Image processing method and apparatus and image forming apparatus for reducing moire fringes in output image

• US 20020196470A1
• Filed: 05/23/2002
• Published: 12/26/2002
• Est. Priority Date: 05/24/2001
• Status: Active Grant

• Current Assignee: Clearwire Communications LLC (Deutsche Telekom AG)
• Original Assignee: Ricoh Company Limited
• Inventors: Kawamoto, Hiroyuki, Ohyama, Maki
• Granted Patent: US 7,327,495 B2
• Time in Patent Office: Days
• US Class Current: 358/3.06
• CPC Class Codes: G06T 3/4023 based on decimating pixels or lines of pixels; based on inserting pixels or lines of pixels
• CPC Class Codes: G06T 3/403 Edge-driven scaling; Edge-based scaling
• 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 spatial filter applies a modulation transfer function correction process so as to increase a number of bits of input image data. A high-resolution converter converts the image data into output image data having a density higher than a sampling density of the input image data. One of the spatial filter and the resolution converter processes the image data after the other of the spatial filter and the resolution converter has processed the image data A possibility of saturation of an output of the spatial filter is decreased, thereby decreasing generation of moiré in a saturation calculation.

Claims

1. An image processing method comprising:

applying a spatial filtering process with an input dynamic range wider than an output dynamic range and also applying a high-resolution conversion process to increase an image density of image data.

2. The image processing method as claimed in claim 1, further comprising:

applying a low-resolution conversion process to decrease the image density after applying to the image data the spatial filtering process and the high-resolution conversion process.

3. The image processing method as claimed in claim 2, wherein the low-resolution conversion process changes the image density to an original image density before the high-resolution conversion process is performed.

4. The image processing method as claimed in claim 1, further comprising:

applying a gamma correction process to the image data after applying the high-resolution conversion process.

5. The image processing method as claimed in claim 1, wherein the spatial filtering process is a filtering process of a modulation transfer function correction which sharpens an image edge.

6. The image processing method as claimed in claim 1, wherein an output dynamic range of the high-resolution conversion process is narrower than an input dynamic range of the high-resolution conversion process.

7. The image processing method as claimed in claim 1, wherein the high-resolution conversion process is performed either in a main scanning direction or a subscanning.

8. The image processing method as claimed in claim 1, wherein the high-resolution conversion process increases the image density an integral multiple equal to or higher than twice.

9. An image processing method comprising:

applying to image data a high-resolution conversion to increase an image density of the image data and a spatial filtering process; and

thereafter, applying a low-resolution conversion to decrease the image density.

10. The image processing method as claimed in claim 9, wherein the low-resolution conversion process changes the image density to an original image density before the high-resolution conversion process is performed.

11. The image processing method as claimed in claim 9, further comprising:

applying a gamma-correction process to the image data after applying the high-resolution conversion process.

12. The image processing method as claimed in claim 9, wherein the spatial filtering process is a filtering process of a modulation transfer function correction which sharpens an image edge.

13. The image processing method as claimed in claim 9, wherein an output dynamic range of the high-resolution conversion process is narrower than an input dynamic range of the high-resolution conversion process.

14. The image processing method as claimed in claim 9, wherein the high-resolution conversion process is performed either in a main scanning direction or a subscanning.

15. The image processing method as claimed in claim 9, wherein the high-resolution conversion process increases the image density by an integral multiple equal to or higher than twice.

17. The image processing apparatus as claimed in claim 16, further comprising a gamma-correction unit which applies a gamma-correction to the image data which has been processed by said high-resolution converter.

18. The image processing apparatus as claimed in claim 17, further comprising a low-resolution converter which decreases the density of the gamma-corrected image data.

20. The image reading apparatus as claimed in claim 19, further comprising a gamma-correction unit which applies a gamma-correction to the image data which has been processed by said high-resolution converter.

21. The image reading apparatus as claimed in claim 19, further comprising a low-resolution converter which decreases the density of the gamma-corrected image data.

16. An image processing apparatus comprising:

a spatial filter which applies a modulation transfer function correction process so as to increase a number of bits of input image data; and

a high-resolution converter which converts the image data into output image data having a density higher than a sampling density of the input image data,

wherein one of the spatial filter and the high-resolution converter processes the image data after the other of the spatial filter and the high-resolution converter has processed the image data.

19. An image reading apparatus comprising:

an image reading unit which reads an image or picture to generate image data; and

an image processing apparatus including;

a spatial filter which applies a modulation transfer function correction process so as to increase a number of bits of the image data supplied from said image reading unit; and

a high-resolution converter which converts the image data into output image data having a density higher than a sampling density of the input image data,

wherein one of the spatial filter and the high-resolution converter processes the image data after the other of the spatial filter and the resolution converter has processed the image data.

22. An image forming apparatus comprising:

an image processing apparatus including;

a spatial filter which applies a modulation transfer function correction process so as to increase a number of bits of the image data supplied from said image reading unit; and

a high-resolution converter which converts the image data into output image data having a density higher than a sampling density of the input image data,

wherein one of the spatial filter and the high-resolution converter processes the image data after the other of the spatial filter and the high-resolution converter has processed the image data; and

a printer which forms an image on a recording sheet based on the image data output from said image processing apparatus.

23. The image forming apparatus as claimed in claim 22, further comprising a gamma-correction unit which applies a gamma-correction to the image data which has been processed by said high-resolution converter.

24. The image forming apparatus as claimed in claim 22, further comprising a low-resolution converter which decreases the density of the gamma-corrected image data.

25. The image forming apparatus as claimed in claim 22, further comprising an image reading unit which reads an image or picture to generate the image data so as to supply the image data to said image processing apparatus.

29. The image forming apparatus as claimed in claim 28, wherein said output processing unit includes a simple binarizing unit which converts the gamma corrected image data into binary data as the output data for printing;

and said printer has n dpi and a binary gradation number so as to form a visible image based on the binary data from said simple binarizing unit.

30. The image forming apparatus as claimed in claim 28, wherein said output processing unit includes a binary error diffusion unit which converts the gamma corrected image data into binary data as the output data for printing by a binarization according to an error diffusion method;

and said printer has n dpi and a binary gradation number so as to form a visible image based on the binary data from said binary error diffusion unit.

26. An image forming apparatus comprising:

a resolution converter which converts image data of p bits, which is obtained by optically reading an original image by a sampling density of m dpi, into high-density image data of n dpi and p bits, where n is greater than m;

a spatial filter changing the high-density image data into large dynamic range image data of n dpi and q bits, where q is greater than p;

a gamma correction unit which adjusts an intensity of the image data after being processed by said spatial filter;

an output processing unit which converts the gamma-corrected image data into output data for printing-; and

a printer which produces a visible image based on the output data of said output processing unit.

27. An image forming apparatus comprising:

a spatial filter which changes image data of p bits, which is obtained by optically reading an original image by a sampling density of m dpi, to large dynamic range image data of m dpi and q bits, where q is greater than p;

a resolution converter which converts the large dynamic range image data of m dpi and q bits into high-resolution image data of n dpi and p bits, where n is greater than m;

a gamma correction unit which adjusts an intensity of the image data after being processed by said resolution converter; and

a printer of n dpi and a multiple number of gradation.

28. An image forming apparatus comprising:

a spatial filter which changes image data of p bits, which is obtained by optically reading an original image by a sampling density of m dpi, to large dynamic range image data of m dpi and q bits, where q is greater than p;

a resolution converter which converts the large dynamic range image data of m dpi and q bits into high-resolution image data of n dpi and p bits, where n is greater than m;

a gamma correction unit which adjusts an intensity of the image data after being processed by said resolution converter;

an output processing unit which converts the gamma-corrected image data into output data for printing; and

a printer which produces a visible image based on the output data of said output processing unit.

31. An image forming apparatus comprising:

a spatial filter which changes image data of p bits, which is obtained by optically reading an original image by a sampling density of m dpi, to large dynamic range image data of m dpi and q bits, where q is greater than p;

a resolution converter which converts the large dynamic range image data of m dpi and q bits into high-resolution image data of n dpi and q bits, where n is greater than m;

a gamma correction unit which adjusts an intensity of the image data after being processed by said resolution converter;

an output processing unit which converts the gamma-corrected image data into output data for printing; and

a printer which produces a visible image based on the output data of said output processing unit.

32. An image forming apparatus comprising:

a first resolution converter which converts image data of p bits, which is obtained by optically reading an original image by a sampling density of m dpi, into high-resolution image data of n dpi and p bits, where n is greater than m;

a spatial filter which applies a modulation transfer function (MTF) correction to the high-resolution image data of n dpi and p bits after the conversion of said first resolution converter;

a gamma correction unit which adjusts an intensity of the image data after being processed by said spatial filter;

a second resolution converter which converts the gamma corrected image data of n dpi and p bits into image data of m dpi and q bits;

an output processing unit which converts the image data of n dpi and p bits after the conversion of said second resolution converter into output data for printing; and

a printer which produces a visible image based on the output data of said output processing unit.

33. The image forming apparatus as claimed in claim 32, wherein said first resolution converter changes the image density from m dpi to n dpi in a main scanning direction and from m dpi to m dpi in a subscanning direction.

34. The image forming apparatus as claimed in claim 32, wherein said first resolution converter changes the image density from m dpi to m dpi in a main scanning direction and from m dpi to n dpi in a subscanning direction.

35. The image forming apparatus as claimed in claim 32, wherein n is an integral multiple of m.

36. The image forming apparatus as claimed in claim 35, wherein m is 600 and n is 1200.

38. The image forming apparatus as claimed in claim 37, wherein said first resolution converter changes the image density from m dpi to n dpi in a main scanning direction and from m dpi to m dpi in a subscanning direction.

39. The image forming apparatus as claimed in claim 37, wherein said first resolution converter changes the image density from m dpi to m dpi in a main scanning direction and from m dpi to n dpi in a subscanning direction.

40. The image forming apparatus as claimed in claim 37, wherein n is an integral multiple of m.

41. The image forming apparatus as claimed in claim 40, wherein m is 600 and n is 1200.

37. An image forming apparatus comprising:

a spatial filter which changes image data of p bits, which is obtained by optically reading an original image by a sampling density of m dpi, to large dynamic range image data of m dpi and q bits, where q is greater than p;

a first resolution converter which converts the large dynamic range image data of m dpi and q bits after being processed be said spatial filter into high-resolution image data of n dpi and p bits, where n is greater than m;

a gamma correction unit which adjusts an intensity of the image data after being processed by said first resolution converter;

a second resolution converter which converts the gamma corrected image data of m dpi and p bits into image data of m dpi and p bits;

an output processing unit which converts the image data of m dpi and p bits after the conversion of said second resolution converter into output data for printing; and

a printer which produces a visible image based on the output data of said output processing unit.