Television – Bandwidth reduction system – Data rate reduction
Patent
1996-06-21
1998-10-13
Chin, Tommy P.
Television
Bandwidth reduction system
Data rate reduction
348699, H04N 712
Patent
active
058220070
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and to an apparatus for motion estimation using block matching.
BACKGROUND
Block matching is well known as a robust and intuitively simple method of motion estimation for television pictures.
FIG. 7 shows a possible architecture for a one-sided block matching motion estimator with a range of .+-.2 pixels per field horizontally and vertically, to integer accuracy. This architecture is based on processing elements, one per candidate motion vector. Each processing element PE accumulates the errors between the pixels (which form a group related to a candidate block position and vector, respectively) arriving at its two inputs, storing partial results in order to arrive at a total error for each block. The processing elements are connected together by means not shown in the figure in order to find which one yields the minimum error for each block. The processing elements may calculate the minimum absolute value or the minimum squared error.
In the one-sided motion estimator in FIG. 7, all the processing elements PE have a common input INP, corresponding to the current block. The relative displacements between the pixels in the search window are provided by a network of line LD and sample SD delays that follow the field delay FD connected to input INP.
U.S. Pat. No. 5,162,907 shows one-sided block matching, in which the reference picture is not the picture to be interpolated. However, when the purpose of the motion estimation is to provide accurate interpolation between images, for example in a 50 Hz to 100 Hz upconverter, conventional block matching suffers from the problem that the blocks are situated in the original fields rather than in the fields to be interpolated, leading to possible errors in the calculated motion field.
SUMMARY
It is one object of the invention to disclose a method of block matching, which overcomes this problem.
It is a further object of the invention to disclose an apparatus which utilizes the inventive method.
The invention uses two-sided block matching. The advantages of two-sided block matching are not confined to 50 Hz to 100 Hz upconversion but apply to any temporal interpolation, for example 50 Hz to 60 Hz or 50 Hz to 75 Hz standards conversion, for which motion vectors are required at points in time between input fields.
In a conventional, or `one-sided`, block matching, one possible architecture in FIG. 1, the current field (or frame) CF of the picture is divided into blocks, typically rectangular. For each current block CB, a search is made among overlapping blocks of the same size in the previous field (or frame) PF to find one that matches the current-field block CB best, usually using a mean-square or mean-absolute error criterion summed across the pixels in the block. The relative position of the best-matching block in the previous frame gives the chosen displacement, or motion, vector MV for the current block. For a given current block CB, the set of pixels involved in the previous frame is known as the search window SW corresponding to that block. Thus, the block matching process makes use of the current block and the search window.
The problem with one-sided block matching, when applied to field rate upconversion, is that the blocks for which motion vectors are sought lie in the input fields rather than in the fields IF to be interpolated. This leads to a positional error PE (with respect to the position PCB of the current block) in FIG. 2 in the information used to estimate the motion vector, which increases with the speed of motion. This error becomes more important when block matching is applied to localizing. the boundaries between moving areas, as described in EP93 402188 of the applicant.
The positional error PE can be corrected by displacing the block in the interpolated field IF appropriately according to the motion vectors, but this leads to the occurrence of gaps GP (areas in the interpolated field for which no motion vectors exist) and, equally, of areas CT for which two or more motion vectors conflict, as show
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Bolender Nadine
Hackett Andrew
Kerdranvat Michael
Knee Michael
Chin Tommy P.
Lee Y.
Thomson Multimedia S.A.
Tripoli Joseph S.
Wein Frederick A.
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