Mosquito noise filtering
In one aspect, a method to reduce compression artefacts, includes generating a first set of weights based on pixel value differences, producing a soft binned histogram from values in a neighborhood of pixels, generating an adapted histogram from the soft binned histogram using interpolation, generating occurrence density weights from the adapted histogram, combining the first set of weights and the occurrence density weights, filtering pixel values a bilateral filter using the combined weights, mixing the filtered pixel values and original pixel values, and outputting the mix of filtered pixel values and original pixel values.
1. A method to reduce compression artefacts, comprising:
receiving an image;
selecting a neighborhood of pixels around each central pixel;
computing differences between central pixel value versus respective neighbor pixel value;
generating a first set of weights based on the pixel value differences;
producing a soft binned histogram from values in a neighborhood of pixels;
generating an adapted histogram from the soft binned histogram using interpolation;
generating occurrence density weights from the adapted histogram;
combining the first set of weights and the occurrence density weights;
filtering pixel values by a bilateral filter using the combined weights;
mixing the filtered pixel values and pixel values from the pixel neighborhood; and
outputting the mix of filtered pixel values and pixel values from the pixel neighborhood.
2. The method of claim 1 , further comprising deriving mix control from the adapted histogram and generating a mix control signal specifying a weighted average between filtered and pixel values from the pixel neighborhood to output.
3. The method of claim 1 , wherein the soft binned histogram has 32 or 64 bins.
4. The method of claim 1 , further comprising combining the first set of weights and the occurrence density weights with other weights.
5. The method of claim 4 , wherein the other weights include a lower weight on pixels that are on an edge relative to pixels in flat areas.
6. The method of claim 1 , further comprising detecting a high variance in pixel values and wherein the mixing is based on the detection.
7. The method of claim 6 , wherein the mixing is further based on other mix controls.
8. The method of claim 7 , wherein the other mix controls include an edge detection metric.
9. A method to reduce compression artefacts, comprising:
receiving an image;
selecting a neighborhood of pixels around each central pixel;
computing differences between central pixel value versus respective neighbor pixel value;
producing a soft binned histogram from values in a neighborhood of pixels;
generating an adapted histogram from the soft binned histogram using interpolation;
generating occurrence density weights from the adapted histogram;
generating occurrence density mix control based on the weights;
generating closest central pixel levels based on the occurrence density mix control;
mixing the pixels using the occurrence density mix control and closest central pixel levels; and
outputting the mixed pixels.
10. The method of claim 9 , further comprising generating pixel value difference weights and filtering the pixels before the mixing according to the weights with a bilateral filter.
11. The method of claim 10 , further comprising combining the generated pixel value difference weights with other weights and filtering using the combined weights.
12. The method of claim 11 , wherein the other weights include a lower weight on pixels that are on an edge relative to pixels in flat areas.
13. The method of claim 9 , further comprising detecting a high variance in pixel values and wherein the mixing is based on the detection.
14. The method of claim 13 , wherein the mixing is further based on other mix controls.
15. The method of claim 14 , wherein the other mix controls include an edge detection metric.