Determining a quality measure for a processed video signal

1. A method of determining a quality measure for a processed video signal generated from an original video signal, the method comprising:

determining a statistical metric for a value for a set of pixels of the original video signal;

determining the statistical metric for the value for a corresponding set of pixels of the processed video signal;

comparing the statistical metric for the original video signal with the statistical metric for the processed video signal to determine a quality measure for the processed video signal that approximates a peak signal-to-noise ratio of the processed video signal;

determining a level of clipping for the set of pixels of the original video signal having a luminance value that falls outside a clipping value range;

determining a level of clipping for the corresponding set of pixels of the processed video signal having a luminance value that falls outside the clipping value range;

calculating a difference between the determined level of clipping between the original video signal and the determined level of clipping between the processed video signal; and

modifying the quality measure for the processed video signal using the calculated difference between the respective levels of clipping for the original video signal and the processed video signal.

2. A method as claimed in claim 1 , wherein the statistical metric for the value for the set of pixels of the original video signal and the processed video signal is a standard deviation of the value for the respective set of pixels.

3. A method as claimed in claim 1 , wherein the value for a pixel is the luminance of the pixel.

4. A method as claimed in claim 3 , further comprising determining the quality measure using a predetermined function that relates the statistical metrics to values for the peak signal-to-noise ratio.

5. A method as claimed in claim 1 , further comprising modifying the quality measure for the processed video signal using a measure indicative of a number of distinct values in the set of pixels of the original video signal and/or the processed video signal.

6. A method as claimed in claim 5 , wherein the measure is an entropy of the value for the set of pixels of the original video signal and/or the processed video signal.

7. A method as claimed in claim 1 , wherein the set of pixels corresponds to a region of an image of the original video signal and processed video signal.

8. A method as claimed in claim 7 , further comprising:

determining the quality measure for a plurality of regions of the original video signal and the processed video signal, and

determining the quality measure by comparing the statistical metrics for the original video signal and the processed video signal for each region.

9. A method as claimed in claim 1 , further comprising determining an average quality measure from an average of the quality measures for a predetermined time period.

10. A method as claimed in claim 1 , further comprising adding the determined statistical metric to fingerprint data for the original video signal and/or processed video signal.

11. A video signal fingerprint generator for use in a method as claimed in claim 1 , configured to:

receive an input video signal;

determine a statistical metric for a value for a set of pixels of the video signal; and

output fingerprint data for the input video signal;

wherein the fingerprint data includes the determined statistical metric for the input video signal.

12. A video signal quality measure determiner for use in a method as claimed in claim 1 , configured to:

receive a statistical metric for a value for a set of pixels of an original video signal;

receive the statistical metric for the value for a corresponding set of pixels of a processed video signal; and

determine the quality measure for the processed video signal by comparing the statistical metrics for the original video signal and the processed video signal.

13. A method as claimed in claim 1 , wherein the determining of the level of clipping for the set of pixels of the original and the processed video signals comprises determining a portion of the respective sets of pixels having the luminance value that falls outside the clipping value range.

14. A system for determining a quality measure for a processed video signal generated from an original video signal, comprising:

a first video signal fingerprint generator configured to receive the original video signal as an input video signal and output fingerprint data for the input video signal that includes a statistical metric for a value for a set of pixels of the original video signal and a level of clipping for the set of pixels of the original video signal that have a luminance value that falls outside a clipping value range;

a second video signal fingerprint generator configured to receive the processed video signal as an input video signal and output fingerprint data for the input video signal that includes a statistical metric for a value for a set of pixels of the processed video signal and a level of clipping for the set of pixels of the processed video signal that have a luminance value that falls outside a clipping value range; and

a video signal quality measure determiner configured to:

receive the fingerprint data output by the first and second video signal fingerprint generators;

receive the statistical metric for the value for the set of pixels of the original video signal;

receive the statistical metric for the value for the corresponding set of pixels of the processed video signal;

compare the statistical metric for the original video signal with the statistical metric for the processed video signal to determine a quality measure for the processed video signal that approximates a peak signal-to-noise ratio of the processed video signal;

obtain, from the fingerprint data received from the first video signal fingerprint generator, the level of clipping for the set of pixels of the original video signal having the luminance value that falls outside a clipping value range;

obtain, from the fingerprint data received from the second video signal fingerprint generator, the level of clipping for the corresponding set of pixels of the processed video signal having the luminance value that falls outside the clipping value range;

calculate a difference between the determined level of clipping of the original video signal and the determined level of clipping of the processed video signal, and

modify the quality measure for the processed video signal using the calculated difference between the respective levels of clipping for the original video signal and the processed video signal.

15. The system as claimed in claim 14 , wherein the statistical metric for the value for the set of pixels of the original video signal and the processed video signal is a standard deviation of the value for the respective set of pixels.

16. The system as claimed in claim 14 , wherein the value for a pixel is the luminance of the pixel.

17. The system as claimed in claim 16 , wherein the video signal quality measure determiner is further configured to determine the quality measure using a predetermined function that relates the statistical metrics to values for the peak signal-to-noise ratio.

18. The system as claimed in claim 14 , wherein the video signal quality measure determiner is further configured to modify the quality measure for the processed video signal using a received measure indicative of a number of distinct values in the set of pixels of the original video signal and/or the processed video signal.

19. The system as claimed in claim 18 , wherein the measure is an entropy of the value for the set of pixels of the original video signal and/or the processed video signal.

20. The system as claimed in claim 14 ,

wherein the set of pixels corresponds to a region of an image of the original video signal and processed video signal, and

wherein the video signal quality measure determiner is further configured to:

determine the quality measure for a plurality of regions of the original video signal and processed video signal, and

determine the quality measure by comparing the statistical metrics for the original video signal and the processed video signal for each region.

21. The system as claimed in claim 14 , wherein the video signal quality measure determiner is further configured to determine the level of clipping for the set of pixels of the original and the processed video signals by determining a portion of the respective sets of pixels having the luminance value that falls outside the clipping value range.