Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
  • H04N19/51—Motion estimation or motion compensation

Definitions

• This invention relates to video processing and particularly to motion compensation of video processes.
• the present invention consists in one aspect in a method of video processing comprising the steps of identifying a motion vector for each of a plurality of overlapping picture blocks, picture shifting in accordance with said motion vectors to provide multiple shifted pictures and combining said multiple shifted pictures.
• the multiple shifted pictures are combined with respective weightings derived from the proximity of the associated pixel to the respective blocks.
• each pixel lies in four overlapping blocks.
• the major difference between a typical motion compensated system and a system according to one form of this invention is that, while a motion compensated system has a vector bandwidth similar to the pixel rate; the motion assisted system may have many fewer vectors per field. Each vector can be associated with a relatively large block.
• the resulting images may look very "blocky" or like independent tiles rather one image.
• the technique used in one form of this invention to avoid this effect is to construct each point as a mix of four images, which are constructed using the four closest block vectors. The relative distance from the four block centres controls the proportions in which the four images are mixed.
• the present invention consists in another aspect in a method of video processing comprising the steps of identifying a picture region, combining pixels in a first direction over that region; and performing a one dimensional correlation process upon said combined pixels to identify a motion vector in a second, orthogonal direction.
• the method further comprises the steps of combining pixels in said second direction over that region; and performing a one dimensional correlation process upon said combined pixels to identify a motion vector in said first direction.
• each individual frame of the sequence is split into a number of blocks.
• Each m by n block is then summed in one dimension to produce either an m by 1 or a 1 by n block.
• These two blocks are then analysed for motion in one dimension using phase correlation.
• Figure 1 is a block diagram of apparatus according to an embodiment of the present invention
• Figure 2 is a diagram illustrating the block structure and mix weightings.
• FIG. 3 is a diagram of apparatus according to another embodiment of the invention.
• Figure 4 is a diagram illustrating a further embodiment of the invention.
• H2 hpos(p(+,+) + (1 -hpos)p(-,+)
• the input video signal is taken to a block based motion estimator (100).
• This derives one vector for each block, N vectors per field, utilising phase correlation or simpler motion measurement techniques, which are held in a vector store (102).
• Figure 2 shows by way of example an image which has 20 measurement blocks arranged on a 5 x 4 grid with the block centres marked "X". It should be noted that the measurement blocks may be overlapping.
• the vectors vec(-,-), vec(+,-), vec(-,+) and vec(+,+) are then passed from the store (102) to picture shifters (104).
• P( + .-). and P( + . + ) are then mixed via blocks 106, 108 and 110 in a two-stage mixing process, first using hpos, and then mixing the two remaining signals using vpos. This produces output picture p(out).
• the picture shifts can be regarded as read/write operations with an offset determined by the vector. This offset may be employed on either the read or the write side. Forward or backward vectors can be employed, or combinations thereof.
• Each of the picture shifters shown in Figure 1 may comprise a vertical shifter followed by a horizontal shifter. It is not uncommon for horizontal motion to occur more frequently in the pictures to be processed than vertical motion. In this case a saving in hardware complexity may be achieved by reducing the number of vertical shift circuits.
• Figure 3 shows an example where only two vertical shifters are used. Because there are fewer vertical shifters, the vertical vector field is subsampled horizontally so as to make the number of required shift values correspond to the number of shifters. For example the four vectors of Figure 2 could be processed as shown below to obtain two vertical shift values and four horizontal shift values.
• V(-,-), and vec(+,-) have horizontal component H(+,-), and vertical component V(+,-), etc. Then:
• Horizontal Shift 2 H(+,-)
• Horizontal Shift 3 H(-,+)
• the use of these six shift values is shown in Figure 3.
• the input picture (30) is fed in parallel to two vertical shifters (31) (32).
• the four vectors from the blocks containing the current pixel are processed as described above in the vector processor (33) so as to derive respective vertical shift values for the two vertical shifters.
• the shifted output picture from the vertical shifter (31) is fed in parallel to two horizontal shifters (34) (35).
• These shifters are fed with horizontal shift values from the vector processor (33) in order to create the pictures p(-,-) and p(+,-) for the mixer shown in Figure 1.
• the output of the vertical shifter (32) is processed in a similar way in the horizontal shifters (36) and (37) to create the other two pictures for the mixer.
• the output picture mixer has been processed in accordance with motion vectors from four overlapping blocks, but the vertical component of the vectors have been used with reduced resolution to achieve a saving in hardware complexity. Where horizontal motion predominates the subjective quality of the pictures is not adversely affected.
• an input video signal is first organised (400) into b blocks; each block is n pixels by m lines. In one example, there are 63 blocks of 64 x 64 points. These are summed vertically to produce 63 blocks of 64 points. The blocks are 100% overlapping.
• the horizontal and vertical vectors may be used separately or alternatively combined vectorally before use.
• the post correlation filtering is optional and is used to increase the reliability of resulting vectors.
• adjacent blocks are filtered in the H ,V and temporal direction.
• the windowing and summing functions could be replaced by other means for combining pixels in one direction. It is preferable to take steps to remove block edge effects and it may sometimes be preferable to weight the sum or other combination to give priority to pixels close to the block centre.
• phase correlation is a particularly useful technique, other and perhaps simpler forms of correlation could alternatively be employed, such as block matching.
• a gradient approach could also be employed.
• Processing according to the present invention lends itself particularly well to software implementation or implementation in generic or video-specific digital signal processors.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Television Systems (AREA)
• Compression Or Coding Systems Of Tv Signals (AREA)

Applications Claiming Priority (5)

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• 2001
  • 2001-03-26 AU AU42585/01A patent/AU4258501A/en not_active Abandoned
  • 2001-03-26 JP JP2001575727A patent/JP2003530790A/ja active Pending
  • 2001-03-26 EP EP01915494A patent/EP1273176A2/de not_active Withdrawn
  • 2001-03-26 WO PCT/GB2001/001328 patent/WO2001078403A2/en not_active Ceased
  • 2001-03-26 CA CA002404655A patent/CA2404655A1/en not_active Abandoned

Non-Patent Citations (1)

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