JP2558996B2 - Image coding method and image coding apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding method and an image coding apparatus used for compressing and coding a digital image signal for transmission or recording.

[0002]

2. Description of the Related Art In recent years, digital image signals have been compressed and encoded for transmission or recording. When an image signal is transmitted, compression coding is performed at a compression rate according to the transmission rate of the communication path, and a higher quality image can be transmitted as the transmission rate increases. In addition, when the image signal is recorded on a recording medium having a limited recording capacity, the recording time is shortened in order to compress and encode the image signal at a compression rate according to the recording time and to record an image with high image quality. By increasing the encoding, recording can be performed for a long time, but the image quality deteriorates.

[0003]

However, it is necessary to change the coding compression rate according to the transmission rate of the transmission line or the recording time of the recording medium, and it is necessary to perform the encoding suitable for the coding compression rate. Had challenges.
When the coding compression rate is increased, the coding noise in the high frequency component of the image signal becomes noticeable and becomes noticeable to the human eye. Therefore, the high frequency component of the image signal is attenuated in advance and the band is limited before the coding process. I don't care about coding noise.

However, even if the high-quality image is obtained by lowering the encoding compression rate, the encoded reproduced image becomes a low-quality image having no high-frequency component. Further, if the band limitation of the image signal is performed uniformly over the entire image, the entire image becomes blurred and the image quality deteriorates.

In view of the above points, the present invention realizes a highly efficient coding process by performing band limitation suitable for the coding compression rate, and by performing band limitation considering the local characteristics of the image. An object is to provide an image encoding method and an image encoding device.

[0006]

The image coding apparatus according to the present invention includes a band limiting processing means for performing a band limiting process on an image signal according to an encoding compression rate, and a band limiting process . In front of the image signal
And an encoding means for performing compression encoding processing at the encoding compression rate.
And a band limiting processing means.
Divides the image signal into blocks of multiple pixels
Blocking circuit and a pixel included in the block
Pixel level change measurement time to measure pixel level change
And the magnitude of the pixel level change amount of the block and
Depending on the encoding compression rate, the image signal is transmitted in multiple modes.
Mode signal generation to generate mode signal for band limiting
Circuit and the image signal in block units in the mode
It is composed of a band limiting circuit for band limiting .

[0007]

Further, the change pixel level change amount of the block of interest, and the pixel level change amount of the plurality of peripheral blocks in the neighborhood of the current block, and a mode for band-limiting said current block according to the coding compression rate The device limits the band of the target block such that the difference between the mode of limiting the band of the target block and the mode of limiting the band of the peripheral block falls within a predetermined range.

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

As a result, the band limitation suitable for the coding compression rate is performed, the coding noise of the high frequency component in the coding at the high compression rate is reduced, and the image quality of the reproduced image can be improved, and the low compression rate is achieved. Even in the encoding, it is possible to obtain a reproduced image of high quality without losing the delicacy of the original image.

By changing the mode of band limitation depending on the image area, the band can be limited without losing the delicacy of the entire image, and the band limitation mode of the target image area and the image areas around it. By keeping the difference with the band limitation mode of within the predetermined range,
It is possible to suppress a rapid change in the band limiting mode and reduce the image quality deterioration due to the band limiting.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image encoding method and an image encoding apparatus according to the present invention will be described below in detail with reference to the drawings.

First, a first embodiment of the image coding apparatus of the present invention will be described with reference to FIG. FIG. 1 shows an image coding apparatus including a band limiting processing means 1, a compression coding processing means 2, and a compression rate control signal generator 3. FIG.
The image coding apparatus of (1) switches between the standard image quality mode and the high image quality mode according to the compression ratio control signal generated by the compression ratio control signal generator 3, and limits the band of the image signal according to this mode to perform coding. It controls the compression rate.

In FIG. 1, the band limiting processing means 1 band-limits image signals input in different modes according to the compression rate control signal generated from the compression rate control signal generator 3. Bandwidth to limit when encoding at high compression rate,
By increasing the bandwidth and the amount to be limited, the image signal is more strongly band-limited, and is weakly band-limited or not band-limited at the time of encoding at a low compression rate. The compression encoding means 2 performs compression encoding processing on the image signal band-limited by the band limitation processing means 1 at a compression rate according to the compression rate control signal.

As described above, the present embodiment can realize the band limitation according to the compression rate and can reduce the image quality deterioration due to the coding noise of the reproduced image even if the coding is performed at the high compression rate.

If the band limitation is realized by a low-pass filtering circuit that cuts off high-frequency components of the image signal, the coding noise becomes unnoticeable even when the coding is performed at a high compression rate, and the quality of the reproduced image deteriorates. Can be reduced.

Next, a second embodiment of the image coding apparatus of the present invention will be described with reference to FIG. FIG. 2 shows an example of the band limiting means 1 described in the first embodiment, which includes a blocking circuit 4, a pixel level change amount measuring circuit 5, a mode signal generating circuit 6, and a band limiting circuit 7. Is.

First, the image signal is divided into blocks made up of a plurality of pixels by the blocking circuit 4. Next, the pixel level change amount of the obtained block is calculated by the pixel level change amount measuring circuit 5, and the pixel level change amount of the block is input to the mode signal generating circuit 6. The mode signal generation circuit 6 selects a mode for band limitation in block units according to the amount of pixel level variation of a block and the coding compression rate, and outputs a band limitation mode signal. The band limiting mode signal is input to the band limiting circuit 7, and the band limiting circuit 7 band limits the block in a mode according to the band limiting mode signal.

The band limiting means 1 performs stronger band limiting when the coding compression rate is high, while weakly limiting the band when the coding compression rate is low, or does not perform band limiting at all. As a result, the image signal is sent to the compression encoding means 2 without losing the delicacy of the original image signal. In addition, instead of performing band limitation on the entire image, the mode of band limitation is changed in block units, and stronger band limitation is applied to blocks with higher pixel level changes that require more information in compression encoding. By doing
It is possible to reduce the occurrence of coding noise due to a decrease in the amount of information, and it is possible to realize efficient compression coding.

Next, a third embodiment of the image coding apparatus of the present invention will be described with reference to FIG. Although the block diagram of the band limiting means is almost the same as that of FIG. 2, the mode signal generating circuit 8 shown in FIG. 3 has a pixel level change amount of a target block and a plurality of peripheral blocks around the target block. A band limiting mode signal is selected according to the pixel level change amount and the encoding compression rate, and a band limiting mode signal is output. The band limiting mode signal is input to the band limiting circuit 9, and the band limiting circuit 9 limits the band of the target block in the mode selected by the mode signal generating circuit 8.

Although the band limiting mode is selected in accordance with the pixel level change amount of the target block and the coding compression rate, it is the same as in the second embodiment described above. When the mode in which the peripheral blocks around the target block are band-limited is extremely different, the discontinuity may adversely affect the image quality. Therefore, the band limiting mode of the target block is selected according to the pixel level change amount of the target block and the pixel level change amount of the peripheral block so that the band limiting mode of the target block and the band limiting mode of the peripheral block do not change abruptly. This makes it possible to suppress image quality deterioration due to band limitation.

Since it suffices that the band limiting mode does not change suddenly, the configuration is not limited to that shown in FIG.
It can also be realized by adding the mode signal correction circuit 10 to the band limiting means of FIG. 2 as shown in FIG. The circuit of FIG. 4 corrects the band limiting mode signal of the target block generated by the mode signal generating circuit 6 of FIG. 2 by the band limiting mode signals of a plurality of peripheral blocks around the target block, and the band limiting mode abruptly changes. Control change. The band of the target block is limited by the band limiting circuit 11 according to the corrected band limiting mode signal. As a result, it is possible to limit the band without causing image quality deterioration,
It is possible to realize more efficient compression encoding.

Further, the band limiting means in the above-mentioned first, second and third embodiments can be realized by a low-pass filtering type circuit that cuts off high-frequency components, but the present invention is not limited to this, and the original image signal Bandwidth may be limited so as to remove noise components. It is known that a noise removal circuit that removes noise components can be obtained by performing band limitation according to the amplitude level of an image signal. This is often realized by a low-pass filter having a non-linear characteristic that cuts off high-frequency components as the amplitude level decreases.

The band limiting process may be performed in the spatial direction within one image or in the time axis direction between a plurality of images, or in both the space direction and the time axis direction.

The band limiting mode may be any number as long as it is two or more modes. Further, the compression coding means may be coding using orthogonal transformation, or may be any one as long as it compresses and codes the image signal.

The description of the image coding method of the present invention is as follows.
Exactly the same as the description of the image encoding device, a method of compressing and encoding an image signal at a plurality of encoding compression rates,
By performing band limitation processing on the image signal in a plurality of modes according to the encoding compression rate when performing compression encoding processing,
It is possible to realize an efficient image coding method.

[0033]

As described above, the present invention is suitable for the coding compression rate by performing the band limitation processing of the image signal in a plurality of modes according to the coding compression rate when performing the compression coding processing. Bandwidth is limited, coding noise of high frequency components in high compression rate coding can be reduced and the quality of the reproduced image can be improved, and the delicacy of the original image is lost even in low compression rate coding. Without this, it is possible to obtain a reproduced image of high quality.

Further, by changing the mode of band limitation depending on the image area, the band can be limited without losing the delicacy of the entire image, and the band limitation mode of the target image area and the image areas around it. By keeping the difference with the band limitation mode of within the predetermined range,
It is possible to suppress a rapid change in the band limiting mode and reduce the image quality deterioration due to the band limiting.

[Brief description of drawings]

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

FIG. 2 is a block diagram of band limiting means according to a second embodiment of the present invention.

FIG. 3 is a block diagram of means for selecting a band limiting mode according to a third embodiment of the present invention.

FIG. 4 is a block diagram of means for correcting a band limitation mode according to a third embodiment of the present invention.

[Explanation of symbols]

 1 band limiting means 2 compression encoding means 3 compression rate control signal generator 4 blocking circuit 5 pixel level variation measuring circuit 6 mode signal generating circuit 7 band limiting circuit 8 mode signal generating circuit 9 band limiting circuit 10 mode signal correcting circuit 11 Band limiting circuit

Claims (7)

(57) [Claims] 1. A band limitation processing means for performing a band limitation process on an image signal according to a coding compression ratio, and the band limited image.
Coding for compressing and coding an image signal at the coding compression ratio
An image coding and means, said band limiting processing means includes a blocking circuit for dividing the block consisting of the image signals from a plurality of pixels, the change amount of the pixel levels of the pixels included in the block a pixel level change amount measuring circuit for measuring a pixel level of the block
Depending on the magnitude of the amount of change and the coding compression ratio, a plurality of modes
A mode signal generation circuit for generating a mode signal for that band-limits the image signal by de, the image signal in the mode
Image encoding apparatus characterized in that it is constituted by a band limiting circuit for band-limiting block units Nos. 2. The mode signal generating circuit compresses an image signal.
The amount of change in pixel level of the target block to be encoded, the encoding compression rate, and the surroundings of the target block.
A plurality of generating a mode signal for band-limiting said current block according to the pixel level variation in the size of the surrounding blocks that
The image coding apparatus according to claim 1, characterized in that the. 3. The band limitation processing means is a compression code of an image signal.
The band limiting mode of the target block of interest to be processed No. of claim 1, wherein further comprising a mode signal correction circuit for correcting in accordance with the band limiting mode of a plurality of peripheral blocks in the neighborhood of the current block Image encoding device. 4. The high frequency component of the image signal
The image coding apparatus according to any one of claims 1, 2 or 3, characterized in that band-limited so as to block. 5. A method for compression- encoding an image signal, the image signal being divided into blocks each composed of a plurality of pixels,
Measures the pixel level change amount of the pixels included in the block
However, depending on the magnitude of the pixel level change amount and the coding compression ratio,
In the same way, band limiting processing of the image signal is performed in multiple modes.
Compress the band-limited image signal at the encoding compression ratio
Image coding method, characterized in that the coding process. 6. A mode for band-limiting operations on a <br/> Ru target blocks to be processed compression coding of the image signal, band limiting processing of a plurality of peripheral blocks in the neighborhood of the current block
A band limiting process is performed on the target block such that a difference between the target block and the target mode is within a predetermined range.
5. The image coding method according to item 5 . 7. The band limiting process according to claim 5, wherein band limiting processing is performed so as to block high frequency components of the image signal.
An image coding method described in any of the above.