Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Patent
1995-05-03
1997-02-18
Tran, Thai Q.
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
348398, 348438, 386109, 386112, H04N 979, H04N 576
Patent
active
056046022
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and a device for bit-rate reduction for the recording of images on a video recorder.
It applies in particular to the digital recording of an image but also to the transmission and storage of images.
2. Discussion of the Background
For the high definition digital television studios of the future it would appear to be essential to be able to record the high definition television signal in digital form in order to preserve the quality of the images in the course of the multiple reading recording operations which take place while editing recording tapes. The known analog high definition video recorders use magnetic tape reels and this recording medium could also be envisaged for digital video recorders. However, to allow convenient and reliable use, cassette-based video recorders would be better adapted. In fact, current technology would appear to be unsuited to these choices since, to obtain the high data throughput demanded by such a recording, it would be necessary to use a very large number, 8 or 16, of reading heads, and a magnetic tape and a recording method of much higher performance than those currently available. Other problems related to recording on cassette are related to the fact that the time available on a tape should exceed at least 60 minutes and that the recording of the sound should be carried out on at least four digital audio channels. To meet these requirements, digital solutions with signal bit-rate compression may naturally be envisaged while conforming with the main constraints related to the use of a digital video recorder. A first constraint is that a fixed bit rate per frame or per image must be employed so as to allow image-by-image editing and random access for the images on the recording tape. Random access to the images requires an image or a frame always to commence exactly synchronously with the instant of synchronization recorded on the tape, or otherwise searching and positioning will be impossible. Image-by-image editing requires the repositioned image to occupy the same space on the tape as the new image and also the images to be truly independent of one another. In accordance with a second constraint, the coding used must allow image reading in special modes such as "slow motion", "speeded up" and the "freeze-frame advance" mode. In the "slow motion" modes, reconstruction of the images must be perfect and in the "speeded up" modes it must be possible to recognize the images. It should be appreciated that for the currently existing cassette-based video recorders, in the "slow motion" modes the information read contains few errors on account of the techniques known as "overscanning" and "tracking", slow motion can be obtained by repeating frames or by interpolation. In the "fast forward" modes, however, owing to the position of the reading heads relative to the tape, only a part of the information is read (the remainder is interpolated). Moreover, for one and the same image, some lines originate from the image at the instant t and others from the image at instants t+1, t+2, . . . , depending on the reading speed. Finally, in accordance with a third constraint, for professional applications it is imperative to guarantee quality of reconstruction without visible degradation of the image even after a coding/decoding series.
Most of the existing bit-rate reduction techniques were developed for transmission applications. They are generally based on splitting the image by cosine (or sub-band) transform followed by variable-length coding. The mean bit rate is fixed, although the bit rate can vary from one image to another. Moreover, to obtain high compression rates these techniques employ inter-image coding with motion compensation so that the images depend on the previous images.
For recording applications, the main problem is of keeping a fixed bit rate per image or image zone (per sector recorded for example) while using techniques adaptable to the contents of the image, these tech
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L. Vandendorpe, Optimized Quantization for Image Subband Coding, Signal Processing: Image Communication 4, pp. 65-79 Nov. 1991.
Guillotel Philippe
Tourtier Philippe
"Thomson-CSF"
Lee Y.
Tran Thai Q.
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