Apparatus and methods for de-screening scanned documents
View Patent ↗Apparatus and methods for de-screening an image signal utilizing a bank of filters to provide several increasingly blurred versions of the original image signal is disclosed. At any given time, one or more of the blurred versions are created, on a pixel-by-pixel basis. The outputs from a selected pair of blurred signals are then blended together to create a variable blending output that can vary smoothly from no blurring to maximum blurring in a smooth and continuous manner. In addition, the apparatus and methods provide enhanced text and line art by using a variable un-sharp masking mechanism with independent post-blur sharpening control, and detect and enhance neutral (no-color) output pixels.
1. A method for de-screening image data, comprising:
generating an estimated screen frequency of the image data;
selecting two or more filters from a filter bank based directly on the estimated screen frequency and one or more limit parameters;
filtering the image data using the selected two or more filters from the filter bank such that the image data is filtered by each of the selected two or more filters resulting in two or more filtered image data each corresponding to either the entire image data or a same portion of the image data; and
blending the two or more filtered image data to form blended image data.
2. The method of claim 1 , further comprising
generating a blend select signal that indicates how the two or more filtered image data are to be blended.
3. The method of claim 2 , further comprising:
sharpening selected portions of blended image data based on luminance of the blended image data.
4. The method of claim 3 , the sharpening comprising:
increasing sharpness of a selected portion if a luminance of the selected portion is below a predetermined threshold, a magnitude of sharpness being increased with increasing magnitude of the luminance.
5. The method of claim 1 , further comprising:
generating intermediate filter selecting signals based on the estimated screen frequency;
generating a filter selecting signal based on the intermediate filter selecting signals and the one or more limit parameters;
selecting the two or more filters from the filter bank based on the filter selecting signal.
6. The method of claim 2 , further comprising:
selecting a luminance component of a portion of the blended image data; and
adjusting the luminance component of the portion of the blended image data based on a sharpness control signal.
7. The method of claim 2 , further comprising:
selecting chroma components of a portion of the blended image data; and
adjusting the chroma components of the portion of the blended image data based on a neutral control signal.
8. The method of claim 2 , wherein the operations of generating, selecting filtering and blending are performed dynamically.
9. An apparatus to de-screen image data, comprising:
a screen frequency estimater to generate an estimated screen frequency of the image data;
a filter selector to select two or more filters from a filter bank based directly on the estimated screen frequency and one or more limit parameters;
a filterer to filter the image data using the selected two or more filters from the filter bank such that the image data is filtered by each of the two or more filters to result in two or more filtered image data each corresponding to either the entire image data or a same portion of the image data; and
a filter output blender to blend the two or more filtered image data into blended image data.
10. The apparatus of claim 9 , further comprising:
a blend selector to generate a blend select signal that indicates how the outputs of the selected two or more filters are to be blended.
11. The apparatus of claim 10 , further comprising:
an image data sharpener to sharpen selected portions of blended image data based on luminance of the selected portions.
12. The apparatus of claim 11 , wherein the image data sharpener increases sharpness of a selected portion if a luminance of the selected portion is below a predetermined threshold, a magnitude of sharpness being increased with increasing magnitude of the luminance.
13. The apparatus of claim 9 , wherein the filter selector generates intermediate filter selecting signals based on the estimated screen frequency, and generates the filter selecting signal based on the intermediate filter selecting signals and one or more limit parameters.
14. The apparatus of claim 10 , further comprising:
an image data neutralizer to neutralize selected portions of blended image data based on chroma components of the selected portions.
15. A xerographic marking device incorporating the apparatus of claim 9 .
16. A scanning device incorporating the apparatus of claim 9 .
17. A digital photocopier incorporating the apparatus of claim 9 .
18. An apparatus to de-screen image data comprising:
means for generating an estimated screen frequency of the image data;
means for selecting two or more filters from a filter bank based directly on the estimated screen frequency and one or more limit parameters;
means for filtering the image data using the selected two or more filters from the filter bank such that the image data is filtered by each of the two or more filters resulting in two or more filtered image data each corresponding to either the entire image data or a same portion of the image data; and
means for blending the two or more filtered image data into blended image data.
19. The apparatus of claim 18 , further comprising:
means for increasing sharpness of a selected portions of blended image data if a luminance of a selected portion is below a predetermined threshold, a magnitude of sharpness being increased with increasing magnitude of the luminance.