Learned feature motion detection

1. A data processing device for detecting motion in a sequence of video frames each comprising one or more blocks of pixels, the data processing device comprising:

a sampling unit configured to determine image characteristics by point sampling at a set of sample points of a block;

a feature generation unit configured to form a current feature for the block in dependence on the determined image characteristics, the current feature being an image characteristic histogram having a plurality of values derived from the sample points in which each value of the plurality of values corresponds to a bin defining a predefined range and includes a count of the number of sampling points having an image characteristic falling within that bin; and

motion detection logic configured to generate a motion output for a block by comparing the current feature for the block to a learned feature representing historical feature values for the block, wherein the learned feature represents a historical image characteristic histogram for the block.

2. A data processing device as claimed in claim 1 , wherein each bin of the current feature has a corresponding bin in the learned feature having a historical value for the predefined range of that bin, and the historical value at each bin of the learned feature is a weighted average of the count of the number of sampling points having an image characteristic falling within that bin for the block over a plurality of frames.

3. A data processing device as claimed in claim 1 , wherein the sampling unit is configured to randomly generate the set of sample points of the block, the set of sample points being fixed for the block over the sequence of frames.

4. A data processing device as claimed in claim 1 , wherein the sampling unit is configured to randomly generate the set of sample points of the block according to a pseudo-random Halton sequence.

5. A data processing device as claimed in claim 1 , the data processing device further comprising decision logic configured to generate an indication of motion for a frame based on the one or more motion outputs generated by the motion detection logic in respect of the blocks of that frame.

6. A data processing device as claimed in claim 1 , wherein the feature generation unit is configured to maintain the learned feature of the block by, on receiving a frame of the sequence, decaying, according to a predefined decay factor, its plurality of values and allocating the values of the current feature to the corresponding values of the learned feature.

7. A data processing device as claimed in claim 6 , wherein the feature generation unit is configured to weight the values of the current feature according to a predefined weighting factor prior to allocating the values of the current feature to the values of the learned feature.

8. A data processing device as claimed in claim 1 , wherein the comparison performed by the motion detection logic comprises forming an estimate as to whether, based on a measure of differences between the values of the current feature and the corresponding values of the learned feature, and to within a predefined or adaptive threshold, the current feature is expected based on the historical values of the learned feature of the block.

9. A data processing device as claimed in claim 8 , wherein the motion detection logic is configured to generate the motion output so as to indicate motion at the block if the estimate exceeds the predefined or adaptive threshold.

10. A data processing device as claimed in claim 8 , wherein the motion detection logic is configured to maintain an estimate of an expected degree of variation of the block and, in dependence on that estimate, form the adaptive threshold for the block.

11. A data processing device as claimed in claim 10 , wherein the motion detection logic is configured to maintain the estimate of the expected degree of variation of the block by, on receiving a frame, updating the estimate in dependence on a measure of the similarity between the current feature formed for the block of the frame and the learned feature maintained for the block.

12. A data processing device as claimed in claim 1 , wherein the feature generation unit is configured to: compare the image characteristics of pairs of sample points of the set, each comparison being between the sample points of the respective pair; and form the current feature for the block such that each value represents the result of the comparison for a pair of sample points.

13. A data processing device as claimed in claim 12 , wherein the learned feature represents historical feature values for the pairs of sample points of the block, and each value of the current feature formed in respect of a pair of sample points has a corresponding value in the learned feature representing the historical value for that pair of sample points.

14. A data processing device as claimed in claim 12 , wherein each value of the current feature comprises a bit as a binary representation of the result of the comparison by the motion detection logic for the respective pair of sample points.

15. A data processing device as claimed in claim 12 , wherein the feature generation unit is configured to randomly select each pair of points from the set of sample points of the block.

16. A data processing device as claimed in claim 12 , wherein the feature generation unit is configured to, for each value of the current feature, represent the result of the comparison with a binary value indicating which of the image characteristics of the sample points of the pair is greater in value.

17. A data processing device as claimed in claim 12 , wherein the historical value at each of the values of the learned feature is a weighted average of the results of comparisons by the feature generation unit for the respective pair of sample points of the block over a plurality of frames.

18. A method of detecting motion in a sequence of video frames each comprising one or more blocks of pixels, the method comprising:

identifying image characteristics by point sampling at a set of sample points of a block;

forming a current feature for the block in dependence on the identified image characteristics, the current feature being an image characteristic histogram having a plurality of values derived from the sample points in which each value of the plurality of values corresponds to a bin defining a predefined range and includes a count of the number of sampling points having an image characteristic falling within that bin; and

generating a motion output for a block by comparing the current feature for the block to a learned feature having a plurality of values representing historical feature values for the block, wherein the learned feature represents a historical image characteristic histogram for the block.

19. A non-transitory computer readable storage medium having stored thereon a computer readable description of an integrated circuit that, when processed in an integrated circuit manufacturing system, causes the integrated circuit manufacturing system to manufacture a data processing device embodied in hardware on an integrated circuit, the data processing device for detecting motion in a sequence of video frames each comprising one or more blocks of pixels, the data processing device comprising:

a sampling unit configured to determine image characteristics by point sampling at a set of sample points of a block;

a feature generation unit configured to form a current feature for the block in dependence on the determined image characteristics, the current feature being an image characteristic histogram having a plurality of values derived from the sample points in which each value of the plurality of values corresponds to a bin defining a predefined range and includes a count of the number of sampling points having an image characteristic falling within that bin; and

motion detection logic configured to generate a motion output for a block by comparing the current feature for the block to a learned feature representing historical feature values for the block, wherein the learned feature represents a historical image characteristic histogram for the block.