JP2659635B2 - Image communication device - 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 communication apparatus used by being connected to a digital line having a plurality of information channels and a control signal channel, and more particularly to compression coding using orthogonal transform and quantization. A videophone device comprising a filter and adaptively changing a pre-filter so as to suppress the level and appearance of higher-order coefficients depending on the state of transform coefficients as a result of orthogonal transform.

[0002]

2. Description of the Related Art Advances in digital communication technology have led communication systems to build a common substrate for transmitting a variety of information, such as text, data and video, from telephones for voice. In particular, telephones have been changed from conventional analog communication systems to digital communication systems, so that still image and moving image video information can be communicated, and their use as videophones is expected.

[0003] When an image is to be communicated, it is necessary to communicate in a limited band, so that information is compressed by coding or the like. As a compression coding technique used in a conventional videophone device, there are orthogonal transform, quantization, and a variable length coding algorithm. In this method, a coefficient in which energy is concentrated by orthogonal transform is reduced to a higher order by quantization to reduce a higher order component, and information compression is performed by variable length coding.

At this time, the image signal is digitized by sampling, but before and after that, by performing a filtering process according to the sampling rate, unnecessary image information such as a carrier wave in NTSC included in the image signal is unnecessary. Components and components such as aliasing in sampling are removed. In some applications, the pixel configuration can be changed by pixel thinning or the like to change the amount of image information, that is, the transmission time can be changed.

[0005]

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

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

[0007]

In order to solve the above-mentioned problems, according to the present invention, when the number of higher-order components of the orthogonal transform coefficients increases, the coefficients of the pre-filter are adapted to suppress the generation of high-frequency components. The image communication device is configured to be able to dynamically change.

[0008]

The image information from which unnecessary frequency components have been removed by the filter unit 51 in FIG. 2 is orthogonally transformed by the orthogonal transformation unit 52, and the coefficient value corresponding to the output frequency component is quantized by the quantization unit 53. You. Thereafter, if the output corresponding to the high-frequency component of the quantized coefficient value appears as a large value exceeding a preset threshold value in the detection unit 54, the filter unit 51 Forming a signal 55 that controls
The coefficient of the filter unit 51 is adaptively varied by the control signal 55 to suppress generation of high frequency components.

As a result, noise that is not present in the original image information and noise due to emphasis of low-frequency components by removing high-frequency components by quantization can be reduced, and a visually beautiful image can be reproduced.

[0010]

DETAILED 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,
Demultiplexing of the information channel and the control channel is performed. That is, multiplex processing is performed when information is output to the digital line 30, and separation processing is performed when information is input from the digital line.

The information fetched from the line interface unit 1 and the internally generated information are transmitted to the system control unit 2.
To be separated into audio information, image information, and the like.
The system control unit 2 controls all the function units described below, is designed to analyze the information taken in and the information generated internally, and to appropriately control each function unit.

The image information separated by the system control unit 2 is a signal which has been compressed and coded in a state taken in from a digital line, so that it is sent to the decoding unit 3 for decoding. The decoded and restored image signal is temporarily stored in the display memory 7 via the image processing unit 5, and when the image signal for one screen is completed, the image processing unit 5 sends the image signal to the display control unit 6. Are transferred to the display unit 8 for display. As the display unit 8, a CRT, a liquid crystal display element, or the like is used.

An input image from the internal camera 9 or a VTR 11 or the external camera 1 from the external video input terminal 13
An input image such as 2 is temporarily stored in the memory 14 by the image processing unit 5 via the input processing unit 10 and then sent to the encoding unit 4 from the image processing unit 5 again. The encoding unit 4 compresses and encodes the image information according to a standardization method, and sends it to the system control unit 2.

On the other hand, the audio signal separated by the system control unit 2 is decoded by an audio decoding unit 21, temporarily stored in an audio memory 19 by an audio processing unit 18, and again converted into an analog signal by the audio processing unit 18. , And after appropriate signal processing, is output to the handset 17. Handset 1
The audio signal input to 7 is digitized by an audio processing unit 18, temporarily stored in an audio memory 19, again passed through the audio processing unit 18, compressed and encoded by an audio encoding unit 20, and then transmitted to a system control unit. 2 is supplied.

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

The system control unit 2 also includes a call control unit 22
Information (such as input of a telephone number) input from the operation unit 15 to the operation interface unit 1
6, the system control unit 2 is controlled to process each processing unit based on the input information.

The image processing unit 5 of the videophone device having the above-described configuration has a configuration for controlling filtering for signal compression as shown in FIG. That is, a filter unit 51 that outputs image information from an input image signal by removing unnecessary frequency components, an orthogonal transformation unit 52 that orthogonally transforms an output signal of the filter unit 51, and an orthogonal transformation unit 52
And a detector 54 for quantizing a coefficient value corresponding to the frequency component output from the controller and detecting a predetermined frequency component from the quantized coefficient value to form a control signal. The detecting unit 54 detects whether or not a coefficient value corresponding to a high-frequency component among the coefficient values quantized by the quantizing unit 53 is output beyond a predetermined level. Is formed and input to the filter unit 51. The filter unit 51 is composed of, for example, the digital filter shown in FIG. 3, and adaptively adjusts the filter coefficient Cij based on the content of the control signal 55 based on the detection result. By changing the filter coefficient Cij, a wider range is removed, and the coefficient level of the high frequency component is suppressed.

The filter unit 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 quantization unit 53 is subjected to variable-length encoding by the encoding unit 4, subjected to a desired compression, and output to the system control unit 2. In the above embodiment, the filter unit 51 built in the image processing section 5 is formed by using a two-dimensional digital filter capable of real-time processing, a level V _{0, 0} pixels determined, has been stored in advance in the memory CPU (Central Processing Unit) or DSP (Digital Signal Processor) from neighboring pixel levels
It can also be determined by computing the V _{0, 0} = ΣΣCij × Vij using like. Further, it can 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 the change of the filter depending on the type of the pixel structure,
Since the filter can be adaptively controlled according to the type of image or according to the signal, low-order components of orthogonal transform coefficients generated in the case of an image containing many high-frequency components or a noise image can be reduced, for example. New low-frequency noise due to the emphasis of the frequency component can be suppressed, and a clear image can be obtained, which has the effect of significantly improving the quality of image communication.

[Brief description of the drawings]

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

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

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

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

[Explanation of symbols]

 Reference Signs List 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 transformation unit 53 quantization unit 54 Detector 55 Control signal

Claims (1)

(57) [Claims] 1. A digital line having a plurality of information channels and a control signal channel is used for compression encoding of a digitized image signal and decoding the compression encoded signal into an image signal. In an image communication device including a signal processing circuit, a compression encoding unit included in the signal processing circuit performs orthogonal transform, quantization, and variable-length encoding on an image signal that has passed a filter that limits a band. means for applying, the coefficient to determine the state of the coefficients of the orthogonal transform
When it indicates that there are many high-frequency components,
Coefficient of the above band limiting filter so as to suppress the occurrence of
Means for changing the image quality.