Television – Format conversion
Patent
1996-03-27
1998-12-01
Kostak, Victor R.
Television
Format conversion
348427, H04N 701
Patent
active
058446168
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and to an apparatus for motion compensated interpolation.
BACKGROUND
For motion compensated interpolation (MCI) with sub-pixel accuracy the missing pixels need to be generated or interpolated prior to the motion compensation. For the Barcelona Olympic Games THOMSON HDMAC receivers have been built. Such receivers fulfil the preliminary HDMAC specification of the BRD (bandwidth restoration decoder) chip set for the Olympic Receiver Project/Version 2.1, Philips. The required pixel values are stored using line and pixel delays. A switch matrix selects such stored pixels which are currently needed for the processing. In order to avoid sub-pixel MCI, the interpolation is carried out prior to the motion compensation. Thus, the input data rate of the motion compensation circuitry is twice then that of the interpolation circuitry. The resulting hardware complexity is high. Sub-pixel interpolation does mean interpolation of pixels located between available samples.
INVENTION
It is one object of the invention to disclose a method of combined motion compensation and interpolation having a sub-pixel precision, but using only a limited number of pixels accessed by the switch matrix. This object is reached by the method disclosed in claim 1.
It is a further object of the invention to disclose an apparatus which utilises the inventive method. This object is reached by the apparatus disclosed in claim 8.
The invention leads to a reduced amount of stored data for performing a sub-pixel MCI using a simple switch matrix, only. A special arrangement of delays storing pixel values needed for the processing is used to extend the existing delay array. Because an increased number of pixels involved is used, an improved sub-pixel MCI is achieved. This is possible due to the fact that such delay extension does not affect significantly the decoded picture quality even if adjacent motion vectors do not match exactly to the current motion vector. The invention can be used in every system making use of MCI, especially in decoders of coding systems based on spatio-temporal subsampling and motion compensation. Motion compensation and interpolation are achieved simultaneously at the clock frequency of the input data stream. Therefore, the amount of data to process and the resulting hardware complexity are lower than in the cited prior art. The switch matrix is connected to line and pixel delays storing a window of a frame (or field) at time t from which a MCI is achieved to build a frame (or field) at time (t+/-T) by random access depending on motion vectors. T is a multiple of the frame (field) period. The number of pixels extracted by the switch matrix at each clock period is limited by hardware complexity constraints. The invention is based on the hypothesis that two consecutive sets of switch matrix outputs are juxtaposed or intersected. So, several consecutive sets of switch matrix outputs can be stored in order to carry out an interpolation using all available pixels. The hypothesis has been validated by investigating the behaviour on very critical source materials. The invention can be used in every system using motion compensation. Especially, it is suited to coding/decoding systems based on spatio-temporal subsampling and motion compensation like HDMAC.
In HDMAC this technique can be performed directly on sub-sampled fields. For each current pair of pixels (denoted 80-1 and 80-2) to be interpolated six samples come out of the switch matrix. In fact, only four samples are dedicated to the interpolation of one of these pixels, but two samples of the 2*4 samples are common. Therefore, only six switch matrix outputs are required. Due to the inventive delay extension at the output of the switch matrix the interpolation filter can use an input window of ten pixels for calculating an output pixel value (80.sub.-- 1 or 80.sub.-- 2). The vertical dimension of the interpolation filter is given by the number of different lines accessed by the switch matrix, e.g. three. The horizontal dimension
REFERENCES:
patent: 4587556 (1986-05-01), Collins
patent: 4654876 (1987-03-01), Atkins
patent: 5070403 (1991-12-01), Wilkinson
Collet Eric
Kerdranvat Michel
Kostak Victor R.
Thomson Multimedia S.A.
Tripoli Joseph S.
Wein Frederick A.
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