METHOD AND APPARATUS FOR SIMULATING 2 BIT-PER-PEL PRINTING ON A BI-LEVEL PRINTER USING INTELLIGENT DOUBLE DOTTING

• US 20040141189A1
• Filed: 01/21/2003
• Published: 07/22/2004
• Est. Priority Date: 01/21/2003
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: International Business Machines Corporation
• Inventors: ERNST, LARRY M., DITTRICH, DANIELLE K.
• Granted Patent: US 7,345,790 B2
• Time in Patent Office: Days
• US Class Current: 358/1.2
• 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 1/405 Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels

Abstract

An image processing method and apparatus for enhancing the quality of a printed image without degrading overall printer performance or throughput by simulating 2 bit pel printing on a bi-level printer using intelligent double dotting. The present invention allows a bi-level printer to print an 2N dpi 1 bit-per-pel image through intelligent double dotting, thus enhancing the half resolution rendered image to approach the print quality as if the image were rendered at full resolution. In one embodiment, an enhanced resolution mode which uses a bi-level printer'"'"'s 1200 dpi mode to print 600 dpi, 2 bit-per-pel images, results in an image having higher resolution quality than rendering the image using traditional halftone methods at either 600 dpi or 1200 dpi. Image enhancement through higher order resolution multiplication is also disclosed.

Claims

1. A method for simulating 2 bit pel printing on a bi-level printer, comprising:

converting an image to an N dpi 8 bit-per-pel image;

halftoning the N dpi 8 bit-per-pel image to an N dpi 2 bit-per-pel image;

converting N dpi 2 bit pels from the N dpi 2 bit-per-pel image to Y2 YN dpi 1-bit pels.

2. The method according to claim 1 wherein the converting N dpi 2 bit pels from the N dpi 2 bit-per-pel image to YN dpi 1-bit pels comprises determining a number of YN 1 bit pels out of the Y2 YN dpi 1-bit pels to turn on based upon a 2 bit pel value of the N dpi 2 bit pels.

3. The method of claim 2 wherein a position of the number of YN dpi 1 bit pels out of the Y2 YN dpi 1-bit pels turned on is determined by scanning a 3×

3 mask over the N dpi 2 bit-per-pel image and using neighborhood information to select the position of the number of YN dpi 1-bit pels representing a center N dpi 2 bit pel.

4. The method of claim 3 wherein the using neighborhood information to select the position of the number of YN dpi 1-bit pels representing the center N dpi 2 bit pel comprises computing a value for a position comprising top, bottom, right and left justification values.

5. The method of claim 4 wherein the value for a position comprising top, bottom, right and left justification values is computed by adding half a value of a justification value of pels that are diagonal to a justified position to a value of a pel directly adjacent the center N dpi 2 bit pel.

6. The method of claim 5 wherein pels are justified according to a predetermined default justification orientation.

7. A method for simulating 2 bit pel printing on a bi-level printer, comprising:

converting an image to an N dpi 8 bit-per-pel image;

halftoning the N dpi 8 bit-per-pel image to an N dpi 2 bit-per-pel image; and

converting N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1 bit pels.

8. The method according to claim 7 wherein the converting N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels comprises determining a number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels to turn on based upon a 2 bit pel value of the N dpi 2 bit pels.

9. The method of claim 8 wherein a position of the number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels turned on is determined by scanning a 3×

3 mask over the N dpi 2 bit-per-pel image and using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing a center N dpi 2 bit pel.

10. The method of claim 9 wherein the using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing the center N dpi 2 bit pel comprises computing a value for a position comprising top, bottom, right and left justification values.

11. The method of claim 10 wherein the value for a position comprising top, bottom, right and left justification values is computed by adding half a value of a justification value of pels that are diagonal to a justified position to a value of a pel directly adjacent the center N dpi 2 bit pel.

12. The method of claim 11 wherein pels are justified according to a predetermined default justification orientation.

13. An apparatus for enhancing the resolution of an image to be printed using a bi-level printer simulating 2 bit pel printing comprising:

a memory for storing an image; and

an image processor, wherein the image processor converts the image to an N dpi 8 bit-per-pel image, halftones the N dpi 8 bit-per-pel image to an N dpi 2 bit-per-pel image and converts N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels.

14. The apparatus according to claim 13 wherein the image processor converts the N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels and determines a number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels to turn on based upon a 2 bit pel value of the N dpi 2 bit pels.

15. The apparatus of claim 14 wherein a position of the number of 2N 1 bit pels out of the 4 2N dpi 1-bit pels turned on is determined by the image processor by scanning a 3×

3 mask over the N dpi 2 bit-per-pel image and using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing a center N dpi 2 bit pel.

16. The apparatus of claim 15 wherein the image processor uses neighborhood information to select'"'"'the position of the number of 4 2N dpi 1-bit pels representing a center N dpi 2 bit pel and computes a value for a position with top, bottom, right and left justification values.

17. The apparatus of claim 16 wherein the value for the position computed with top, bottom, right and left justification values is computed by the image processor by adding half a justification value of pels that are diagonal to a justified position to a value of a pel directly adjacent the center N dpi 2 bit pel.

18. The apparatus of claim 17 wherein pels are justified according to a predetermined default justification orientation contained in the image processor.

19. An article of manufacture comprising a program storage medium readable by a computer, the medium tangibly embodying one or more programs of instructions executable by the computer to perform a method for simulating 2 bit pel printing on a bi-level printer, the method comprising:

converting an image to an N dpi 8 bit-per-pel image;

halftoning the N dpi 8 bit-per-pel image to an N dpi 2 bit-per-pel image;

converting N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels.

20. The article of manufacture according to claim 19, wherein the converting N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels comprises determining a number of 2N 1 bit pels out of the 4 2N dpi 1-bit pels to turn on based upon a 2 bit pel value of the N dpi 2 bit pels.

21. The article of manufacture of claim 20 wherein a position of the number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels turned on is determined by scanning a 3×

3 mask over the N dpi 2 bit-per-pel image and using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing a center N dpi 2 bit pel.

22. The article of manufacture of claim 21 wherein the using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing the center N dpi 2 bit pel comprises computing a value for the position comprising top, bottom, right and left justification values.

23. The article of manufacture of claim 22 wherein the value for the position comprising top, bottom, right and left justification values is computed by adding half a value of a justification value of pels that are diagonal to a justified position to a value of a pel directly adjacent the center N dpi 2 bit pel.

24. The article of manufacture of claim 23 wherein pels are justified according to a predetermined default justification orientation.

25. A printer system, comprising:

a scanner for scanning an input image;

a memory, coupled to the scanner, the memory storing a scanned image; and

an image processor, coupled to the memory, for processing the scanned image in the memory, wherein the image processor converts the image to an N dpi 8 bit-per-pel image, halftones the N dpi 8 bit-per-pel image to an N dpi 2 bit-per-pel image and converts N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels.

26. The printer system according to claim 25 wherein the image processor converts N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels via determining a number of 2N 1 bit pels out of the 4 2N dpi 1-bit pels to turn on based upon a 2 bit pel value of the N dpi 2 bit pels.

27. The printer system of claim 26 wherein a position of the number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels turned on is determined by scanning a 3×

3 mask over the N dpi 2 bit-per-pel image and using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing a center N dpi 2 bit pel.

28. The printer system of claim 27 wherein the using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing the center N dpi 2 bit pel comprises computing a value for the position comprising top, bottom, right and left justification values.

29. The printer system of claim 28 wherein the value for the position comprising top, bottom, right and left justification values is computed by adding half a value of a justification value of pels that are diagonal to a justified position to a value of a pel directly adjacent the center N dpi 2 bit pel.

31. An image enhancing system, comprising:

means for scanning an input image;

means for storing a scanned image coupled to the means for scanning, and

means for processing a stored image coupled to the means for storing, wherein the means for processing converts the stored image to an N dpi 8 bit-per-pel image, halftones the N dpi 8 bit-per-pel image to an N dpi 2 bit-per-pel image and converts N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels in a 2N 1 bit-per-pel image.

30. The printer system of claim 31 wherein pels are justified according to a predetermined default justification orientation.

32. The image enhancing system according to claim 31 wherein the means for processing converts N dpi 2 bit pels from the N dpi 2 bit-per-pel image to 4 2N dpi 1-bit pels via determining a number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels to turn on based upon a 2 bit pel value of the N dpi 2 bit pels.

33. The image enhancing system of claim 32 wherein a position of the number of 2N dpi 1 bit pels out of the 4 2N dpi 1-bit pels turned on is determined by scanning a 3×

3 mask over the N dpi 2 bit-per-pel image and using neighborhood information to select the position of the number of 4 2N dpi 1-bit pets representing a center N dpi 2 bit pel.

34. The image enhancing system of claim 33 wherein the using neighborhood information to select the position of the number of 4 2N dpi 1-bit pels representing the center N dpi 2 bit pel comprises computing a value for the position comprising top, bottom, right and left justification values.

35. The image enhancing system of claim 34 wherein the value for the position comprising top, bottom, right and left justification values is computed by adding half a value of a justification value of pels that are diagonal to a justified position to a value of a pel directly adjacent the center N dpi 2 bit pel.

36. The image enhancing system of claim 35 wherein pels are justified according to a predetermined default justification orientation.