JP2506402B2 - Orthogonal transform coding device and orthogonal inverse transform decoding device for video signal - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal transform coding method for video signals, and more particularly to a device for orthogonally transforming and coding a video signal subjected to field interlace scanning, and a data coded as such. The present invention relates to an apparatus that decodes and orthogonally inversely transforms to form a video signal.

BACKGROUND ART For example, when storing an image signal picked up by a solid-state image pickup device such as a CCD in a storage device such as a memory card or a magnetic disk, consider the capacity of the storage device and compress the image signal data to a small amount. is necessary. like this,
Orthogonal transform coding is known as a method of compressing image data.

This method is as follows. First, the image represented by the image signal is divided into a predetermined number of blocks, and the data of each pixel in each divided block is orthogonally transformed.

In the image signal, the low frequency component occupies a large power component. On the other hand, the high-frequency component is not significant in terms of power, but is significant in terms of information. Also, the characteristics for these are visually different. Therefore, the image signal is orthogonally transformed from such low frequency components to high frequency components,
Quantization suitable for each component is performed and encoded. On the receiving or reproducing side, the encoded signal is inversely transformed to obtain the original signal. In this way, efficient encoding can be performed.

In the orthogonal transform coding, the entire screen is divided into a plurality of blocks with an appropriate number of pixels as one block, and a numerical sequence of sample values is orthogonally transformed for each of these blocks. That is, linear conversion is performed with mutually independent conversion axes that match the characteristics of the original image signal. As a result, the transformed terms are more independent, ie, more uncorrelated, than the original sampled values. This suppresses redundant information. This method is, so to speak, an operation on the frequency axis.

As a result, power is concentrated on a specific component due to the statistical properties of the image signal. Therefore, many bits are allocated to the low-frequency component of high power, and the high-frequency component of low power is roughly quantized with a small number of bits, while considering the visual characteristics. This can reduce the number of bits per block.

By performing such orthogonal transformation and encoding, it is possible to reduce the capacity of the storage device as compared with the case where the data of the pixels forming the image signal are directly quantized and stored.

By the way, the field interlaced scanning video signal for interlacing two fields to form one frame is 1
Looking at a frame as a unit, even if such orthogonal transformation and coding are performed, the redundancy is still large. This is because such a pair of fields has a strong correlation of image data, and if these are directly subjected to orthogonal transformation and encoded,
This is because it simply requires a storage capacity twice as large as the image data storage area for one field.

An object of the present invention is to provide an orthogonal transform coding apparatus and an orthogonal inverse transform decoding apparatus for a video signal, which solves the above-mentioned drawbacks of the prior art and enables efficient data compression even for a video signal interlaced and scanned. The purpose is to do.

DISCLOSURE OF THE INVENTION According to the present invention, the interlace-scanned frame video signal is optimally encoded for the feature that the correlation between the images of the first and second fields represented by it is strong. More specifically, when the image data of one field, for example, the second field is encoded, the data compression is performed by taking the difference from the other field, that is, the first field. As a result, the image data can be recorded or transmitted with a smaller data amount as compared with the case of directly encoding the frame image data.

An orthogonal transform coding apparatus for video signals according to the present invention includes first storage means for storing image data representing a pair of interlaced fields, and a screen represented by the image data stored in the first storage means. Is divided into blocks, and the block forming means for extracting the image data for each block, the orthogonal transforming means for orthogonally transforming the image data of the extracted blocks to form the transform coefficient data, and 1 of the transform coefficient data.
A difference means for taking a difference between a pair of fields and forming difference data representing the difference, and an encoding means for encoding the transform coefficient data of one field of the transform coefficient data with a larger number of bits for lower frequency components. And a first output means for outputting the encoded transform coefficient data and the encoded difference data.

The orthogonal inverse transform decoding device for video signals according to the present invention is
Third storage means for accumulating data obtained from the first output means, decoding means for decoding the data of the third storage means for each block, and addition means for adding the decoded transform coefficient data to the difference data. Then, the decoded transform coefficient data is orthogonally inversely transformed for each block into image data of one field, and the added result data is orthogonally inversely transformed for each block to obtain image data of the other field. And conversion means.

Description of Embodiments Next, an orthogonal transform coding method of a video signal according to the present invention will be described in detail with reference to the accompanying drawings.

Referring first to FIG. 5, an embodiment of an orthogonal transform coding apparatus for video signals according to the present invention has a video signal source 10 such as a solid-state image pickup device, which is connected via an analog-digital converter (ADC) 12. Connected to bus 14. The video signal source 10 is a signal source that forms a frame video signal subjected to field-interlaced scanning in the form of an analog signal in the present embodiment, and is not an image pickup device, but a receiving circuit for receiving such a signal from a communication line, for example. May be The analog / digital converter 12 is a signal conversion circuit that converts such an analog video signal into corresponding digital data.

The present apparatus is an orthogonal transform coding apparatus that orthogonally transforms and codes such a frame video signal and stores it in the image recording memory 16, for example. The image recording memory 16 is, for example,
A storage device such as an IC memory or a magnetic disk is advantageously applied. For example, in the case of an IC memory, it may be fixedly mounted inside the apparatus, but may be in the form of a card or a cartridge detachably connected to the apparatus by the connector 17.

In this apparatus, the image represented by the image data is divided into blocks of a predetermined size, the data of each pixel in each divided block is orthogonally transformed, quantized, and encoded.
At this time, when encoding the image data of one field, for example, the second field, which constitutes the interlaced-scanned frame, the difference from the other field, that is, the first field is taken. This encoding method is optimal for the feature that the images of the first and second fields represented by the frame video signal have a strong correlation between the two. by this,
Image data can be recorded or transmitted with a smaller amount of data than in the case of directly encoding frame image data.

This data compression function is realized by temporarily storing the image data obtained from the video signal source 10 in the memory 18, calculating it in the memory 18, and processing it. memory
Reference numeral 18 denotes a main storage area functioning as a work area therefor, and such processing is configured to be performed by a central processing unit (CPU) 22 according to a processing program.

The image data compressed in the memory 18 in this way may be stored in the image recording memory 16, and may be stored in the transmitter.
It may be transmitted from 24 to the line 26. The image recording memory 16 and the transmitter 24 may both be provided, or either one may be provided.

The data compression processing in this embodiment will be described in more detail with reference to FIG. First, the frame video signal output from the video signal source 10 is converted into an analog / digital converter 12
Are converted into corresponding digital data at. This is a bus
It is transferred from 14 to the memory 18 and is temporarily stored therein. This frame image data is composed of first and second field data 30a and 30b.

First, the data 30a of the first field is read out and the functional unit 32a extracts the block. More specifically, the image represented by the image data, which may be considered as a frame or a field, is divided into blocks of a predetermined size. That is, the entire rectangular screen 60 is divided into a plurality of square areas, that is, blocks 62a, 62b, ..., 62h, etc., as shown in FIG. 7, in the data compression processing. Each of these square areas has, for example, 16 pixels in the horizontal direction Y (FIG. 7) of the screen and X in the vertical direction.
Although it has 16 pixels, it may be a rectangle different from this. The block extraction function unit 32a extracts the data of each pixel which is included in the first field data 30a and constitutes a specific block, for example, 62a, and provides it to the orthogonal transformation function unit 34a. The state of the pixel data is illustrated in FIG. 8A.
The block extraction function unit 32a sequentially performs this block extraction for all blocks in the first field 30a.

The specific block thus extracted, for example, the image data 46a of 62a is orthogonally transformed by the orthogonal transformation function unit 34a. In this embodiment, the orthogonal transform 34a is advantageously a cosine transform, which transforms the image data into frequency domain data. FIG. 8B shows an example of data in an orthogonally transformed state. The cosine transform has few conversion errors and is suitable for compression of image data.

Similarly, the data 30b of the second field is also read from the memory 18, and the functional unit 32b extracts the block. This reading and block extraction 32b are preferably performed in synchronization with those in the first field. If done synchronously, the data compression of the first and second fields can be done simultaneously. If the data is not synchronized, the first field data is read and the block is extracted in addition to the first field data compression process when the second field data is compressed.

In any case, the data 30b of the second field is the first
Similar to the field, block extraction 32b is performed and orthogonal transformation 34b is performed. The block extraction 32b of the second field 30a is performed for the same block as that of the first field 30a, 62a in this example. The state of the pixel data of the extracted block 62a of the second field is illustrated in FIG. 8C, which generally corresponds to that of the first field (8B.
(Figure) is almost the same. After that, this block extraction 32
The b and the orthogonal transformation 34b are sequentially performed for all blocks of the second field 30b in synchronization with those of the first field 30a. In this way, the image data 30a and 30b of the first and second fields are converted into frequency domain data for each block such as 62a, 62b, ... 62h and stored in the memory 18.

The transform coefficient data 40a that has been orthogonally transformed in the first field 34a is first encoded by the encoding function unit 36a. This encoding is also performed for each block such as 62a, 62b, ... 62h. In the present embodiment, the coding method is such that the transform coefficient data to be coded is truncated to an appropriate threshold value, and the remaining transform coefficient data has a large number of bits in a low frequency component and a high frequency component, that is, an analog / digital converter.
The frequency component closer to the 12 sampling frequencies is assigned a smaller number of bits. In the encoding function unit 36a,
Orthogonal transform data 40a with such coded bit allocation
Is quantized.

Since the distribution of the transform coefficient data generally differs depending on the picture pattern of the image represented by the video signal, adaptive coding in which the threshold value is variable according to the variance of the transform coefficient data is advantageously applied. That is, in the case of a pattern in which the gradation change is small, the frequency of the low frequency component is extremely high, so it is preferable to allocate a large number of bits to the low frequency component and set the threshold value high. The fine pattern is the opposite.

On the other hand, for the second field, the transform coefficient data 40b transformed by the orthogonal transform 34b is the transform coefficient data of the block corresponding to the first field in the difference function unit 38.
The difference 42 with respect to 40a is extracted. That is, the orthogonal transformation 34a
The second-field transform coefficient data 40b similarly orthogonally transformed to the respective frequency component values 64a (FIG. 8B) included in the first-field transform coefficient data 40a.
The difference 42 between the corresponding frequency component values 64b (Fig. 8C) included in
Is obtained in the functional unit 38. The extraction of the difference is sequentially performed for all frequency component values included in one block, for example, 62a. The state of the difference data is illustrated in FIG. 8D. After that, perform this operation in the corresponding blocks of both fields.
62b, …… Repeat every 62h.

This difference data 42 is the encoding function unit 36b in this embodiment.
Is encoded in. This encoding may also be adaptive.

Thus, the first encoded 36a for each block 62a, etc.
The field data 42a and the encoded difference data 42b are completed in the memory 18. These encoded data 42a and 42b completed in the memory 18 are read out according to an instruction from the CPU 22, transferred to the image recording memory 16 and accumulated therein, or transmitted to the transmission line 26 by the transmitter 24. To do.

Further, as shown in FIG. 2, in another embodiment of the present invention,
The differential data 42 may be directly output 16/24 together with the encoded data 42a of the first field without being encoded. In the other drawings showing other embodiments of the present invention, elements similar to those shown in FIG. 1 are designated by the same reference numerals.

As described above, according to these embodiments, the interlace-scanned frame video signal has a strong correlation between the images of the first and second fields represented, and one of the fields, for example, the first field, is noted. Data compression is performed by orthogonally transforming and encoding the field as it is, and taking the difference between the other field, that is, the second field in this example, with the first field. Therefore, the image data can be recorded or transmitted, that is, output with a smaller data amount than in the case of directly encoding the frame image data.

As can be seen from FIG. 8D, the difference data subjected to the orthogonal transformation 34b has almost no DC component and the high frequency region is almost occupied by noise. Generally, the first
Significant values are distributed in the frequency domain, which represents the difference between the patterns of the field and the second field. This region generally takes the intermediate frequency region. Therefore, in the coding 36b, a certain number of bits are allocated in a specific intermediate frequency region, and other coding bits are not particularly allocated to the DC component.

Referring to FIG. 3, another embodiment of the present invention is configured to take the difference 44 between the first and second fields after block extraction 32a and 32b and before performing orthogonal transforms 34a and 34b. There is. In this embodiment, grayscale data 46a and 46b of the first and second fields 30a and 30b.
Is calculated for each block 62a. The gradation data 46a of the first field is directly subjected to the orthogonal transformation 34a and the encoding 26a as in the other embodiments.

However, with respect to the data 30b of the second field, after the block extraction 32b, the difference function unit 44 obtains the difference data 48 for the gradation data 46a of the first field.
The orthogonal transform function unit 34b orthogonally transforms the difference data 48, and the encoding unit encodes the difference data thus orthogonally transformed. This encoding 36b may also be adaptive encoding, and the encoding 36b may not be performed.

The image data recorded in the image recording memory 16 or sent to the communication line 26 in this manner is reproduced as an original video signal by the orthogonal inverse transform decoding device having the configuration shown in FIG. The orthogonal inverse transform decoding device reads the image data compressed in the image recording memory 16 and receives the image data from the communication line 26 by the receiver 70, and decodes the image data to perform inverse orthogonal transform. Has a function of restoring the original video signal and reproducing it in the utilization device 72. The hardware configuration thereof may be the same as that of the orthogonal transform encoding device shown in FIG. 5, that is, the same device may have both a recording function and a reproducing function. However, in this embodiment,
The orthogonal inverse transform decoding device is configured as a device separate from the orthogonal transform encoding device.

The image recording memory 16 in which the image data compressed by the orthogonal transform encoding device is recorded usually takes the form of a storage device such as an IC memory or a magnetic disk. For example, in the case of an IC memory card or cartridge, the connector 74 is used. Is detachably connected to this device. When the image recording memory 16 is, for example, a magnetic disk, the magnetic disk is set in the magnetic disk reader. Further, when the image data is transmitted from the orthogonal transform encoding device through the communication line 16, the image data is received by the receiver 70.

The data reproducing function of the present apparatus is realized by temporarily accumulating the image data obtained from the image recording memory 16 or the communication line 26 in the memory 76, and calculating and processing it in the memory 76. The memory 76 constitutes a main storage area as a work area therefor, and the CPU 80 performs such processing according to a processing program. The image data reproduced in the memory 76 is output as an analog video signal to the utilization device 72 through a digital-analog converter (DAC) 82 in accordance with an instruction from the CPU 80. It should be noted that the connection function of the image recording memory 16, that is, the connector 74 and the receiver 70 may both be provided, or either one may be provided.

The data reproducing process in this embodiment will be described in more detail with reference to FIG. First, the data-compressed image data 86 read from the image memory 16 or received by the receiver 70 over the line 26, referred to herein as encoded data for convenience, is transferred from the bus 84 to the memory 76. , Once accumulated in this.

First, the encoded data 86 is the data of the first field.
88a and difference data 88b are contained in blocks 62a, 62b, ..., 62h.
Etc. are read out and are decoded by the functional units 90a and 90b, respectively. This decoding process is the reverse process of the process performed on the image data by the encoding function units 36a and 36b of the orthogonal transform encoding device, and is performed according to the decoding rule of the same method as those encoding rules. Of course, when the "encoded" data obtained in the embodiment described with reference to FIG. 2 is reproduced, the differential data is not "encoded" in the narrow sense, and therefore such differential data is decoded. It is directly output to the addition function unit 92 without passing through the function unit 90b. Here, "encoding in a narrow sense" refers to performing quantization by performing bit allocation suitable for the property of image data.

The compressed data of the first field is restored to the frequency domain data 96a for each block by the decoding function unit 90a and is supplied to the orthogonal inverse transform 94a. This inverse transformation 94a is applied to each block 62a,
62b …… Sequentially every 62h. On the other hand, the difference data 96b decoded by the decoding function unit 90b is the block 62
a, 62b …… 62h, etc. are given to the addition function unit 92,
In each block, for example, 62a, the corresponding frequency component value 64a included in the transform coefficient data 96a of the first field is added. The thus-added data 98 is passed to the orthogonal inverse transform function section 94b as the second field transform coefficient data. This completes the conversion output 64b of the second field of the block 62a.

The orthogonal inverse transform function unit 94a performs orthogonal inverse transform on the decoded transform coefficient data 96a of the first field. Orthogonal inverse transform 9
In this way, 4a has all the blocks 62a, 62b,
……, 62h, etc. will be sequentially performed. by this,
The gradation data 100a of the first field is completed in the memory 76. That is, the gradation data shown in FIG. 8A is completed. Similarly, the orthogonal inverse transform function unit 94b performs orthogonal inverse transform on the decoded transform coefficient data 98 of the second field in all blocks 62a, 62b, ...
, 62h, etc. are sequentially carried out and stored in the memory 76 as the gradation data 100b of the second field. This orthogonal inverse transform
94a and 94b are orthogonal transform function units of the orthogonal transform encoder.
This is the inverse process of the orthogonal transform performed on the image data in 34a and 34b, and is performed according to the inverse transform rule of the same method as those transform rules.

In this way, the image data 100a and 100b of the first and second fields completed in the memory 76 are sequentially read by the digital-analog converter 82 by the field interlace scanning method in accordance with the instruction from the CPU 80. The converter 82 converts this into a corresponding analog signal and outputs it to the utilization device 72. The utilization device 72 is a video reproduction device including a video monitor device such as a CRT and an image printer, for example. In this way, the analog video signal is reproduced by the utilization device. When outputting to the video monitor, it is preferable to output the first and second fields by the interlaced scanning method.

Although the embodiment in which the present invention is applied to the orthogonal transformation has been described, the present invention is not limited to this, and for example, predictive coding,
It is also effectively applied to other coding methods such as Hadamard transform and Fourier transform.

Effect According to the present invention, the image data of one field of the interlace-scanned frame video signal is compressed, and when encoding the image data of the other field, the difference from the one field is taken. By
Data is being compressed. As a result, the image data can be recorded or transmitted with a smaller data amount as compared with the case of directly encoding the frame image data.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a configuration of a data compression process in a video signal orthogonal transform coding device according to the present invention, and FIGS. 2 and 3 are other embodiments of the orthogonal transform coding device. Fig. 4 is a functional block diagram showing an example, Fig. 4 is a functional block diagram showing a configuration of data reproduction processing in a video signal orthogonal inverse transform decoding device according to the present invention, and Fig. 5 is a video signal orthogonal transform coding device according to the present invention. FIG. 6 is a block diagram showing an embodiment, FIG. 6 is a block diagram showing an embodiment of a video signal orthogonal inverse transform decoding device according to the present invention, and FIG. 7 is an explanatory diagram showing an example of screen block extraction in the embodiment. 8A to 8D are explanatory views showing an example of the data compression processing in the same embodiment. Explanation of code of main part 16 …… Image recording memory 18,76 …… Memory 32a …… Block extraction function part 34a …… Orthogonal transformation function part 36a …… Encoding function part 38, 44 …… Difference function part 90a …… Decoding function unit 92 …… Addition function unit 94a …… Orthogonal inverse transformation function unit

Claims (5)

(57) [Claims] 1. A first storage means for storing image data representing an interlaced first field and a second field, and the first and second field images stored in the first storage means. A screen represented by data is divided into blocks, and a pair of blocking means for extracting the image data for each block, and image data of the extracted blocks are orthogonally transformed to transform the first field and the second field. A pair of orthogonal transforming means for forming coefficient data, a first field of transform coefficient data respectively output from the pair of orthogonal transforming means, and a second field next to the first field.
Difference means for taking the difference from the conversion coefficient data of the field and forming difference data representing the difference, and the conversion coefficient of either one of the first field and the second field respectively output from the pair of orthogonal transform means. A first output means for outputting the encoded transform coefficient data and the encoded difference data; Is a video signal orthogonal transformation coding apparatus, which includes a connection unit to which a second storage unit that stores the coded data is connected. 2. The orthogonal transform according to claim 1, wherein the encoding means encodes the difference data, and the first output means outputs the encoded difference data. Encoding device. 3. The third storage means for accumulating the data obtained from the first output means of the apparatus according to claim 1, and the conversion coefficient data of the data in the third storage means for each block. Decoding means for decoding the conversion coefficient data decoded by the decoding means to the difference data of the data in the third storage means, and the conversion coefficient data decoded by the decoding means. A pair of orthogonal inverse transforms in which each block is subjected to orthogonal inverse transform to obtain the image data of the one field, and the added result data is subjected to orthogonal inverse transform in each block to obtain the image data of the other field. An orthogonal inverse transform decoding apparatus for video signals, comprising: 4. A third storage means for accumulating the coded data obtained from the first output means of the apparatus according to claim 2, and the data of the third storage means for each block. A pair of decoding means for decoding, addition means for adding the difference data decoded by the other of the decoding means to the conversion coefficient data of the data decoded by one of the decoding means, and the decoded conversion coefficient Data is orthogonally inversely transformed for each block to be image data of the one field,
The data resulting from the addition is inversely orthogonally transformed for each block to obtain the image data of the other field 1
An orthogonal inverse transform decoding apparatus for a video signal, comprising a pair of orthogonal inverse transform means. 5. The orthogonal inverse transform decoding device according to claim 3 or 4, wherein the device outputs the image data of the first and second fields subjected to the orthogonal inverse transform as a video signal of interlaced scanning. An orthogonal inverse transform signal device comprising a second output means.