JPH05199416A - Method and device for picture processing - Google Patents

Abstract

PURPOSE:To efficiently compress and store picture data by encoding input data by stages corresponding to frequencies and storing the correspondence between respective stages and storage areas. CONSTITUTION:A color conversion part 1 obtains Y, U, and V of picture data of RGB, and a subsampling part 2 subsamples Y, U, and V. A DCT part 3 obtains DCT coefficients by frequency conversion. A quantizing part 4 uses a table 5 to quantize DCT coefficients, and quantized coefficients are one- dimensionally transposed from the lower frequency component to the higher frequency component. In this progressive encoding of quantized coefficients, each component is divided into four stages and is encoded to Huffman codes by encoding parts 6 to 9. Data in each stage is written in a compression memory 13. A segment in the memory 13 is selected by a selector 11, and its information is held in a table 12. Thus, encoding to Huffman codes is performed by one scan, and the scan time is shortened and the large-capacity memory is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for compressing image data.

[0002]

2. Description of the Related Art In recent years, ADCT (Adaptive Discrete Cosine Transform) has been used mainly for natural images as a compression technique for multivalued images.
A compression method is about to be proposed. This compression method is
Converting the three primary color (RGB) signals into three components of Y, U, V,
The Y signal, which is the luminance, has the same resolution as it is, and the U and V signals of the chromaticity component are sometimes sub-sampled,
It uses a procedure that reduces the resolution and compresses. In the compression step 1, DC is calculated for each 8 × 8 block for each component.
Then, it is transformed into an 8 × 8 frequency space and DCT coefficients are obtained. In step 2, two kinds of quantization tables of the luminance component (Y) and the chromaticity component (U, V) are prepared, and D
The CT coefficient is linearly quantized (divided) by an 8 × 8 quantized value obtained by multiplying each element of the 8 × 8 quantization table by a quantization factor for each component, and a quantized coefficient is obtained. In step 3, this quantized coefficient is Huffman-encoded using the Huffman encoding method which is a variable length encoding method.

There are two types of Huffman coding: sequential coding and progressive coding. Sequential coding is a method in which all 64 quantized coefficients quantized for one block are coded, and then the quantized coefficients of the next block are coded. In this method, all the color components or a part of the color components of one image are encoded by one scan, and the decoded images obtained by the procedure after this encoding are sequentially displayed from the top in the sub-scanning direction. It

Further, the progressive coding is a method in which 64 quantized coefficients quantized for one block are divided into a plurality of stages, and scanning is performed for each stage to perform coding. Therefore, if the quantized coefficient is divided into, for example, 5 stages, 5 scans are required. This decoded image is displayed in a stepwise manner so that the resolution and gradation are successively improved after a rough decoded image having low resolution and gradation is displayed from top to bottom.

[0005]

However, when compression is performed by the compression method according to the above-mentioned conventional example, the Huffman coding method is a variable length coding method, and therefore, the amount of compressed data remains until the coding is completed. There is a drawback that the target amount of compressed data cannot be controlled without knowing it.

Further, in the Huffman coding method, when the progressive coding method is used, the scanning is performed a plurality of times, so that it takes time and it is necessary to save the image data of each scan at the time of decoding. However, there is a drawback that a large capacity memory for one image is required.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object thereof is to provide an image processing apparatus and method capable of efficiently compressing and storing image data. There is a point.

[0008]

[Means for Solving the Problems]
In order to achieve the object, the image processing method according to the present invention encodes the input frequency conversion data in stages according to frequency, and independently encodes the frequency conversion data in each stage encoded in a plurality of storage areas. And storing the correspondence between each of the stages and the storage area. Further preferably, the image processing apparatus according to the present invention is a storage means having a plurality of storage areas, an encoding means for encoding the input frequency conversion data for each quantization step according to a frequency, and the quantization step. Writing means for writing the coded data obtained by the encoding means to the plurality of storage areas, wherein the writing means includes a first storage area of the first storage area of the plurality of storage areas. If the writing of the second step of the quantization step to the second storage area is completed during the writing of the first step, the free storage areas of the plurality of storage areas are further left over in the second step. It is characterized by writing the encoded data of.

[0009]

According to the above, the input frequency conversion data is encoded in stages according to the frequency, and the encoded frequency conversion data of each stage is independently stored in a plurality of storage areas. If you store the correspondence with the storage area,
Image data can be compressed and stored efficiently.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. <First Embodiment> FIG. 1 is a block diagram showing the arrangement of an image processing apparatus according to the first embodiment of the present invention. In the figure, 1 is a color conversion unit, 2 is a sampling unit, and 3 is a DCT.
(Discrete cosine transform) unit, 4 quantization unit, 5 quantization table, 6 to 9 Huffman coding unit, 10 Huffman table, 11 segment selector, 12 segment information table, 13 compression memory, 14 A CPU for controlling the entire apparatus, and 15 for operating the CPU 14 shown in FIG.
The ROM that stores data such as a program in accordance with the flow chart of the above, and 16 are RAMs used as work areas of various programs.

The operation of the above configuration will be described.

FIG. 2 is a diagram for explaining the zigzag scan of the quantized coefficient according to the first embodiment, and FIG. 3 is a diagram for explaining the progressive coding step structure and the quantized coefficient in the first embodiment. FIG. 4 is a diagram for explaining the contents of the compression memory according to the first embodiment, and FIG. 5 is a diagram for explaining the segment information table for each stage according to the first embodiment.

The color conversion unit 1 converts the RGB image data into Y, Y by 3 × 3 linear matrix conversion expressed by the following equation (1).
U and V are required. That is, the formula (1) is

[0014]

[Equation 1] Becomes

Y indicates a luminance component, and U and V indicate chromaticity components. The sub-sampling unit 2 performs sub-sampling of Y, U, and V by utilizing the fact that the sensitivity characteristics of the human eye are more sensitive to the luminance component Y than to the chromaticity components U and V. In this case, conversion and sampling are performed at a ratio of Y: U: V = 4: 1: 1 or 4: 2: 2. Next, the DCT unit 3 performs DCT for each 8 × 8 block for each of Y, U, and V, and frequency conversion is performed for each 8 × 8 block. Hereinafter, this transformed coefficient will be referred to as a DCT coefficient.

In the quantizer 4, the DCT coefficient is
Each 8 × 8 block is quantized using the quantization table 5. Hereinafter, this quantized coefficient is referred to as a quantized coefficient. The 8 × 8 two-dimensional quantized coefficients are rearranged one-dimensionally from low frequency components to high frequency components by zigzag scanning as shown in FIG. In the progressive coding, the quantized coefficients arranged in one dimension are shown in FIG.
, The low-frequency component to the high-frequency component is divided into several stages (stage (1) to stage (4)), and the stage (1) is processed by the Huffman encoder 6 in the stage (2).
Is Huffman coded by the Huffman code unit 7, stage (3) by the Huffman code unit 8 and stage (4) by the Huffman code unit 9. However, the Huffman coding units 6 to 9 all perform Huffman coding using the same Huffman table 10. Hereinafter, the data obtained by the Huffman coding will be referred to as coded data.

The compression memory 13, as shown in FIG. 4, is divided into segments (for example, 1 segment = 100k).
B) has a configuration in which S-1 to SN are separated. Further, the segment information table 12 has a structure as shown in FIG. The first to fourth rows of the segment information table 12 are respectively stages (1) to
This is information regarding (4). The first column shows the selected segment number (S-1 to SN) of the compression memory 13 to which the encoded data of each stage is written. As the process progresses from left to right, the sequence proceeds from the beginning to the end of the image. Show. Further, END indicates that the coded data in each stage is completed.

Next, the procedure for writing the encoded data in the compression memory 13 for each stage will be described.

FIG. 6 is a flow chart for explaining the compression processing according to the first embodiment.

In this embodiment, since the Huffman coding system which is a variable length coding system is used, the code amount in each stage also differs. The code amount depends on the original image data, but when a natural image is used as the original image, the power is generally concentrated on the low frequency component.
Therefore, when comparing the stages (1) to (4), the code amount output from the stage (4) is larger in the stage (1).

Based on the above, the flow chart of FIG. 6 will be described below with reference to FIG.

As shown in the second column (column N0.2) of FIG. 5, the encoded data output at each stage is segment S-1, S-2, S-3, S-4, respectively. Written in. Then, in the stage (1), since the data of the low frequency component is encoded, the segment S-1 is filled earlier than the other stages, so that the writing is started in the segment S-5. Next, in the stages (2) and (3), since writing to the segments S-2 and S-3 is satisfied, writing to the segments S-5 and S-6 is started (steps). S101).

At the next stage, since the stage (1) has finished writing to the segment S-5 before the stage (4) has finished writing to the segment S-4, there is no space. The existing segment S-8 is not assigned to the stage (4) but is assigned to the stage (1). This occurs because the code amount generated in the stage (1) is larger than that in the stage (4). Similarly, at each stage, if the segment to be written is satisfied, the vacant segment is selected and the encoded data is written there (step S102,
Step S103, Step S104).

In the present embodiment, the method of dividing the original image into several stages and encoding is used. Therefore, when the encoded data amount of each stage is smaller than the target compression (code) memory amount, the invalid stage does not appear, but when the target compression (code) memory amount is reached during encoding. , The designated stage is invalidated (stage (4) in FIG. 5), and the segments S-4, -11, S-15, ... Assigned to the stage (4) have other stages (1) to (3). ) Coded data is written. The description corresponds to the 8th to 11th columns (No. 8 to N in FIG. 5).
o. 11). On stage (2) in the 8th row,
Since the segment SN has been allocated, the compression memory 1
Since all 3 are allocated, compressed memory 13
In order to make up for the shortage of the segment (4), the stage (4) is invalidated (“0”), and the segment S-4 used in the stage (4) is replaced with the stage (1) as shown in the ninth column. And segment S-11 is used for stage (2). Since the encoding of the stage (2) is completed in the segment S-11, the END mark is added to FIG. 5 thereafter. Further, in the stage (1), the segment 15 used in the stage (4) is allocated as in the tenth column, and since the encoding is completed thereafter, the END mark is added (step S105).

On the other hand, regarding decompression of the compressed data stored in the compression memory 13, at the time of decompression, the image data is decoded using only the valid stages (1) to (3). The Huffman coding units 6 to 9 have four Huffman decoding units, the Huffman table 10 has a Huffman decoding table for decoding the tables, and the quantizing unit 4 has an inverse quantizing unit and a quantizing table 5. The inverse quantization table and the inverse DCT unit in the DCT unit 3 may be provided so as to correspond to each other.

In this case, the segment selector 11 transfers the encoded data of each stage from the compression memory 13 to the above four Huffman decoding units according to the segment information table 12. The four Huffman decoding units perform a process of decoding the encoded data of each stage using the Huffman decoding table and transferring the decoded data to the dequantization unit. In this dequantization unit, dequantization is performed for each 8 × 8 block from the decoded data of all valid stages. The inverse DCT unit performs an inverse DCT conversion on the data of the inverse quantization unit for each 8 × 8 block. When the sub-sampling ratio is 4: 1: 1, the sub-sampling unit in the case of expansion Y1, Y2, Y3,
Y4, U1, V1 ... to Y1, Y2, Y3, Y4, U1,
U1, U1, U1, V1, V1, V1, V1 ...
When 4: 2: 2, Y1, Y2, U1, V1 ...
The conversion is performed so as to be 1, Y2, U1, U1, V1, V1 ... Further, in the case of decompression, the color conversion unit performs the process of performing the inverse conversion of the equation (1).

In this way, the compressed data may be expanded.

As described above, using the compression memory 13 divided into a plurality of segments, the segment selector 11 for selecting the segment, and the segment information table 12 for storing the information, the progressive code is obtained by one scan. (Huffman coding)
It is possible to shorten the scan time by reducing the number of scans, reduce the large-capacity memory for one image, and achieve fixed-length compression. <Second Embodiment> Next, a second embodiment will be described.

FIG. 7 is a block diagram showing the structure of the image processing apparatus according to the second embodiment of the present invention. In the figure,
21 is a color conversion unit, 22 is a sampling unit, and 23 is a DCT
Section, 24 is a quantization section, 25 is a quantization table, 34 is a band Huffman coding section, 30 is a Huffman table, 31 is a segment selector, 32 is a segment information table,
33 is a compression memory, and 36 is a CP that controls the entire device.
U and 37 are ROMs storing data such as the program of FIG. 8 according to the flow chart for the CPU 36 to operate,
38 is an RA used as a work area for various programs
M is shown respectively. A circuit having the same name as in FIG. 1 has the same function as in FIG.

In FIG. 7, a plurality of Huffman coding units in FIG. 1 are realized by one band Huffman coding unit 34, and an object thereof is to simplify the circuit structure of the progressive coding in FIG. ..

Next, the procedure for writing the encoded data in the compression memory 33 for each stage will be described.

The quantized coefficients quantized by the quantizer 24 are input to the band Huffman encoder 34 in order from the low frequency component by zigzag scanning. The band Huffman coding unit 34 performs Huffman coding from low frequency components.
When the encoding of the area of the stage (1) is completed as in the first embodiment, the segment S-1 is selected by the segment selector 31. The encoded data obtained by the Huffman encoding is transferred to the selected segment S-1, and the number S-1 of the segment S-1 is written in the segment information table 22.

Next, the area of the stage (2) is coded, and the segment selector 31 selects the segment S-2.
Is selected. The obtained encoded data is the segment S-
2, and the number S-3 of the segment S-2 is written in the segment information table. Then, the region of the stage (3) is encoded, and the segment selector 31 selects the segment S-3. The obtained encoded data is transferred to the segment S-3, and the number S-3 of the segment S-3 is written in the segment information table. As described above, the quantized coefficients sequentially sent from the low-frequency components are Huffman-coded from one stage to the next stage by using one band Huffman coding unit 34, and the segment is selected by the segment selector 31. And the segment number is the segment information table 2
Written to 2.

In this way, the same progressive coding as that of the first embodiment can be realized. <Third Embodiment> Next, a third embodiment will be described.

FIG. 8 is a block diagram showing the construction of an image processing apparatus according to the third embodiment of the present invention. In the figure,
41 is a color conversion unit, 42 is a sub-sampling unit, and 43 is D
CT section, 55-57 are quantization sections, 58-60 are quantization tables corresponding to the quantization sections 55-57, 61-
63 is a Huffman code part, 50 is a Huffman table, 51
Is a segment selector, 52 is a segment information table, 53 is a compression memory, 65 is a CPU that controls the entire apparatus, and 66 is an R that stores data such as the program of FIG. 10 according to the flow chart for the CPU 65 to operate.
OM, 67 are RAMs used as work areas for various programs, and 68 is an adder. Again 7
Reference numeral 0 is a multi-stage quantizer / encoder, and the quantizers 55-55
57, quantization tables 58-60, Huffman coding unit 61
˜63, and a Huffman table 50.

A circuit having the same name as in FIG. 1 has the same function as that in FIG.

Next, the procedure for writing the encoded data in the compression memory 53 for each stage will be described.

DCT converted by the DCT unit 43
The coefficient is transferred to the multi-stage quantizing / encoding unit 70, and is quantized and encoded in multi-stages as shown below.

In the first stage, the DCT coefficient is quantized by the quantizer 55 for each color component (Y, U, V) for each block using the quantization table 58. The result is called a quantized coefficient and is encoded by the Huffman encoder 61. The encoded data is the segment S- of the compression memory 53 selected by the segment selector 51.
Forwarded to 1. Then, the number S-1 of the segment S-1 is written in the segment information table 52. The quantization error generated at that time, that is, the residual data A is sent to the quantization unit 56.

Next, in the second stage, the quantizer 56
The residual data A sent from the quantization unit 55 is quantized using the quantization table 59. The quantized coefficient obtained as a result is encoded by the Huffman encoder 62. The encoded data is transferred to the segment S-2 of the compression memory 53 selected by the segment selector 51.
Then, the number S-2 of the segment S-2 is written in the segment information table 52. Further, the quantization error generated at that time, that is, the residual data B is sent to the quantization unit 57.

Further, in the third stage, the quantizer 57 quantizes the residual data B sent from the quantizer 56 using the quantization table 60. The quantized coefficient obtained as a result is encoded by the Huffman encoding unit 63.
The encoded data is transferred to the segment S-3 of the compression memory 53 selected by the segment selector 51. Then, the number S-3 of the segment S-3 is written in the segment information table 52.

In the following, the encoded data in each stage is processed by the same procedure as in the first embodiment described above, and the compression memory 53 divided into a plurality of segments, the segment selector 51 for selecting the segment, and the information thereof. Fixed-length compression can be realized by using the saved segment information table 52.

Here, in the conventional method, since the quantization is performed in only one step, the deterioration of the information amount due to the quantization error becomes large. However, as in the third embodiment, the quantization is performed in multiple steps. By doing so, the amount of information deleted in the second and third steps is saved, so that the deterioration of the image quality can be largely prevented.

For the quantization in each stage, for example, a quantization table that preserves the information amount in the low frequency space is used in the first stage, and the information amount in the intermediate frequency space is preserved in the second stage. By using such a quantization table that preserves the amount of information in the high frequency space in the third stage, the property of quantization in each stage can be changed. Therefore, it is possible to apply variously to the image mainly including the space below the intermediate frequency depending on the purpose such as using up to the second stage.

Furthermore, by changing the quantization table at each stage, the amount of compressed data at each stage can be changed, and thereby more accurate fixed length compression can be realized. For example, when the compressed data amount of the first, second, and third stages is set to be 3: 2: 1, when the total compressed data amount is smaller than the target compressed data amount, the compressed data amount of all stages is set. Can be used, and when the compressed data amount exceeds about 10% of the target compressed data amount,
The target compressed data amount can be realized by deleting the compressed data in the third stage.

Regarding decompression of compressed data, the Huffman coding units 61 to 63 include three Huffman decoding units and a quantizing unit 5.
5 to 57, three inverse quantization units, quantization tables 58 to 60, three inverse quantization tables, DCT unit 43, an inverse DCT unit, and adder 68, an adder having the same configuration. , They may be provided so as to correspond to each other.

The operation in this case will be briefly described.

The segment selector 51 transfers each encoded data from the compression memory 53 to the three Huffman decoding units according to the segment information table 52.
The three Huffman decoding units decode the encoded data and transfer the decoded data to the three inverse quantization units. The three dequantization units dequantize the obtained quantized coefficients and transfer the dequantized coefficients to the adder. In this adder, the results of the three inverse quantizers are added to each color component for each pixel in the 8 × 8 block, and the inverse DCT is performed.
The process of transferring to the department is performed. The subsequent process is the same as that of the third embodiment.

In this way, compressed data can be expanded. <Fourth Embodiment> In the above-described first embodiment, the stage which is invalidated when all the compression memories are filled is invalidated from encoded data having a high frequency component, but the present invention is not limited to this. The present invention is not limited to this, and as in the fourth embodiment, coded data with a high frequency component or coded data with an intermediate frequency component may be adaptively selected and invalidated. <Fifth Embodiment> In the above-described first to fourth embodiments, four stages are provided in the progressive coding, but the present invention is not limited to this, and the gist of the present invention. The number of stages may be set to two or three, or five or more as long as it does not deviate from the above range. <Sixth Embodiment> In the first to fourth embodiments, the type shown in FIG. 5 is used as the segment information table, but the present invention is not limited to this, and the gist of the present invention is not limited to this. Various modifications can be made within the range that does not deviate.

An example of the segment information table other than that shown in FIG. 5 will be described below.

FIG. 9 is a diagram for explaining the segment information table according to the sixth embodiment.

The configuration of the entire apparatus is the same as that shown in FIG. 1 as an example.

In FIG. 9, a frame surrounded by a solid line corresponds to each segment of the compression memory 13, and a number in parentheses in the frame indicates a segment number. In addition, the stage number is shown in the left side region of the frame divided into two by the dotted line, and the order of the selected segment number of each stage is shown in the right side region.

Therefore, the segment S-1 is the segment selected as the first segment of the stage (1), segment S-.
2 is the first selected segment of stage (2), segment S-3 is the first selected segment of stage (3), and segment S-3 is the first selected segment of stage (3) Segment, segment S-
5 is the segment selected in the second stage of the stage (1), and if a segment is similarly selected thereafter,
The order of the selected stage number and the segment selected by that stage is written.

When the Nth (last) segment is selected and the coding is not completed, the stage (4) having the highest frequency component is invalidated, and the stage (4)
Segment S-4 in which the encoded data of
The encoded data of the other stages are written in S-11 and S-15. Therefore, the table of the segment S-4 has the stage (4) and the order of the selected segment numbers (1).
Is the stage (1) and the segment number order (a + 1) selected, and in the table of the segment S-11, the stage (4) and the segment number order (2) selected is the stage (2). Segment number order (a
+1), in the table of the segment S-15, the stage (4) and the selected segment number order (3) are the stage (1) and the selected segment number order (a +
2) can be rewritten respectively.

The difference between the segment information tables of FIG. 5 and FIG. 9 is that FIG. 9 requires less memory than the table of FIG. In the case of FIG. 5, this is because the END mark attached to the stage where encoding has been completed and the memory for writing the segment number initially assigned to the invalid stage increase the amount of data stored in the compression memory. This is because.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

As described above, according to the embodiment of the present invention, in the progressive coding, it is possible to realize the reduction of the scan time by the reduction of the number of scans, the deletion of the large capacity memory for one image, and the fixed length compression. ..

[0059]

As described above, according to the present invention, image data can be efficiently compressed and stored.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating zigzag scanning of quantized coefficients according to the first embodiment.

FIG. 3 is a diagram illustrating a progressive encoding step configuration and a quantized coefficient in the first embodiment.

FIG. 4 is a diagram illustrating the contents of a compression memory according to the first embodiment.

FIG. 5 is a diagram illustrating a segment information table for each stage according to the first embodiment.

FIG. 6 is a flow chart illustrating a compression process according to the first embodiment.

FIG. 7 is a block diagram showing a configuration of an image processing apparatus according to a second embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of an image processing apparatus according to a third embodiment of the present invention.

FIG. 9 is a diagram illustrating a segment information table according to a sixth embodiment.

[Explanation of symbols]

 1, 21, 41 Color conversion section 2, 22, 42 Sub-sampling section 3, 23, 43 DCT section 4, 24, 55-57 Quantization section 5, 25, 58-60 Quantization section table 6, 7, 8, 9,61-63 Huffman code part 10,50 Huffman table 11,31,51 Segment selector 12,32,52 Segment information table 13,33,53 Compression memory 14,36,65 CPU 15,37,66 ROM 16,38 , 67 RAM 34 band Huffman encoder

Claims (5)

[Claims] 1. The input frequency conversion data is encoded for each stage according to the frequency, and the encoded frequency conversion data of each stage is independently stored in a plurality of storage areas, and each stage and the storage area are stored. An image processing method, characterized in that the correspondence with is stored. 2. Storage means having a plurality of storage areas, encoding means for encoding input frequency conversion data for each quantization step according to frequency, and said storage means for each of said quantization steps in said plurality of storage areas. Writing means for writing the encoded data obtained by the encoding means, wherein the writing means is writing the first step of the quantization step for the first storage area among the plurality of storage areas, When the writing of the second step of the quantization step to the second storage area is completed, it is possible to write the remaining encoded data of the second step to the empty storage areas of the plurality of storage areas. Characteristic image processing device. 3. The image processing apparatus according to claim 2, wherein the encoding means performs Huffman encoding. 4. One step of the quantization step is invalidated when the total amount of encoded data obtained by the encoding means exceeds the storage capacity of the storage means and when the frequency component is the highest step. The image processing apparatus according to claim 2, wherein 5. The image processing apparatus according to claim 2, wherein the writing unit includes a management unit that manages a writing result in a table.