Decoding a Bayer-mask or like coded image
View Patent ↗A Bayer-mask is decoded by forming a decoded green array, calculating red green and blue-green color difference signals, deriving a first full-resolution grid of each colour difference signal using a first interpolation filter; deriving a second full-resolution grid of each colour difference signal using a second interpolation filter taking a larger number of colour difference signal inputs than the first; generating a cross-colour weighting signal; and forming a mixed colour difference signal from the first and second full-resolution grids in accordance with the cross-colour weighting signal.
1. An apparatus for decoding a Bayer-mask or like coded image comprising a value for one of a set of colours at each pixel of the image to provide a decoded value for each of the set of colours at each pixel of the image, the apparatus comprising:
a selected colour interpolation filter configured to derive from the coded image an array having for a selected colour a value at each pixel of the image, said array forming a first decoded colour value output;
a colour differentiator configured to calculate from the array a colour difference signal at each of the pixels associated with other colours;
a first interpolation filter configured to derive a first full-resolution grid of each colour difference signal;
a second interpolation filter configured to derive a second full-resolution grid of each colour difference signal using a larger number of colour difference signal inputs than said first interpolation filter;
a cross colour measurer configured to generate a cross-colour weighting signal having a value at each pixel formed by a sum and difference of the colour difference signals, and further configured to generate a cross-colour suppression signal based on a variance of the cross-colour weighting signal;
a mixer configured to form a mixed colour difference signal from said first and second full-resolution grids in accordance with said cross-colour suppression signal; and
a signal combiner configured to mix said mixed colour difference signal and said first decoded colour value output to derive at least second and third decoded colour value outputs.
2. The apparatus of claim 1 , wherein the selected colour is green and the other colours are red and blue.
3. The apparatus of claim 1 , wherein the variance is formed along an axis on which the colour difference signals are equal.
4. The apparatus of claim 1 , wherein the variance is formed in a rolling window.
5. The apparatus of claim 1 , further comprising an activity measure configured to calculate an activity value at a pixel; wherein the variance of the cross-colour weighting signal is multiplied by said activity value.
6. The apparatus of claim 5 , wherein the activity value is derived by forming the absolute value of a spatial gradient at each pixel and applying a spatial filter.
7. An imaging system comprising a light sensor array, a Bayer mask and apparatus according to claim 1 .
8. The apparatus of claim 1 , wherein the cross colour measurer is configured to generate the cross-colour weighting signal from the sum and difference of the colour difference signals derived from the first interpolation filter.
9. A method of decoding a Bayer-mask or like coded image comprising a value for one of a set of colours at each pixel of the image to provide a decoded value for each of the set of colours at each pixel of the image, the method comprising:
deriving from the coded image an array having for a selected colour a value at each pixel of the image, said array forming a first decoded colour value output;
calculating from the array a colour difference signal at each of the pixels associated with other colours;
deriving a first full-resolution grid of each colour difference signal using a first interpolation filter;
deriving a second full-resolution grid of each colour difference signal using a second interpolation filter that uses a larger number of colour difference signal inputs than said first interpolation filter;
generating a cross-colour weighting signal having a value at each pixel formed by a sum and difference of the colour difference signals;
forming a mixed colour difference signal from said first and second full-resolution grids in accordance with a cross-colour suppression signal derived from a variance of said cross-colour weighting signal; and
combining said mixed colour difference signal and said first decoded colour value output to derive at least second and third decoded colour value outputs.
10. The method of claim 9 , wherein the selected colour is green and the other colours are red and blue.
11. The method of claim 9 , further comprising forming the variance along an axis on which the colour difference signals are equal.
12. The method of claim 9 , further comprising forming the variance in a rolling window.
13. The method of claim 9 , further comprising multiplying the variance of the cross-colour weighting signal by a local activity measure.
14. The method of claim 13 , further comprising deriving the local activity measure by forming the absolute value of a spatial gradient at each pixel and applying a spatial filter.
15. The method of claim 9 , further comprising generating the cross-colour weighting signal from the sum and difference of the colour difference signals derived using the first interpolation filter.
16. A tangible, non-transitory computer program product configured to cause a programmable apparatus to implement a method of decoding in a processor a Bayer-mask or like coded image comprising a value for one of a set of colours at each pixel of the image to provide a decoded value for each of the set of colours at each pixel of the image, the implemented method comprising:
deriving from the coded image an array having for a selected colour a value at each pixel of the image, said array forming a first decoded colour value output;
calculating from the array a colour difference signal at each of the pixels associated with other colours;
deriving a first full-resolution grid of each colour difference signal using a first interpolation filter;
deriving a second full-resolution grid of each colour difference signal using a second interpolation filter that uses a larger number of colour difference signal inputs than said first interpolation filter;
generating a cross-colour weighting signal having a value at each pixel formed by a sum and difference of the colour difference signals;
forming a mixed colour difference signal from said first and second full-resolution grids in accordance with a cross-colour suppression signal derived from a variance of said cross-colour weighting signal; and
combining said mixed colour difference signal and said first decoded colour value output to derive at least second and third decoded colour value outputs.
17. The computer program product of claim 16 , wherein the implemented method further comprises generating the cross-colour weighting signal from the sum and difference of the colour difference signals derived using the first interpolation filter.