Pixel image enhancement system and method

• US 6,038,348 A
• Filed: 07/24/1996
• Issued: 03/14/2000
• Est. Priority Date: 07/24/1996
• Status: Expired due to Term

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Oak Technology Partners (Qualcomm, Inc.)
• Inventors: Carley, Adam
• Primary Examiner(s): Lee, Thomas D.
• Application Number:
  US08/685,804
• Time in Patent Office: 1,329 Days
• Field of Search: 382/254, 382/268, 382/162, 382/266, 358/447, 358/448, 358/455, 358/462, 358/534
• US Class Current: 382/268
• CPC Class Codes: H04N 1/40068 Modification of image resolution, i.e. determining the values of picture elements at new relative positions H04N1/3935 takes precedence
• CPC Class Codes: H04N 1/4092 Edge or detail enhancement

Abstract

A pixel image enhancement system which operates on color or monochrome source images to produce output cells the same size as the source pixels but not spatially coincident or one-to-one correspondent with them. By operating upon a set of input pixels surrounding each output cell with a set of logic operations implementing unique Boolean equations, the system generates "case numbers" characterizing inferred-edge pieces within each output cell. A rendering subsystem, responsive to the case numbers and source-pixel colors, then produces signals for driving an output device (printer or display) to display the output cells, including the inferred-edge pieces, to the best of the output device'"'"'s ability and at its resolution.

Claims

1. A computational method for converting a digitized source color image, containing at least three different colors contiguously disposed, into a second electronic color image of different effective spatial resolution, comprising:

forming a scanned sequence of examination windows into said digitized color image, said examination windows being at least three pixels high and at least three pixels wide;

defining a corresponding scanned sequence of elemental inferral areas smaller than, and substantially centered within, said examination windows;

computing, in response to the pixels within the examination windows, at least one inferred-edge piece within at least some of said elemental inferral areas by separately computing unoriented inferred-edge pieces and separately computing an orientation to be applied to said unoriented inferred-edge prices; and

combining the said inferred-edge pieces within at least one said elemental inferral-area, with color data from the source color image, to produce one elemental unit of said second electronic color image.

2. The method of claim 1 where said second electronic color image comprises a standard array of binary coded pixels.

3. The method of claim 1 where said second electronic color image is formatted for displaying on a color printer.

4. The method of claim 1 where said second electronic color image is formatted for display on a color display device.

5. The method of claim 4 where said color display device comprises a cathode ray tube.

6. The method of claim 4 where said color display device is a multiresolution display operated in a higher resolution mode than the resolution of the said digitized color image.

7. The method of claim 1 where combining inferred-edge pieces includes storage means for storing one previous scan line of computed elemental-inferral.

8. The method of claim 1 where said different effective spatial resolution is a decreased resolution.

9. The method of claim 1 where said different effective spatial resolution is an increased resolution.

10. The method of claim 1 where said examination window is rectangular and has an even number of pixels in one dimension and an odd number of pixels in the other dimension.

11. The method of claim 1 where said examination window is rectangular and has an even number of pixels in both dimensions.

12. The method of claim 1 where said examination window has variable size.

13. The method of claim 1 where said examination window is elliptical.

14. The method of claim 1 where said elemental inferral area is equal in area and aspect ratio to the input pixels in said digitized color image.

15. The method of claim 1 where said elemental inferral area at least partially overlaps two adjacent input pixels in said digitized color image.

16. The method of claim 1 where said elemental inferral area at least partially overlaps four touching input pixels in said digitized color image.

17. The method of claim 1 where said step of computing said inferred-edge pieces computes either zero, one, or two said inferred-edge pieces within a given said elemental inferral area.

18. The method of claim 1 where the step of computing comprises selecting from among a predefined set of no more than 1000 predefined inferred-edge pieces.

19. The method of claim 18 where said selection is represented as a binary case number.

20. The method of claim 18 where said selection is represented as an active signal on one among a set of conductors, said set of conductors corresponding to said set of predefined inferred-edge pieces.

21. The method of claim 1 where four possible orientations constitute all possible combinations of vertical and horizontal mirror imaging of unoriented edge pieces.

22. The method of claim 1 where eight possible orientations constitute all possible combinations of vertical and horizontal mirror imaging and 90 degree rotation of the unoriented inferred-edge pieces.

23. The method of claim 1 further including computing an intermediary map of existing edges in said digitized color image and within said examination window.

24. The method of claim 23 where said intermediary map of existing edges designates an edge as present between two contiguous source pixels when said contiguous source pixels differ at all in color.

25. The method of claim 24 where said two contiguous source pixels includes pair of pixels diagonally disposed with respect to each other and touching only at a shared corner.

26. The method of claim 23 where said intermediary map of existing edges designates an edge as present between two contiguous source pixels when said contiguous source pixels differ in color by more than a given threshold.

27. The method of claim 26 where said difference in color between contiguous pixels is computed as approximately representative of their psychological color difference.

28. The method of claim 26 where said given threshold is dynamically optimized.

29. The method of claim 23 where at least one scan line of said intermediary map of existing edges is buffered in lieu of buffering at least one scan line of said digitized color image.

30. The method of claim 1 where computing inferred-edge pieces includes detecting near-45 degrees edges in said digitized color image.

31. The method of claim 1 where computing inferred-edge pieces includes detecting single-pixel-width features in said digitized color image.

32. The method of claim 31 where detection of single-pixel-width features includes preserving said feature-width in the inferred image.

33. The method of claim 1 where said computation of an inferred edge requires that the source pixels along at least one side of that edge all have substantially the same color.

34. The method of claim 1 including estimating which of two diagonally disposed features is continuous through a given node where said continuity is otherwise ambiguous.

35. The method of claim 1 where the computation further includes knowing that the detection criteria for a given unoriented inferred-edge piece are internally symmetric and means for suppressing the generation of any orientation which is rendered redundant by said symmetry.

36. The method of claim 1 where said computation of said inferred-edge pieces includes detecting of curved edges which are tangent to orientation axes.

37. The method of claim 1 where said computation of inferred-edge pieces computes inferred-edge pieces which approximately join end-to-end with the inferred-edge pieces in adjacent elemental inferral areas.

38. The method of claim 1 where said computation of said inferred-edge pieces includes detecting double-size jags characteristic of sharply curved edges tangent to a 45 degree line.

39. The method of claim 1 where said computation of said inferred-edge pieces favors the longer inferred edge in otherwise ambiguous situations.

40. The method of claim 1 where a said inferred-edge piece comprises at least one straight-line segment represented as a vector.

41. The method of claim 40 whereas said vector or bitmap representation of said inferred-edge pieces is computed by accessing a lookup table.

42. The method of claim 1 where a said inferred-edge pieces are represented as an uncolored, bivalued bitmap of greater resolution than the digitized source color image.

43. The method of claim 42 where said bitmap is generated in run-length encoded form.

44. The method of claim 42 where said vector or bit map representation of said inferral-edge pieces is computed by accessing a lookup table.

45. The method of claim 1 where said elemental unit of said second electronic color image is a pulse of modulated width and position.

46. The method of claim 45 where said pulse is also modulated in amplitude.

47. The method of claim 1 where said elemental unit of said second electronic color image is a standard red-green-blue binary-encoded pixel.

48. The method of claim 47 further including utilizing the predefined separate locations of the individual primary color subpixels in a fixed-pixel color display for increasing effective luminance resolution.

49. The method of claim 1 where said elemental unit of said second electronic color image is a standard cyan-magenta-yellow-black binary-encoded pixel.

50. The method of claim 1 where said color display device comprises a fixed-pixel flat-panel display.

51. A computational method for converting a digitized source color image, containing at least three different colors contiguously disposed, into a second electronic color image of different effective spatial resolution, comprising:

forming a scanned sequence of examination windows into said digitized color image, said examination windows being at least three pixels high and at least three pixels wide;

defining a corresponding scanned sequence of elemental inferral areas smaller than, and substantially centered within, said examination windows;

computing, in response to the pixels within the examination windows, at least one inferred-edge piece within at least some of said elemental inferral areas, said computing comprising selecting from among a predefined set of inferred-edge pieces, said selecting comprising detecting major subfeatures shared by a plurality of candidate inferred-edge pieces within the set of inferred-edge pieces; and

combining the said inferred-edge pieces within at least one said elemental inferral-area, with color data from the source color image, to produce one elemental unit of said second electronic color image.

52. The method of claim 51 where exactly two said subfeature detections are combined to select the desired inferred-edge piece.

53. The method of claim 51 where said detection of a major subfeature serves to inhibit selection of a particular inferred-edge piece.

54. The method of claim 53 where said inhibitory subfeature is a local checkerboard pattern of pixels in said examination window.

55. The method of claim 53 where said subfeature is a single-pixel-sized typographic serif.

56. The method of claim 53 where said subfeature is a single pixel-sized typographic cross-stroke.

57. The method of claim 51 where selecting said inferred-edge piece includes prioritizing among multiple inferred-edge piece candidates of a given orientation which would be otherwise selected.

58. A computational method for converting a digitized source color image, containing at least three different colors contiguously disposed, into a second electronic color image of different effective spatial resolution, comprising:

forming a scanned sequence of examination windows into said digitized color image, said examination windows being at least three pixels high and at least three pixels wide;

defining a corresponding scanned sequence of elemental inferral areas smaller than, and substantially centered within, said examination windows;

computing, in response to the pixels within the examination windows, at least one inferred-edge piece within at least some of said elemental inferral areas; and

combining the said inferred-edge pieces within at least one said elemental inferral-area, with color data from the source color image, to produce one elemental unit of said second electronic color image; and

repeating the foregoing steps to form the second electonic image, where the resolution of the source color image is the same as the nominal resolution of an output device and the said elemental units of said second electronic color image are positioned on scan lines halfway between the scan lines of said computed elemental inferral-areas.