Method and system for hybrid error diffusion processing of image information using dynamic screens based on brightness/darkness settings

• US 5,805,724 A
• Filed: 09/24/1996
• Issued: 09/08/1998
• Est. Priority Date: 09/24/1996
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Feng, Xiao-fan, Metcalfe, David J., Triplett, Roger L., Newell, John T.
• Primary Examiner(s): ROGERS, SCOTT A
• Application Number:
  US08/719,097
• Time in Patent Office: 714 Days
• Field of Search: 382/237, 382/252, 382/270, 382/176, 382/173, 358/456, 358/457, 358/458, 358/460, 358/462, 358/534, 358/535, 358/536, 395/109
• US Class Current: 382/176
• CPC Class Codes: H04N 1/4053 with threshold modulated relative to input image data or vice versa

Abstract

A printing system for rendering marks on a recording medium receives a multi-level grey scale pixel value representing a pixel having a first resolution. A screening circuit generates a screened multi-level grey scale pixel value equal to (G_L -V_i)+(S_i -Th)*Dmp_vi *Mod_Eff wherein G_L is the maximum grey level value of the pixel, V_i is equal to the multi-level grey scale pixel value of the first resolution, S_i is equal to a screen value corresponding to a position of the pixel, the image classification of the pixel and a brightness/darkness setting, The threshold value, Dmp_vi is a video dependent dampening factor, and Mod_Eff is a modulation multiplication factor. An interpolator converts the screened multi-level grey scale pixel value to a second resolution, the second resolution being higher than the first resolution, and a binarization circuit binarizes the converted multi-level grey scale pixel value so as to output a binary signal and an error value, the error value having a resolution equal to the first resolution. The error value is diffused to multi-level grey scale pixel values corresponding to pixels adjacent to the pixel having the first resolution, and the binary signal is converted into a mark on the recording medium.

Claims

1. A method of reducing a number of levels in a multi-level grey scale pixel value representing a pixel and diffusing an error generated from reducing the number of levels, comprising the steps of:

(a) receiving a multi-level grey scale pixel value representing a pixel having a first resolution;

(b) receiving a brightness/darkness setting value;

(c) generating an effect pointer based on an image type of the received multi-level grey scale pixel and a window of pixels surrounding the multi-level grey scale pixel and the brightness/darkness setting value;

(d) selecting, from a plurality of screens, a screen according to the effect pointer;

(e) generating a screen value from the selected screen dependent upon a position of the received pixel;

(f) generating a screened multi-level grey scale pixel value utilizing the screen value;

(g) reducing the number of levels in the screened multi-level grey scale pixel value;

(h) generating an error value as a result of the reduction process in said step (g); and

(i) diffusing the error value to multi-level grey scale pixel values of adjacent pixels.

2. The method as claimed in claim 1, further comprising the step of:

(j) converting the screened multi-level grey scale pixel value to a second resolution prior to the execution of said step (g), the second resolution being higher than the first resolution;

said step (h) generating an error value having a resolution corresponding to the first resolution.

3. The method as claimed in claim 2, wherein said step (j) comprises the substeps of:

(j1) computing a first multi-level grey scale pixel value; and

(j2) computing a second multi-level grey scale pixel value.

4. The method as claimed in claim 3, wherein said step (j) comprises the substep of:

(j3) computing a plurality of multi-level grey scale subpixel values B_n, the multi-level grey scale subpixel values B_n being equal to P0+n(P1-P0)/N, wherein n is equal to 0 to N-1, P0 is equal to the first multi-level grey scale pixel value, P1 is equal to the second multi-level grey scale pixel value, and N is equal to a high addressability characteristic.

5. The method as claimed in claim 4, wherein said step (h) comprises the substeps of:

(h1) calculating a desired output, the desired output being equal to a sum of the first and second multi-level grey scale pixel values divided by two;

(h2) calculating an actual output, the actual output being equal to the number of subpixels being equal to or greater than a threshold value multiplied by a difference between a black reference value and a white reference value divided by a high addressability characteristic; and

(h3) calculating the error value to be equal to the desired output minus the actual output.

6. The method as claimed in claim 1, further comprising the steps of:

(j) generating a modulation multiplication factor based on the effect pointer, the modulation multiplication factor being based on image classification; and

(k) modifying the screen value by the modulation multiplication factor;

said step (f) generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor modified screen value.

7. The method as claimed in claim 6, wherein the screened multi-level grey scale pixel value is equal to ((S_i +G_L -V_i)/2) * M wherein Si is equal to the screen value, G_L is equal to a maximum grey level value for a pixel, Vi is equal to the received multi-level grey scale pixel value, and M is equal to the modulation multiplication factor.

8. The method as claimed in claim 6, wherein the screened multi-level grey scale pixel value is equal to (G_L -V_i)+(S_i -Th) * M wherein S_i is equal to the screen value, G_L is equal to a maximum grey level value for a pixel V_i is equal to the received multi-level grey scale pixel value, Th is a threshold value, and M is equal to the modulation multiplication factor.

9. The method as claimed in claim 6, further comprising the steps of:

(l) generating a dampening screen weight based on the multi-level grey scale pixel value; and

(m) further modifying the screen value based on the generated dampening screen weight;

said step (f) generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor and dampening screen weight modified screen value.

10. The method as claimed in claim 9, wherein the screened multi-level grey scale pixel value is equal to (S_i +G_L -V_i)/2)*D* M wherein S_i is equal to the screen value, G_L is equal to a maximum grey level value for a pixel, V_i is equal to the received multi-level grey scale pixel value, D is the dampening screen weight, and M is equal to the modulation multiplication factor.

11. The method as claimed in claim 9, wherein the screened multi-level grey scale pixel value is equal to (G_L -V_i)+(S_i -Th) *D* M wherein S_i is equal to the screen value, G_L is equal to a maximum grey level value for a pixel V_i is equal to the received multi-level grey scale pixel value, Th is a threshold value, D is the dampening screen weight, and M is equal to the modulation multiplication factor.

12. The method as claimed in claim 1, wherein the brightness/darkness setting value is generated by a user.

13. The method as claimed in claim 1, wherein the brightness/darkness setting value is generated by a scanline video statistic circuit.

14. The method as claimed in claim 1, wherein the brightness/darkness setting value is generated by an auto-windowing circuit.

15. A system for reducing a number of levels in a multi-level grey scale pixel value representing a pixel and diffusing an error generated from reducing the number of levels, comprising:

means for generating a brightness/darkness setting value;

image segmentation means for generating an effect pointer based on an image type of a multi-level grey scale pixel to be processed and a window of pixels surrounding the multi-level grey scale pixel and the generated brightness/darkness setting value;

screen means for selecting, from a plurality of screens, a screen according to the effect pointer and generating a screen value from the selected screen dependent upon a position of the pixel to be processed;

modifying means for generating a screened multi-level grey scale pixel value utilizing the screen value;

threshold means for reducing the number of levels in the screened multi-level grey scale pixel value; and

error means for generating an error value as a result of the reduction process by said threshold means and diffusing the error value to multi-level grey scale pixel values of adjacent pixels.

16. The system as claimed in claim 15, further comprising:

converting means for converting the screened multi-level grey scale pixel value to a second resolution prior to the reduction process by said threshold means, the second resolution being higher than the first resolution;

said error means generating an error value having a resolution corresponding to the first resolution.

17. The system as claimed in claim 16, wherein said converting means computes a plurality of multi-level grey scale subpixel values B_n, the multi-level grey scale subpixel values B_n being equal to P0+n(P1-P0)/N, wherein n is equal to 0 to N-1, P0 is equal to the first multi-level grey scale pixel value, P1 is equal to the second multi-level grey scale pixel value, and N is equal to a high addressability characteristic.

18. The system as claimed in claim 15, further comprising:

modulation means for generating a modulation multiplication factor based on the effect pointer, the modulation multiplication factor being based on image classification; and

means for modifying the screen value by the modulation multiplication factor;

said modifying means generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor modified screen value.

19. The system as claimed in claim 18, further comprising:

dampening means for generating a dampening screen weight based on the multi-level grey scale pixel value; and

said means for modifying further modifying the screen value based on the generated dampening screen weight;

said modifying means generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor and dampening screen weight modified screen value.

20. The system as claimed in claim 15, wherein said means for generating the brightness/darkness setting value is a user interface.

21. The system as claimed in claim 15, wherein said means for generating the brightness/darkness setting value is a scanline video statistic circuit.

22. The system as claimed in claim 15, wherein said means for generating the brightness/darkness setting value is an auto-windowing circuit.

23. A system for reducing a number of levels in a multi-level grey scale pixel value representing a pixel and diffusing an error generated from reducing the number of levels, comprising:

a brightness/darkness circuit to generate a brightness/darkness setting value;

an image segmentation circuit to generate an effect pointer based on an image type of a multi-level grey scale pixel to be processed and a window of pixels surrounding the multi-level grey scale pixel and the generated brightness/darkness setting value;

a screen circuit, including a look-up table, to select, from a plurality of screens, a screen according to the effect pointer and generating a screen value from the selected screen dependent upon a position of the pixel to be processed;

an adder to generate a screened multi-level grey scale pixel value with the screen value;

a threshold circuit to reduce the number of levels in the screened multi-level grey scale pixel value; and

an error diffusion circuit to generate an error value as a result of the reduction process and diffuse the error value to multi-level grey scale pixel values of adjacent pixels.

24. The system as claimed in claim 23, further comprising:

converting means for converting the screened multi-level grey scale pixel value to a second resolution prior to the reduction process by said threshold means, the second resolution being higher than the first resolution;

said error means generating an error value having a resolution corresponding to the first resolution.

25. The system as claimed in claim 23, further comprising:

modulation means for generating a modulation multiplication factor based on the effect pointer, the modulation multiplication factor being based on image classification; and

modifying means for modifying the screen value by the modulation multiplication factor;

said adder generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor modified screen value.

26. The system as claimed in claim 25, further comprising:

dampening means for generating a dampening screen weight based on the multi-level grey scale pixel value; and

said modifying means further modifying the screen value based on the generated dampening screen weight;

said adder generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor and dampening screen weight modified screen value.

27. The system as claimed in claim 23, wherein said brightness/darkness circuit is a user interface.

28. The system as claimed in claim 23, wherein said brightness/darkness circuit is a scanline video statistic circuit.

29. The system as claimed in claim 23, wherein said brightness/darkness circuit is an auto-windowing circuit.

30. A method of screening a multi-level grey scale pixel value representing a pixel, comprising the steps of:

(a) receiving a multi-level grey scale pixel value representing a pixel;

(b) receiving a brightness/darkness setting value;

(c) generating an effect pointer based on an image type of the received multi-level grey scale pixel and the brightness/darkness setting value;

(d) selecting, from a plurality of screens, a screen according to the effect pointer;

(e) generating a screen value from the selected screen dependent upon a position of the received pixel; and

(f) generating a screened multi-level grey scale pixel value utilizing the screen value.

31. The method as claimed in claim 30, further comprising the steps of:

(g) generating a modulation multiplication factor based on the effect pointer, the modulation multiplication factor being based on image classification; and

(h) modifying the screen value by the modulation multiplication factor;

said step (f) generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor modified screen value.

32. The method as claimed in claim 31, wherein the screened multi-level grey scale pixel value is equal to ((S_i +G_L -V_i)/2) * M wherein Si is equal to the screen value, G_L is equal to a maximum grey level value for a pixel, Vi is equal to the received multi-level grey scale pixel value, and M is equal to the modulation multiplication factor.

33. The method as claimed in claim 31, further comprising the steps of:

(i) generating a dampening screen weight based on the multi-level grey scale pixel value; and

(j) further modifying the screen value based on the generated dampening screen weight;

said step (f) generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor and dampening screen weight modified screen value.

34. The method as claimed in claim 33, wherein the screened multi-level grey scale pixel value is equal to (S_i +G_L -V_i)/2)*D* M wherein S_i is equal to the screen value, G_L is equal to a maximum grey level value for a pixel, V_i is equal to the received multi-level grey scale pixel value, D is the dampening screen weight, and M is equal to the modulation multiplication factor.

35. The method as claimed in claim 30, wherein the brightness/darkness setting value is generated by a user.

36. The method as claimed in claim 30, wherein the brightness/darkness setting value is generated by a scanline video statistic circuit.

37. The method as claimed in claim 30, wherein the brightness/darkness setting value is generated by an auto-windowing circuit.

38. A system for screening a multi-level grey scale pixel value representing a pixel, comprising:

means for generating a brightness/darkness setting value;

image segmentation means for generating an effect pointer based on an image type of a multi-level grey scale pixel to be processed and the generated brightness/darkness setting value;

screen means for selecting, from a plurality of screens, a screen according to the effect pointer, and for generating a screen value from the selected screen dependent upon a position of the pixel to be processed; and

modifying means for generating a screened multi-level grey scale pixel value utilizing the screen value.

39. The system as claimed in claim 38, further comprising:

modulation means for generating a modulation multiplication factor based on the effect pointer, the modulation multiplication factor being based on image classification; and

means for modifying the screen value by the modulation multiplication factor;

said modifying means generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor modified screen value.

40. The system as claimed in claim 39, further comprising:

dampening means for generating a dampening screen weight based on the multi-level grey scale pixel value; and

said means for modifying further modifying the screen value based on the generated dampening screen weight;

said modifying means generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor and dampening screen weight modified screen value.

41. A system for screening a multi-level grey scale pixel value representing a pixel, comprising:

a brightness/darkness circuit to generate a brightness/darkness setting value;

an image segmentation circuit to generate an effect pointer based on an image type of a multi-level grey scale pixel to be processed and the generated brightness/darkness setting value;

a screen circuit, including a look-up table, to select, from a plurality of screens, a screen according to the effect pointer and to generate a screen value from the selected screen dependent upon a position of the pixel to be processed; and

an adder to generate a screened multi-level grey scale pixel value based on the screen value.

42. The system as claimed in claim 41, further comprising:

modulation means for generating a modulation multiplication factor based on the effect pointer, the modulation multiplication factor being based on image classification; and

modifying means for modifying the screen value by the modulation multiplication factor;

said adder generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor modified screen value.

43. The system as claimed in claim 42, further comprising:

dampening means for generating a dampening screen weight based on the multi-level grey scale pixel value; and

said modifying means further modifying the screen value based on the generated dampening screen weight;

said adder generating a screened multi-level grey scale pixel value utilizing the modulation multiplication factor and dampening screen weight modified screen value.