Colour detection

1. A method of detecting representative colour content in an image, the method comprising:

establishing a set of colour difference values of pixels derived from the said image;

deriving a skew parameter of the statistical distribution of said set of values; and

determining the presence of representative colour by analysing the skew parameter.

2. A method according to claim 1 where the skew parameter is derived from an upper percentile, a lower percentile and a median value of the statistical distribution of colour difference values of the said pixels and representative colour is detected when the said skew parameter exceeds a threshold.

3. A method according to claim 1 where results from the analysis of more than one colour difference value from each pixel are analysed.

4. A method according to claim 1 where at least two related images are analysed and analysis results from separate images are used to derive a single detection result.

5. A method according to claim 1 where the set of colour difference values correspond to pixels from a defined region within the image.

6. A method according to claim 1 where the distribution of spatially filtered colour difference values of pixels is analysed.

7. A method according to claim 1 comprising the step of deriving a histogram of the statistical frequency distribution of colour difference values.

8. A method according to claim 7 where the histogram is smoothed prior to analysis.

9. A method according to claim 1 where the detection result depends upon an average luminance level.

10. A method according to claim 8 where a detection result is discarded if an extreme average luminance value is detected.

11. A method according to claim 1 where the detection result is modified if a high proportion of the colour difference values analysed correspond to high colour saturation.

12. A method according to claim 1 where the detection result is modified if a high proportion of widely separated colour difference values occur in the analysed colour difference values.

13. A non-transitory computer readable storage medium storing therein computer-readable instructions for implementing the method of claim 1 .

14. Apparatus for detecting representative colour content in an image, the apparatus comprising:

a statistical distribution analyser for generating a statistical distribution of a set of colour difference values of pixels derived from the said image; and

a skew analyser for analysing the skew of said statistical distribution, deriving a skew parameter of the statistical distribution of said set of values, and providing the skew parameter to be analyzed for determining the presence of representative colour.

15. Apparatus as claimed in claim 14 comprising a threshold comparator for comparing a skew parameter derived from said statistical distribution with a threshold wherein representative colour is detected when the skew parameter exceeds a threshold.

16. Apparatus as claimed in claim 14 comprising a statistical distribution analyser for generating a second statistical distribution of a second colour difference value of pixels derived from the said image; and a skew analyser for analysing the skew of said second statistical distribution.

17. Apparatus according to claim 14 comprising a filter generating a detection result dependent on the analysis results from at least two related images.

18. Apparatus according to claim 14 having a measurement window selector for selecting a defined region within an image to be analysed.

19. Apparatus according to claim 14 , further comprising a filter for spatially filtering colour difference values of pixels.

20. Apparatus according to claim 14 wherein the statistical distribution analyser comprises a statistical frequency analyser for deriving a histogram of the statistical frequency distribution of colour difference values; and a filter for smoothing the histogram prior to analysis.

21. Apparatus according to claim 14 comprising a luminance averager where the detection result depends upon an average luminance level.

22. Apparatus according to claim 14 comprising an extreme luminance value detector where a detection result is discarded if an extreme average luminance value is detected.

23. Apparatus according to claim 14 comprising a colour saturation analyser wherein the detection result is modified if a high proportion of the colour difference values analysed correspond to high colour saturation.

24. Apparatus according to claim 14 comprising colour difference deviation analyser, wherein the detection result is modified if a high proportion of widely separated colour difference values occur in the analysed colour difference values.