Television – Bandwidth reduction system – Data rate reduction
Reexamination Certificate
1999-07-09
2002-09-03
Rao, Andy (Department: 2713)
Television
Bandwidth reduction system
Data rate reduction
C375S240010
Reexamination Certificate
active
06445418
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video coding and decoding method for an image communication system. Particularly, the present invention relates to a video coding and decoding method for setting a reference compression ratio for prevention of degradation of picture quality during video reconstruction, compressing a present image with change of the compression ratio in accordance with a transmission rate, comparing the compression ratio of the present compressed image with the reference compression ratio, controlling a compensation value of a video signal obtained before the compression to lower complexity of the video signal if the compression ratio of the present compressed image exceeds the reference compression ratio, and applying the compression ratio to the compensation value controlled image in coding video signals in an image communication system, thereby minimizing the degradation of transmitting image quality and increasing transmission efficiency.
2. Description of Related Art
FIG. 1
schematically illustrates a configuration of an image communication system according to a related art.
The image communication system allows the image and voice of a caller to be simultaneously transmitted through communication lines including cables, such as PSTN (Public Switched Telephone Network), dedicated lines and optical cable, and/or wireless networks.
Such image communication system comprises: a charge coupled device (CCD) 1 for converting images incoming through a lens
1
a
for taking a photograph into electronic video signals; a CCD driver
2
for driving the CCD
1
and processing the electronic video signals received from the CCD
1
to provide outputs; a digital signal processor
3
for digital signal processing the video signals output from the CCD driver
2
to output the signals through a monitor
4
and, simultaneously, transforming the video signals into a specified format (CCIR656 format) of luminance signals (Y) and color signals (Cb, Cr) for video compression; a video compression/reconstruction unit
5
for performing compression or reconstruction of the video signals incoming through the CCD
1
or transmission lines; a communication control and interface unit
6
for transmitting the compressed video signals or receiving video signals transmitted from another image communication system of the other party; and a controller
7
for controlling the overall circuit for the video signal processing, compression/reconstruction, and transmission.
The following description concerns the operation of the image communication system having such configuration.
Primarily, an image received through the lens
1
a
is converted into an electronic video signal in the CCD
1
and then input into the CCD driver
2
.
The CCD driver
2
then performs analog signal compensation with respect to the input video signal to provide a signal of a predetermined level to the digital signal processor
3
.
Subsequently, the digital signal processor
3
performs clamp, RGB color control, and brightness control with respect to the input video signal to display the photographed image through the monitor
4
.
At this time, the digital signal processor
3
transforms a luminance signal Y and a color signal Cb and Cr into a specified format for compression of transmitting image and provides the transformed signal to the video compression/reconstruction unit
5
.
Thereafter, the video compression/reconstruction unit
5
compresses the video signal received from the digital signal processor
3
according to JPEG (Joint Photographic Coding Experts Group) or MPEG (Moving Picture Experts Group). The compressed video signal is transmitted via the communication control and interface unit
6
over a communication line to another image communication system of the other party.
Alternatively, a video signal received via the communication control and interface unit
6
from the image communication system of the other party is respectively reconstructed and signal processed in the video compression/reconstruction unit
5
and the digital signal processor
3
and then displayed through the monitor
4
.
Such signal processing is controlled by the controller
7
.
This image communication system basically has a function of controlling a compression ratio of the photographed video signal to comport with a video data transmission rate which means the number of image frames per unit time (frames/second) required for the video transmission.
Techniques for video compression and transmission have usually been standardized. JPEG for still picture compression and MPEG for moving picture compression are typical image compression methods. These compression techniques use a quantization table.
However, in case of compressing an image using the quantization table, the file size of compressed video data becomes larger as the image gets more complicated, so the video data transmission is time-delayed and the number of image frames which can be transmitted for the unit time decreases.
Consequently, the quantization table should be controlled to increase the compression ratio and decrease the file size before the transmission for the purpose of satisfying the required number of image frames per unit time.
However, when such compressed file is reconstructed in the other party's system, an image of much degraded picture quality is displayed due to damage on the contour of the image (that is, an edge is not displayed in good order), block effect, or loss of reconstructed data which may be caused by over compression of the source image.
Briefly, the amount of data of a video signal to be compressed increases as the complexity of transmitting image gets larger. If the compression ratio is increased to deal with the large amount of data, the resultant compressed video signal is reconstructed to an image of degraded picture quality.
Particularly, in case of employing the NTSC (National Television System Committee) mode, several frames to 30 frames should be transmitted for a second. In this occasion, increase of compression ratio for a complex image may lead to a result quite different from a source image.
Besides, the conventional techniques perform contour compensation emphasizing edge components (high frequency components) of an image before compressing the image, so the contour compensated image is compressed, decreasing compression efficiency.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a video coding and decoding method for an image communication system that substantially obviates one or more of the limitations and disadvantages of the related art.
An objective of the present invention is to provide a video coding method for setting a reference compression ratio available for minimizing picture degradation, comparing a compression ratio of a present compressed image with the set reference compression ratio, and decreasing a complexity of a source image to control the present compression ratio to be smaller than the reference compression ratio if the present compression ratio exceeds the reference compression ratio in an image communication system, thereby minimizing degradation of picture quality when the image is received and reconstructed by another system.
Another objective of the present invention is to provide a video coding method for setting a video data transmission rate of a transmission line and a reference compression ratio for minimizing picture degradation, compressing a present image according to the transmission rate, comparing a present compression ratio of the compressed image with the reference compression ratio, and decreasing a complexity of a source image obtained before the compression to control the present compression ratio to be smaller than the reference compression ratio if the present compression ratio of the compressed image exceeds the reference compression ratio in an image communication system, thereby minimizing degradation of picture quality when the image is received and reconstructed by another system.
Still
Lee Byoung Ok
Oh Byong Khi
LG Electronics Inc.
Rao Andy
LandOfFree
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