Systems and methods for color defringing
View Patent ↗A system and method for defringing chromatic aberrations that occur in imaging devices such as scanners. The system comprises shift filters to shift lines in the various color planes together. In addition in each color plane, a spread filter is used to compensate for the unequal point spread functions of each color. Furthermore, the results can be enhanced by filtering in the luminance-chrominance space.
1. A color defringing filter:
a red filter;
a blue filter;
a green filter;
an red-green-blue (RGB) to luminance/chrominance (LC) converter coupled to the red filter, the blue filter and the green filter;
a first chroma filter and a second chroma filter coupled to the RGB to LC converter;
wherein the first chroma filter filters a first chroma component of the image in a scan direction and the second chroma filter filters a second chroma component of the image;
wherein filtering the red component comprises applying a red shift filter in accordance with
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where x r is a red component of an input image and y r is a red component of a filtered image y, and filtering the blue component comprises applying a blue shift filter.
2. The filter of claim 1 wherein the red filter comprises a red shift filter shifting a red pixel component by ⅓ pixel and the blue filter comprises a blue shift filter shifting a blue pixel component by ⅓ pixel.
3. The filter of claim 1 wherein the red filter comprises a red spread filter, the blue filter comprises a blue spread filter and the green filter comprises a green spread filter.
4. The filter of claim 3 wherein the red spread filter comprises a high-pass filter, a low-pass filter, or a unity filter, the green spread filter comprises a high-pass filter, a low-pass filter or a unity filter, the blue spread filter comprises a high-pass filter, a low-pass filter or a unity filter.
5. The filter of claim 1 further comprising a luma filter operable to filter the luma component of an image.
6. The filter of claim 5 wherein the luma filter is a high-pass filter.
7. The filter of claim 1 further comprising a LC to RGB converter coupled to the first chroma filter and the second chroma filter.
8. The filter of claim 1 wherein the first chroma filter is a low-pass filter.
9. The filter of claim 1 wherein the second chroma filter is a low-pass filter.
10. A method of color defringing an image having a red component, a blue component and a green component, said method comprising:
filtering the red component;
filtering the blue component;
filtering the green component; converting the red component, blue component, and green component into a luma component, a first chroma component and a second chroma component;
filtering the first chroma component in a scan direction: and
filtering the second chroma component in the scan direction, wherein filtering the red component comprises applying a red shift filter in accordance with
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where x r is a red component of an input image and y r is a red component of a filtered image y, and filtering the blue component comprises applying a blue shift filter.
11. The method of claim 10 wherein filtering the red component comprises applying a red spread filter, filtering the blue component comprises applying a blue spread filter and filtering the green component comprises applying a green spread filter.
12. The method of claim 10 , further comprising filtering the luma component.
13. The method of claim 12 wherein filtering the luma component comprises high-pass filtering.
14. The method of claim 10 , further comprising converting the luma component, the first chroma component and second chroma component into RGB format.
15. The method of claim 10 wherein filtering the first chroma component comprises low-pass filtering.
16. The method of claim 10 wherein filtering the second chroma component comprises low-pass filtering.
17. A color defringing filter operable to defringe an image having a red component, a blue component, and a green component, said filter comprising:
means for filtering the red component;
means for filtering the blue component;
means for filtering the green component;
means for converting the red component, blue component, and green component into a luma component,
a first chroma component and a second chroma component;
means for filtering the first chroma component; and
means far filtering the second chroma component;
wherein filtering the red component comprises applying a red shift filter in accordance with
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where x r is a red component of an input image and y r is a red component of a filtered image y, and filtering the blue component comprises applying a blue shift filter.
18. The filter of claim 17 further comprising means for filtering the luma component.
19. The filter of claim 17 further comprising means for converting the luma component, the first chroma component and second chroma component into RGB format.
20. A scanner comprising:
a scan head;
electronic logic comprising an external interface, processor, and memory;
wherein the memory comprises instructions which causes the processor to defringe a scanned image having a red component, a blue component and a green component by filtering the red component by shifting a red pixel component in a scan direction by ⅓ pixel;
filtering the blue component by shifting a blue pixel component in the scan direction by ⅓ pixel;
converting the red component, blue component, and green component into a luma component, a first chroma component and a second chroma component;
filtering the first chroma component in the scan direction; and
filtering the second chroma component in the scan direction, wherein filtering the red component comprises applying a red shift filter in accordance with
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where x r is a red component of an input image and y r is a red component of a filtered image y, and filtering the blue component comprises applying a blue shift filter.
21. The scanner of claim 20 , wherein the instructions further cause the processor to defringe the scanned image by filtering the luma component.
22. The filter of claim 20 wherein the instructions further cause the processor to defringe the scanned image converting the luma component, the first chroma component and second chroma component into RGB format.
23. The scanner of claim 20 , wherein the scanner is a flatbed scanner, a handheld scanner, a sheet feed scanner, or a multifunctional peripheral.