JPH0564004A - Picture communication equipment - Google Patents

Abstract

PURPOSE:To reduce the emphasis of a low frequency component accompanying the elimination of a high frequency component at the time of quantization for compressed encoding, and to improve the quality of a digitally communicated picture. CONSTITUTION:In equipment for communicating picture signals by compressed- encoding, the picture signal band-limited after passing through a filter 51 is orthogonally transformed by an orthogonal transforming part 52. Next, a coefficient value corresponding to the frequency component of the output of the orthogonal transforming part 52 is quantized by a quantizing part 53. The level of the quantized coefficient value is decided by a detecting part 54, and in the case that the output corresponding to the high frequency component exceeds a threshold, a control signal is formed, and the coefficient of the filter 51 is varied adaptively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image communication apparatus used by connecting to a digital line having a plurality of information channels and control signal channels, and more particularly to compression coding using orthogonal transform and quantization. And a pre-filter that can be adaptively varied so as to suppress the level and appearance of higher-order coefficients depending on the state of the transform coefficient as a result of the orthogonal transform.

[0002]

2. Description of the Related Art Advances in digital communication technology have led communication systems to build a common substrate for carrying various information such as voice, telephone, text, data and video. In particular, by changing the conventional analog communication type to digital communication type, it becomes possible to communicate still image and moving image information, and it is expected to be used as a videophone.

By the way, if an image is to be communicated, it is necessary to communicate in a limited band, so that information is compressed by encoding or the like. Orthogonal transformation, quantization, and variable length coding algorithms are available as compression coding methods adopted in conventional videophone devices. In this method, a coefficient in which energy is concentrated by orthogonal transformation is concentrated in a lower order by reducing higher-order components by quantization, and information is compressed by variable-length coding.

At this time, the image signal is digitized by sampling, but before and after the filtering process according to the sampling rate, it is unnecessary for the original image information such as a carrier wave in NTSC contained in the image signal. The components and the components such as aliasing in sampling are removed. In addition, depending on the application, there are some in which the pixel information can be changed by changing the pixel configuration by thinning out the pixels, that is, the transmission time can be changed.

[0005]

When processing information having a plurality of pixel configurations in the above-described filtering process at the time of compression encoding, a filter having suitable characteristics is prepared in advance according to the type of pixel configuration. The characteristics of this filter are fixed. In the case of an image type, for example, an image containing many high frequency components or a noise image, there is usually a tendency for the higher order components of the orthogonal transform coefficient to increase, and after passing this through a filter with fixed characteristics, the higher order components are quantized. Is removed, the low-order or low-frequency components contained in these unnecessary signals are emphasized and appear as new low-frequency noise, and the quality of the television image is impaired.

The present invention has been made in view of the problems of the above-mentioned conventional image communication apparatus, and provides an apparatus capable of performing band control filter processing suitable for image information.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the coefficients of the prefilter are adapted to suppress the generation of high frequency components when the number of high-order components of the orthogonal transform coefficient increases. The image communication apparatus is configured so that it can be varied dynamically.

[0008]

The image information excluding unnecessary frequency components is orthogonally transformed by the orthogonal transformation unit 52 in the filter unit 51 of FIG. 2, and the coefficient value corresponding to the output frequency component is quantized by the quantization unit 53. It After that, when the output corresponding to the high frequency component of the quantized coefficient value appears in the detection unit 54 at a large value exceeding a preset threshold value, the filter unit 51 is based on this information. Forming a signal 55 controlling
The control signal 55 adaptively changes the coefficient of the filter unit 51 to suppress the generation of high frequency components.

As a result, it is possible to reduce the information that is not originally contained in the image information and the noise due to the emphasis of the low frequency component due to the removal of the high frequency component by the quantization, and to reproduce a visually pleasing image.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, the entire videophone device will be described with reference to FIG. Reference numeral 1 denotes a line interface unit, to which a digital line 30 having a plurality of information channels B1 and B2 and a control signal channel D is connected,
The information channel and the control channel are demultiplexed. That is, the multiplexing process is performed when the information is output to the digital line 30, and the separation process is performed when the information is input from the digital line.

The information fetched from the line interface unit 1 and the information generated internally are stored in the system control unit 2
And is separated into audio information and image information.
The system control unit 2 controls all the functional units described below, and is designed to analyze the fetched information and the internally generated information and appropriately control each functional unit.

The image information separated by the system control unit 2 is a compression-encoded signal when taken in from the digital line, and is sent to the decoding unit 3 to be decoded. The decoded and restored image signal is temporarily stored in the display memory 7 via the image processing unit 5, and when the image signals for one screen are complete, the image processing unit 5 sends the image signal to the display control unit 6. , Which is transferred to the display unit 8 and displayed. A CRT, a liquid crystal display element, or the like is used as the display unit 8.

The input image from the internal camera 9 or the VTR 11 from the external video input terminal 13 or the external camera 1
Input images such as 2 are temporarily stored in the memory 14 by the image processing unit 5 via the input processing unit 10 and then sent from the image processing unit 5 to the encoding unit 4 again. The encoding unit 4 compression-encodes the image information according to the standardized method and sends it to the system control unit 2.

On the other hand, the voice signal separated by the system control unit 2 is decoded by the voice decoding unit 21, is stored in the temporary voice memory 19 by the voice processing unit 18, and is again analog signal by the voice processing unit 18. After being converted into a signal and subjected to appropriate signal processing, it is output to the handset 17. Handset 1
The audio signal input to 7 is digitized by the audio processing unit 18, temporarily stored in the audio memory 19, and then compressed / encoded by the audio encoding unit 20 via the audio processing unit 18 again. 2 is supplied.

The image information and audio information thus captured or processed are supplied to the system control unit 2 and multiplexed, and then sent from the line interface unit 1 to the digital line 30.

In the system controller 2, the call controller 22
The incoming / outgoing call information is output to or the information input from the operation unit 15 (such as input of a telephone number) is input to the operation interface unit 1.
It is taken into the system control unit 2 through 6, and is controlled so that each processing unit is processed based on the input information.

The image processing unit 5 of the videophone device having the above-described structure has a built-in structure for controlling filtering for signal compression as shown in FIG. That is, a filter unit 51 that outputs image information from which unnecessary frequency components have been removed from the input image signal, an orthogonal transform unit 52 that orthogonally transforms the output signal of the filter unit 51, and the orthogonal transform unit 52.
There is provided a quantizer 53 for quantizing a coefficient value corresponding to the frequency component output from, and a detector 54 for detecting a predetermined frequency component from the quantized coefficient value to form a control signal. The detection unit 54 detects whether or not the coefficient value corresponding to the high frequency component among the coefficient values quantized by the quantization unit 53 exceeds a predetermined level and is output, and when it exceeds the control level, the control signal 55. Is formed and is input to the filter unit 51. The filter unit 51 is formed of, for example, the digital filter shown in FIG. 3, and adaptively adjusts the filter coefficient Cij according to the content of the control signal 55 based on the detection result. By varying the filter coefficient Cij, a wider area is removed and the coefficient level of the high frequency component is suppressed.

The filter section 51 shown in FIG.
To the pixel P _{0, 0} to be determined, an example of a 2-dimensional filter to filter processing by weighting the levels of the neighboring 8 pixels and pixel horizontally and vertically as shown in FIG.

The image information quantized by the quantizer 53 is variable-length coded by the encoder 4 and subjected to desired compression, and then output to the system controller 2. In the above embodiment, the filter unit 51 incorporated in the image processing unit 5 is configured by using a two-dimensional digital filter capable of real-time processing, but the desired pixel level V ₀ , ₀ is stored in the memory in advance. From the neighboring pixel level, CPU (central processing unit) or DSP (digital signal processor)
It is also possible to calculate V ₀ , ₀ = ΣΣCij × Vij by using the above. It can also be realized by an analog filter before A / D conversion for digitizing image information.

[0020]

As described above, according to the present invention, not only is the filter changed depending on the type of pixel configuration,
Since the filter can be adaptively controlled according to the type of image or the signal, for example, by suppressing the high-order component of the orthogonal transform coefficient that occurs in the case of an image including many high frequency components or a noise image, There is an effect that new low frequency noise due to the emphasis of frequency components can be suppressed, an image that looks good can be obtained, and the quality of image communication can be significantly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a videophone device according to the present invention.

FIG. 2 is a block diagram showing a configuration of an image processing unit of the embodiment.

FIG. 3 is a block diagram showing a specific example of a filter unit of the same embodiment.

FIG. 4 is a pixel correlation diagram illustrating a calculation process of a filter unit.

[Explanation of symbols]

 1 line interface unit 2 system control unit 3 image decoding unit 4 image encoding unit 5 image processing unit 6 display control unit 7 display memory 8 display unit 9 internal camera 10 capture control unit 51 filter unit 52 orthogonal transform unit 53 quantization unit 54 detector 55 control signal

Claims (1)

[Claims] 1. A signal which is used by connecting to a digital line having a plurality of information channels and a control signal channel, compression-codes a digitized image signal, and decodes the compression-coded signal into an image signal. In an image communication apparatus including a processing circuit, compression coding means included in the signal processing circuit performs orthogonal transform, quantization and variable length coding on an image signal that has passed through a band limiting filter. An image communication apparatus comprising: a means and a means for determining a state of a coefficient of the orthogonal transformation and adaptively varying the band limiting filter.