),
8 shows a state in which eight non-zero AC coefficients are converted into group numbers.

The run length count NNNN and the group number SSSS are Huffman-encoded by the two-dimensional Huffman encoder 120 to obtain code data Ha (FIG. 12).
(D)) is generated. FIG. 13 shows a Huffman code table 1 used by the two-dimensional Huffman coding unit 120.
It is explanatory drawing which shows an example of 22. The Huffman code table 122 is a table showing the relationship between the data arranged as shown in FIG. 12C and the code data Ha.

The code data Ha and the additional bit data Aa thus created are given to the compressed data editing unit 82 (FIG. 2) as AC coefficient coded data CFa. The compressed data editing unit 82 edits the DC coefficient coded data CFd and the AC coefficient coded data CFa to create the compressed image data Dc of the image IP.

FIG. 14 is an explanatory diagram showing the structure of the encoded data included in the compressed image data Dc. 14
As shown in, the compressed image data has the following features. (1) DC coefficient coded data CF for each pixel block
d and the AC coefficient coded data CFa are collectively stored. (2) No data for identifying the DC coefficient coded data CFd and the AC coefficient coded data CFa is inserted between them, and the coded data CFd and CFa are continuous. (3) No data for identifying the boundary of the pixel block is inserted between the group of encoded data corresponding to each pixel block. (4) Since the variable length coding is performed, the data length of the coded data of each pixel block is different.

When the image data includes a plurality of color components (for example, four YMCK components), there are two methods for arranging the color components in the compressed image data: non-interleave and interleave. In non-interleaving, coded data is arranged for one color component as shown in FIG. 14, and then coded data for the next color component is continued. On the other hand, in interleaving, after arranging the encoded data of each component of YMCK for each pixel block,
Continue with the encoded data for the next pixel block. In this embodiment, a case will be described in which compressed image data generated according to non-interleave is extracted.

C. Configuration and Operation of Decompression Processing Unit FIG. 15 is a block diagram showing the internal configuration of the decompression processing unit 50 for extracting compressed image data and other circuit elements related to the extraction of compressed image data. Expansion processing unit 50
Is a decoding circuit 202, a first buffer 204, an integrating circuit 206, a counter 210, and a second buffer 21.
2, an IDCT conversion circuit 214, and a memory 216. The IDCT conversion circuit 214 is a circuit that performs inverse DCT conversion when decompressing the compressed image data, and is not used during the extraction process of the compressed image data. The input interface 41 and the output interface 43 of the CPU 42, which are omitted in FIG. 1, are also illustrated.
The decoding circuit 202 includes a separation circuit 222 and a DC decoding circuit 2
24 and an AC decoding circuit 226.

The display means in the present invention is the CRT 5
6 (FIG. 1), and the area designating means is realized by a keyboard 66 and a mouse 68. Further, the extraction area specifying means is realized by the processing contents executed by the CPU 42 by the program stored in the ROM 46a. The entropy decoding means is realized by the decoding circuit 202. The pixel block counter is realized by the counter 210, and the extraction means is realized by the processing contents executed by the CPU 42 by the program stored in the ROM 46a.

FIG. 16 is a flowchart showing the procedure of the extraction process of compressed image data. FIG. 17 is an explanatory diagram showing the entire area of the image IP and the partial image PIP that is the target of the extraction processing. In FIG. 17, (x, y) are pixel coordinates, and (m, n) are pixel block coordinates. Here, y and n are coordinate axes in the main scanning direction, and x and m are coordinate axes in the sub scanning direction. FIG. 18 is an explanatory diagram showing the configuration of the compressed image data EDc created by the extraction process.

First, in step S1 of FIG. 16, a reduced image of an image to be processed is displayed on the CRT 56. The reduced image data representing the reduced image is prepared in advance by thinning out the original image data and stored in the magnetic disk 64. In step S2, the operator uses the keyboard 66 or the mouse 68 to instruct to perform the extraction processing of the compressed image data.

In step S3, the CPU 42 resets the counter 210 via the output interface 43 in accordance with the instruction in step S2. The counter 210 is a circuit for counting the number of pixel blocks, as described later. In step S3, the header of the compressed image data Dc stored on the magnetic disk 64 is read by the CPU 42 via the input interface 41, and the memory 216 is read.
The content is stored in the header area of (corresponding to the header of FIG. 18).

FIG. 19 is an explanatory diagram showing the contents of the header of the compressed image data. In the header, the size of the entire image IP (in number of pixels), the number of color components (4 in the case of YMCK), the compression flag indicating the compression method, the number of pixel blocks in the main scanning direction and the sub scanning direction of the extraction area EA. , Extraction area E
Offset address of A (pixel number unit), compression rank (indicating compression level), quantization table (FIG. 5),
And a Huffman code table (FIGS. 9 and 13).

The quantization table and the Huffman code table are transferred from the CPU 42 via the output interface 43 to the DC decoding circuit 224 and the AC decoding circuit 226 in the decoding circuit 202 and stored therein.

In step S4, the area of the partial image to be extracted in the reduced image displayed on the CRT 56 is designated by using the mouse 68. In FIG. 17, when the operator specifies the positions of the two points P1 and P2 with the mouse 68, the coordinates (x1, y1), (x2, y2) of these points are set.
Are provided to the CPU 42, respectively. The CPU 42 calculates the coordinates (m1, n1), (m2, n2) of the pixel blocks PB1, PB2 including the points P1, P2 based on these coordinates (x1, y1), (x2, y2) using the following formula. Calculate according to. m1 = INT (x1 / Px) +1 (2) n1 = INT (y1 / Py) +1 (3) m2 = INT (x2 / Px) +1 (4) n2 = INT (y2 / Py) +1 ((4)) 5) Here, the function “INT” indicates an operation of truncating the value in parentheses after the decimal point. Further, Px and Py indicate the numbers of pixels in the x direction and the y direction of the pixel block, respectively.

The partial image PIP designated by the operator is
As shown in FIG. 17, it is a rectangular region having two points P1 and P2 as diagonal vertices. On the other hand, the area from which the compressed image data is extracted (hereinafter referred to as “extracted area”) is composed of all pixel blocks including at least a part of this partial image PIP. In FIG. 17, the extraction area EA
Is surrounded by a thick solid line.

In step S5, one pixel block worth of D is extracted from the compressed image data Dc by the decoding circuit 202.
The C encoded data is decoded. FIG. 20 shows step S5.
3 is a flowchart showing the details of the above. In step S21, only 1 bit of the encoded data included in the compressed image data Dc is separated by the separation circuit 2 of the decoding circuit 202.
22 read. The separation circuit 222 is a circuit that separates the DC coefficient coded data CFd and the AC coefficient coded data CFa, and is initialized so that the encoded data is given to the DC decoding circuit 224 at the initial stage of the extraction process of the compressed image data. Has been done.

In step S22, the DC decoding circuit 224
Refers to the DC coefficient Huffman code table 110 (FIG. 9) and compares the coded data read in step S21 with the code word of the Huffman code table 110. If the encoded data read in step S21 does not match one of the code words in the Huffman code table 110, the process returns from step S23 to S21, and another encoded data is added.
Read by adding a bit. When the coded data matches any code word in the Huffman code table 110 in step S22 (that is, when the coded data is decoded), the process passes through step S23 to step S23.
24 is executed.

In step S24, the calculation of the DC coefficient and the switching of the separation circuit 222 are performed as follows.
First, when the DC decoding circuit 224 decodes the encoded data, the DC decoding circuit 224 gives the count-up signal CA to the integrating circuit 206, the register 208, and the counter 210.

The integrating circuit 206 and the register 208 are DC
It has a function of obtaining the DC coefficient of each pixel block based on the decoded data (DC difference data ΔS) output from the decoding circuit 224. The integrating circuit 206 stores the DC difference data ΔS in the register 20 according to the count-up signal CA.
8 is added to the data in 8 and the data in the register 208 is updated by the data SU obtained by the integrating circuit 206.
The data SU output from the integrating circuit 206 is the DC coefficient of each pixel block. However, in order to match the output from the integrating circuit 206 with the DC coefficient, before processing the encoded data of the pixel block at the beginning of each scanning line (pixel block shown by hatching in FIG. 3A), the register 208
The data inside is initialized to 0 by the CPU 42. It should be noted that the compressed image data Dc includes a marker that indicates the beginning of the scanning line before the encoded data of each scanning line starts, and the contents of the register 208 are initialized according to the detection of the marker. To be done.

The counter 210 has a count-up signal C.
By counting the number of A pulses, the number of pixel blocks in the compressed image data is substantially counted along each scanning line, and the count value CT is given to the CPU 42. The counter 210 is initialized to 0 by the CPU 42 at the beginning of the process of extracting the compressed image data.

In step S24, a switching signal is further given from the DC decoding circuit 224 to the separation circuit 222.
When the separation circuit 222 is switched, the magnetic disk 64
The encoded data read from the separation circuit 222 is A
It is supplied to the C decoding circuit 226.

Thus, step S5 (S21 to S24)
16 is executed, the CPU 4 determines whether the pixel block corresponding to the coded data being processed is the leading pixel block of the extraction area EA.
Judged by 2. Here, the leading pixel block of the extraction area EA is a pixel block in the main scanning direction coordinate n having the minimum value n1 among the pixel blocks in the extraction area EA. In FIG. 17, the leading pixel block at the top of the extraction area EA is shaded in only one direction.

In step S6, it is determined whether or not the pixel block being processed is the leading pixel block of the extraction area EA. When the following expressions (5) and (6) are satisfied, the pixel block is the head pixel block. MOD (CT, N) = n1 (6) m1 ≦ INT [(CT-1) / N] ≦ m2 (7) Here, the function “MOD” has the first value in parentheses as the second value. The calculation shows the remainder when the value is divided. CT is the count value of the counter 210, N is the number of pixel blocks in the main scanning direction of the entire image IP (FIG. 3), n1 is the minimum pixel block coordinate in the main scanning direction of the extraction area EA, and m1 and m2 are the extraction area EA. 2 is the minimum value and the maximum value of the pixel block coordinates in the sub-scanning direction.

If the pixel block being processed is the head pixel block, a marker indicating that it is the data of the head pixel block is written in the memory 216 by the CPU 42 and then output from the integrating circuit 206 in step S7. The DC coefficient SU is written in the memory 216 via the buffer 212. As shown in FIG. 18, the first
The marker of the th first pixel block is written at the address immediately after the header, and the DC coefficient SU is written after that. The header, marker, and DC coefficient SU are fixed-length data. The case where the pixel block being processed is not the first pixel block will be described later.

When the DC coefficient SU of the head pixel block is written in the memory 216, the AC coefficient of the head pixel block is decoded in step S11. Figure 21
3 is a flowchart showing a detailed procedure of step S11. In step S31, the encoded data included in the compressed image data Dc is read by the separation circuit 222 of the decoding circuit 202 by 1 bit. Separation circuit 222
Is the AC decoding circuit 2 in step S24 (FIG. 19).
26 has been switched to provide encoded data.

At step S32, the AC decoding circuit 226.
Is the Huffman code table 122 for AC coefficients (FIG. 13)
With reference to, the coded data read in step S31 and the code word of the Huffman code table 122 are compared. The procedure of steps S31 to S33 is D shown in FIG.
This is the same as the procedure S21 to S23 for decoding the C coefficient.

In step S34, it is determined whether or not the pixel block being processed is a pixel block in the extraction area EA. When the following expressions (8) and (9) are satisfied, the pixel block is in the extraction area EA. n1 ≦ MOD (CT, N) ≦ n2 (8) m1 ≦ INT [(CT-1) / N)] + 1 ≦ m2 (9)

When the pixel block being processed is a pixel block in the extraction area EA, A is determined in step S35.
The C coefficient coded data CFa is written in the memory 216 as it is. As shown in FIG. 18, the AC coefficient coded data CFa of the first pixel block PB (m1, n1)
Is written immediately after the decoded DC coefficient SU. On the other hand, when the pixel block being processed is not the pixel block in the extraction area EA, the AC coefficient coded data CFa is not written in the memory 216 as shown in step S37, and the process proceeds to the next step S37.

In step S37, it is judged whether or not the decoding of the AC coefficients for one pixel block (63 pieces) is completed. If not completed, the process returns to step S31 and the above-mentioned processing is repeated.

When the AC coefficient for one pixel block is decoded, the switching signal is changed to the AC decoding circuit 2 in step S38.
26 to the separation circuit 222, and the separation circuit 222 is switched to the DC decoding circuit 224 side. Thus, FIG.
6 step S11 (steps S31 to S3 in FIG. 21)
When step 8) ends, the process moves to step S12.

In step S12, it is determined whether the pixel block being processed is the final block in the extraction area EA. The final block is a pixel block PB2 whose coordinate value (m, n) is equal to the maximum value (m2, n2) of the extraction area EA (see FIG. 17). When the following expressions (10) and (11) are satisfied, it is the final block in the extraction area EA. MOD (CT, N) = n2 (10) INT [(CT-1) / N)] + 1 = m2 (11) If it is not the final block, the process returns to step S5, and steps S5 to S12 are repeated.

By the way, if it is determined in step S6 that the pixel block being processed is not the head pixel block, the following process is executed. First, in step S8, the pixel block being processed is the extraction area EA.
It is determined whether or not the pixel block is a pixel block in. When the following equations (8) and (9) are satisfied, the pixel block is in the extraction area EA.

If it is a pixel block in the extraction area EA, in step S9 the DC coefficient coded data CFd
Is written in the memory 216 as it is. As shown in FIG. 18, the encoded data of the pixel blocks other than the first pixel block on each scanning line is DC coefficient encoded data CFd,
The AC coefficient coded data CFa is continuously written in each pixel block. On the other hand, when the pixel block being processed is not the pixel block in the extraction area EA, as shown in step S10, the DC coefficient coded data CFd is not written in the memory 216 and the process proceeds to step S11.
The above-described AC coefficient decoding process is executed.

As described above, when the coded data of the first pixel block of the extraction area EA is extracted, the marker is written in the memory 216, the decoded DC coefficient SU is written, and the AC coefficient coded data CFa is written. Write. Further, in the other pixel blocks in the extraction area EA, the DC coefficient coded data CFd and the AC coefficient coded data CFa are continuously written as they are. As a result, the compressed image data EDc shown in FIG. 18 is created.

The coded data is extracted as it is from the pixel blocks other than the first pixel block, but as described above, the Huffman-coded coded data is also decoded at that time. This is because, as shown in FIG. 14, the encoded data included in the compressed image data of the entire image IP is variable-length data, so the encoded data must be collated with the Huffman code table. This is because the boundary between the pixel blocks in the encoded data cannot be identified.

In the pixel blocks other than the first pixel block, it is sufficient that the boundaries between the pixel blocks in the encoded data can be discriminated, so that the decoded data is not obtained,
It may be possible to determine only whether the encoded data matches one of the Huffman codewords.

As shown in FIG. 18, in the extracted compressed image data EDc, the header, the marker, and the DC coefficient SU of the first pixel block are fixed length data, and the coded data that follows is a variable length data. is there. Note that, in FIG. 18, for convenience of illustration, the compressed image data on one scanning line is collectively shown in one line. At the end of the variable length encoded data of each scanning line, data for byte alignment (indicated by diagonal lines in FIG. 18) is added so that the data length of the variable length encoded data becomes an integral multiple of 8 bits. Has been done.

As described above, in this embodiment, when the compressed image data is extracted, it is detected that the encoded data in the compressed image data matches one of the code words in the Huffman code table, and each code is detected. After identifying the delimiter between the encoded data, the encoded data is used as it is for the extracted compressed image data. In the compressed image data after extraction, the extraction area E
As the DC coefficient data of the head pixel block of A, the DC coefficient obtained by decoding the encoded data is used, and a marker indicating the head pixel block is written before the decoded DC coefficient. ing. That is, this embodiment has an advantage that it is not necessary to decompress the compressed image data of all the images, and the compressed image data of the desired extraction area EA can be extracted only by decoding the Huffman-encoded encoded data. is there.

The present invention is not limited to the above embodiments, but can be carried out in various modes without departing from the scope of the invention, and the following modifications can be made.

(1) The present invention is applicable not only to image data composed of YMCK image components but also to extraction of compressed image data composed of BGR components and CIE color system components. It is also applicable to image data containing only one color image component. In general, the present invention can be applied to the extraction of multivalued compressed image data.

(2) In the above embodiment, the image data is compressed by encoding the image data by the DCT transform and the Huffman encoding, but the present invention is generally a compressed image compressed by the sequence conversion and the entropy encoding. Applicable when extracting data. As the sequence transformation, for example, orthogonal transformation such as Fourier transformation or Hadamard transformation, vector quantization coding, or the like can be used. Further, arithmetic coding or the like can be used as the entropy coding.

(3) In the compressed image data after extraction,
Data S decoded as the DC coefficient of the first pixel block
Although U is used, the DC coefficient SU once decoded may be compressed by predictive coding or Huffman coding, and the coded data may be recorded next to the marker. In the above embodiment, the decoded DC coefficient SU is used in J
This is because the DC coefficient difference ΔFd is Huffman-encoded in the PEG method, and therefore the DC coefficient SU of the first pixel cannot be directly calculated from the encoded data.

When extracting a part of the compressed image data created by encoding the DC coefficient Fd itself instead of the DC coefficient difference ΔFd, the encoded data is used as it is for the first pixel block as well. It is possible to create compressed image data of.

As another configuration of the compressed image data after extraction, the encoded data may be used as it is for the head pixel block, and the value of the DC coefficient of the pixel block before the head pixel block may be stored. .. At this time, the DC coefficient of the pixel block before the first pixel block may be losslessly encoded and stored. That is, generally, it is sufficient that the data substantially representing the DC coefficient is extracted for the first pixel block.

(4) In the above embodiment, the calculation for obtaining the difference ΔFd of the DC coefficient is a kind of predictive coding. Huffman coding is a kind of entropy coding. That is, in the compression method of the above embodiment, the entropy coding (Huffman coding) is performed after the predictive coding (calculation of the difference) is performed on the DC coefficient. The present invention can also be applied to extraction of compressed image data using predictive coding other than the difference. When the predictive coding according to the prediction formula other than the difference is used, the DC coefficient of the head pixel block is calculated according to the prediction formula so that the DC coefficient of the head pixel block can be calculated only by the extracted compressed image data. It suffices to extract the data that substantially represents.

(5) The range of the extraction area EA is CRT56.
Although the operator designated it using the mouse 68 on the reduced image displayed on the screen, instead of this, the operator inputs the width dimension (pixel number) of the extraction area EA using the keyboard 66. Good.

(6) As an image display device, a CRT 56
Other image output devices such as a color printer may be used instead of the above.

(7) In the above embodiment, a part of the compressed image data is extracted from the non-interleaved compressed image data, but the present invention can be applied to the extraction of the compressed image data generated according to the interleave. In this case, the number of pieces of decoded data serving as a reference when the AC decoding circuit 226 switches the separation circuit 222 may be changed according to the interleaving method.

[0071]

As described above, according to the first aspect of the present invention.
According to the invention described in (1), the entropy decoding unit detects the boundary between pixel blocks in the entire compressed image data by accumulating the number of decoded data (transform coefficients) obtained by decoding the entropy coded data. Then
The pixel block counter accumulates the number of pixel blocks according to the detection of the boundaries of the pixel blocks by the entropy decoding means. Since the pixel blocks forming the extraction area are specified by the extraction area specifying means, the extraction means can determine whether or not each pixel block is included in the extraction area based on the count number of the pixel block counter. The compressed image data corresponding to the pixel block included in the extraction area can be extracted as the partial compressed image data. That is, according to the invention described in claim 1, there is an effect that the compressed image data of the extraction region including the partial image can be extracted without expanding the compressed image data to the image data.

According to the invention described in claim 2,
Since the entropy-decoded data that substantially represents the DC coefficient is extracted as the partial compressed image data for the first pixel block of the extraction area, even when the DC coefficient is entropy-coded using a method such as predictive coding, ,
There is an effect that the image of the extraction area can be restored by the partially compressed image data.

Further, according to the invention described in claim 3, since the DC coefficient is extracted as the partial compressed image data for the head pixel block, when the DC coefficient is entropy coded based on the difference of the DC coefficient. Also,
There is an effect that the image of the extraction area can be restored by the partially compressed image data.

[Brief description of drawings]

FIG. 1 is a block diagram showing an image processing system for compressing image data by applying an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an encoding unit provided in a compression processing unit 48.

FIG. 3 is an explanatory diagram showing pixel blocks in an image.

FIG. 4 is a diagram showing transform coefficients F (p, p,
Explanatory drawing which shows q).

FIG. 5 is an explanatory diagram showing an example of a quantization table used for quantization.

FIG. 6 is a block diagram showing the function of a DC coefficient encoding unit 78.

FIG. 7 is an explanatory diagram showing the content of data processing in a DC coefficient encoding unit 78.

FIG. 8 is an explanatory diagram showing a grouping table.

FIG. 9 is an explanatory diagram showing a one-dimensional Huffman code table for DC coefficients.

FIG. 10 is a block diagram showing functions of an AC coefficient coding unit 80.

FIG. 11 is an explanatory diagram showing a route of zigzag scanning.

FIG. 12 is an explanatory diagram showing DCT coefficients arranged in 8 rows and 8 columns and AC coefficients rearranged by a zigzag scan.

FIG. 13 is an explanatory diagram showing a two-dimensional Huffman code table for AC coefficients.

FIG. 14 is an explanatory diagram showing a configuration of a portion of encoded data included in compressed image data Dc.

FIG. 15 is a block diagram showing circuit elements related to extraction of compressed image data.

FIG. 16 is a flowchart showing a procedure of compressed image data extraction processing.

FIG. 17 is an explanatory diagram showing the entire area of the image IP and a partial image PIP that is the target of extraction processing.

FIG. 18 is an explanatory diagram showing a configuration of compressed image data EDc created by extraction processing.

FIG. 19 is an explanatory diagram showing the content of the header of the extracted compressed data.

FIG. 20 is a flowchart showing the details of the decoding process of the DC encoded data in step S5.

FIG. 21 is a flowchart showing a detailed procedure of decoding processing of AC encoded data in step S11.

[Explanation of symbols]

 30 image input device 40 image data compression device 41 input interface 42 CPU 43 output interface 44 bus line 46 memory 48 compression processing unit 50 decompression processing unit 52 frame memory 54 D / A converter 56 CRT 58 interface 60 communication interface 62 magneto-optical disk 64 magnetic disk 66 keyboard 68 mouse 72 DCT conversion unit 74 quantization unit 76 Huffman coding unit 78 DC coefficient coding unit 80 AC coefficient coding unit 82 compressed data editing unit 102 block delay unit 104 adder 106 group Conversion processing unit 108 1-dimensional Huffman coding unit 110 1-dimensional Huffman coding table 112 Zigzag scanning unit 114 Judgment unit 116 Run length counter 118 Grouping unit 120 Two-dimensional Huffman coding unit 12 Two-dimensional Huffman code table 202 Decoding circuit 206 Accumulation circuit 208 Register 210 Counter 212 Buffer 214 IDCT conversion circuit 216 Memory 222 Separation circuit 224 DC decoding circuit 226 AC decoding circuit Aa Additional bit data Ad Additional bit data CA Count up signal CFa AC coefficient code CFd DC coefficient coded data Dc Compressed image data Do Original image data EA Extraction area EDc Compressed image data after extraction F DCT conversion coefficient Ha Huffman code data Hd Huffman code data IP whole image PB pixel block PIP partial image NNNN run length Count SSSS Group number SU Decoded DC coefficient data m Sub scanning direction pixel block coordinates n Main scanning direction pixel block coordinates x Sub scanning direction pixel coordinates y Scanning direction pixel coordinates

Claims (3)

[Claims] 1. A part of the whole compressed image data created by performing a series conversion of the image data for each pixel block in the whole image along a scanning line in a predetermined direction and entropy coding the conversion coefficient. An apparatus for extracting partially compressed image data corresponding to an image, comprising: (a) display means for displaying the whole image; and (b) designation of a partial image area within the whole image displayed on the display means. (C) extraction area specifying means for specifying an extraction area including the specified partial image and composed of a plurality of pixel blocks; and (d) entropy-encoded data of the entire compressed image data. Are sequentially decoded, the number of decoded data is accumulated, and the boundary between pixel blocks in the overall compressed image data is detected based on the number of decoded data. And (e) a pixel block counter that accumulates the number of pixel blocks in the overall compressed image data in response to detection of boundaries between the pixel blocks by the entropy decoding unit. A compressed image data extraction device, comprising: an extraction unit that extracts, as partial compressed image data, compressed image data corresponding to a pixel block included in the extraction area based on the count number of the pixel block counter. 2. The compressed image data extraction device according to claim 1, wherein the entire compressed image data includes entropy coded data obtained by entropy coding the DC coefficient and the AC coefficient of the discrete cosine transform, and the extraction means , Entropy coded data corresponding to the head pixel block located at the head of the extraction area when the entire image is viewed along the scanning line in the predetermined direction is detected based on the count value of the pixel block counter, and the head pixel is detected. A compressed image data extraction device including first means for extracting entropy-decoded data substantially representing the DC coefficient as a block as partial compressed image data. 3. The compressed image data extraction device according to claim 2, wherein the entropy-encoded data of the DC coefficient in the entire compressed image data is a DC coefficient between adjacent pixel blocks along a scanning line in a predetermined direction. The first means includes entropy coded data that is entropy coded and the first means is DC in each pixel block by accumulating the differences of the entropy decoded DC coefficients along the scan line.
A compressed image data extraction device including second means for obtaining the coefficient value and extracting the DC coefficient value obtained by the accumulation as partial compressed image data for the first pixel block.