Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1990-03-20
1992-03-17
Peng, John K.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358105, 358136, 358141, H04N 712, H04N 704, H04N o718
Patent
active
050973304
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a high definition television transmission system, in which the image is divided into a plurality of parts, for each one of which a video data transmission mode is selected from among at least two modes which differ from one another by the sampling structure, and to a high definition television receiver to represent images transmitted by such a system, in which the image is divided into a plurality of parts, for each one of which a video data reproduction mode is determined from among at least two modes on the basis of an indication received from the transmitter in digital form.
The invention is applicable to the system referred to as DATV (Digitally Assisted Television), in which data complementary to the video data are transmitted by digital means. The purpose of such a system is to reduce the pass band of the video channel.
A system of this type is known from the paper entitled "Motion compensated interpolation applied to HD. MAC pictures encoding and decoding" by M. R. Haghiri and F. Fonsalas, presented at the "2nd International workshop on signal processing of HDTV", L'Aquila, Feb. 29-Mar. 1988.
SUMMARY OF THE INVENTION
In the proposed system, the signal to be transmitted is generated by a 50 Hz camera with interlaced image of 1152 lines with 1440 pixels per line. This signal is assumed to be sampled at 54 MHz; this is four times the frequency indicated in the recommendation 601 of the CCIR. The purpose of the encoding is to reduce the pass band of the transmitted signal by a factor of 4, with an associated digital data throughput which is as small as possible. To this end, the image is divided into a plurality of parts, in this case squares of 16.times.16 pixels, and use is made, for each part, of a transmission mode selected from among three, each one of these modes being characterized by the range of speeds (of the movements in the image) to which it is applicable, and by the duration of transmission of a complete image. An "80 millisecond" mode exhibits an image frequency of 12.5 Hz and is applicable to the virtually fixed image parts. A "40 millisecond" mode exhibits an image frequency of 25 Hz and is applicable to speeds extending as far as a far pixels per image. A "20 millisecond" mode exhibits an image frequency of 50 Hz and is applicable to the image parts where the objects have the highest speeds.
Moreover, in the 40 ms mode, a speed vector is transmitted, this being valid for the image part considered, which permits the receiver to create an intermediate image between two effectively received images.
If consideration is given only to the "40 ms" and "20 ms" modes, the first (40 ms) mode corresponds to the determination and to the transmission, via a digital channel of a speed vector for each one of the image parts, while in the second (20 ms) mode the image frequency is higher than in the first mode but with a lower spatial definition. Moreover, data for defining the selection effected for each of said parts are transmitted over the digital channel.
The determination and the transmission of a speed vector permit the use of the 40 ms mode for higher maximum speeds. As a result of this, the number of bits required to transmit the value of the local speed is greater, and this transmission consumes a significant part of the digital transmission capacity, and may even exceed it. In order to reduce the digital throughput, the transmission system according to the invention advantageously comprises means for determining, for a complete image, in the set of speed vectors, a subset containing the vectors which are encountered most frequently in this image, means for digitally transmitting the definition of all the vectors of this subset, each speed vector being defined by referring to the subset, and means for selecting, for each part of the image, either the first mode if the speed vector of the image part to be transmitted is an element of the subset, or the second mode if the speed vector of the image part to be transmitted is not an
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"Television Motion Measurement for Data and Other Applications"; Thomas; Research Department Report, BBC, Sep. 1987, pp. 1-20.
Guichard Philippe
Haghiri Mohammad-Reza
Marion Michael E.
Peng John K.
U.S. Philips Corporation
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