IMAGE PROCESSING APPARATUS AND METHOD THEREOF

• US 20090262372A1
• Filed: 04/14/2009
• Published: 10/22/2009
• Est. Priority Date: 04/18/2008
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Ochiai, Takashi, Moribe, Shoei
• Granted Patent: US 8,351,083 B2
• Time in Patent Office: Days
• US Class Current: 358/1.900
• CPC Class Codes: H04N 1/4053 with threshold modulated relative to input image data or vice versa

Abstract

Image data of a pixel of interest is inputted, diffusion data diffused from errors occurred by decrease of a tonal number of image data is added to the image data of the pixel of interest, the tonal number of the image data of the pixel of interest, to which the diffusion data has been added, is decreased using an error diffusion method or minimized average error method, and an error occurred in the decrease of the tonal number for the pixel of interest is diffused to pixels close to the pixel of interest. Further, the errors occurred by the decrease of the tonal number of the image data in a predetermined image region are integrated as an integrated error, and a threshold value used in the error diffusion method or minimized average error method is set based on the image data of the pixel of interest and the integrated error.

Claims

1. An image processing apparatus comprising:

an input section, configured to input image data of a pixel of interest;

an adder, configured to add diffusion data diffused from errors occurred by decrease of a tonal number of image data to the image data of the pixel of interest;

a converter, configured to decrease the tonal number of the image data of the pixel of interest, to which the diffusion data has been added, using an error diffusion method or minimized average error method; and

a diffuser, configured to diffuse an error occurred in the decrease of the tonal number for the pixel of interest to pixels close to the pixel of interest,

wherein said apparatus further comprising;

a calculator, configured to integrate the errors occurred by the decrease of the tonal number of the image data in a predetermined image region as an integrated error; and

a threshold setting section, configured to set a threshold value used in the error diffusion method or minimized average error method based on the image data of the pixel of interest and the integrated error.

2. The apparatus according to claim 1, wherein said threshold setting section sets the threshold value based on the image data of the pixel of interest, and a product of the integrated error and a predetermined coefficient.

3. The apparatus according to claim 2, wherein said threshold setting section calculates the threshold value by subtracting the product from a sum of a threshold value uniquely defined from the image data of the pixel of interest and a threshold noise uniquely defined from a pixel position of the pixel of interest.

4. The apparatus according to claim 1, further comprising a coefficient setting section configured to set a coefficient indicating a degree that the integrated error influences the setting of the threshold value, based on the image data of the pixel of interest.

5. The apparatus according to claim 4, wherein said threshold setting section sets the threshold value based on the image data of the pixel of interest, and a product of the integrated error and the coefficient.

6. The apparatus according to claim 5, wherein said threshold setting section calculates the threshold value by subtracting the product from a sum of a threshold value uniquely defined from the image data of the pixel of interest and a threshold noise uniquely defined from a pixel position of the pixel of interest.

7. The apparatus according to claim 4, wherein said coefficient setting section sets a large value as the coefficient in a region of an input image that includes an edge, and sets a small value as the coefficient in a region of the input image that does not include the edge.

8. The apparatus according to claim 1, wherein said calculator restricts the integrated error to an upper limit value when the integrated error exceeds the upper limit value, and restricts the integrated error to a lower limit value when the integrated error is lower than the lower limit value.

9. The apparatus according to claim 1, wherein said threshold setting section sets the threshold value so that the integrated error is drawn to a zero near.

10. An image processing method comprising the steps of:

inputting image data of a pixel of interest;

adding diffusion data diffused from errors occurred by decrease of a tonal number of image data to the image data of the pixel of interest;

decreasing the tonal number of the image data of the pixel of interest, to which the diffusion data has been added, using an error diffusion method or minimized average error method; and

diffusing an error occurred in the decrease of the tonal number for the pixel of interest to pixels close to the pixel of interest,

wherein said method further comprising the steps of;

integrating the errors occurred by the decrease of the tonal number of the image data in a predetermined image region as an integrated error; and

setting a threshold value used in the error diffusion method or minimized average error method based on the image data of the pixel of interest and the integrated error.

11. A computer-readable storage medium storing a computer-executable program for causing a computer to perform an image processing method comprising the steps of:

inputting image data of a pixel of interest;

adding diffusion data diffused from errors occurred by decrease of a tonal number of image data to the image data of the pixel of interest;

decreasing the tonal number of the image data of the pixel of interest, to which the diffusion data has been added, using an error diffusion method or minimized average error method; and

diffusing an error occurred in the decrease of the tonal number for the pixel of interest to pixels close to the pixel of interest,

wherein said method further comprising the steps of;

integrating the errors occurred by the decrease of the tonal number of the image data in a predetermined image region as an integrated error; and

setting a threshold value used in the error diffusion method or minimized average error method based on the image data of the pixel of interest and the integrated error.