Image processing apparatus, image processing method, and computer readable recording medium storing program

Abstract

Disclosed is an image processing apparatus, comprising: an screen processing unit which shifts a position of a screen cell applied to an input image in at least one direction of a main scanning direction and a sub scanning direction of the input image by a first shift amount which changes according to the applied position of the screen cell, when screen processing is performed to the input image by using the screen cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings, and thus are not intended as a definition of the limits of the present invention, and wherein;

FIG. 1 is a diagram showing the constitution of an image processing apparatus according to a present embodiment;

FIG. 2 is a flowchart showing the screen processing executed in the image processing apparatus of FIG 1;

FIG. 3 is a view showing an example of a screen cell;

FIG. 4 is a diagram showing an input-output characteristic defined by threshold values in each cell element of the screen cell of FIG. 3;

FIG. 5A is a view showing an application result of a screen cell to an input image in the case where no shifting of the screen cell is performed, and FIG. 5B is a view showing another application result of the screen cell to the input image in the case where the screen cell is periodically shifted;

FIG. 6 is a view showing a shift result of a screen cell in the case of forming a screen angle;

FIG. 7 is a view showing an example where a screen cell is applied to an input image with shifting the screen cell to the input image periodically;

FIG. 8 is a view showing a screen processing result in the case where no shifting of a screen cell is performed;

FIG. 9 is a view showing a screen processing result in the case of shifting a screen cell periodically;

FIG. 10 is a diagram showing the constitution of an image processing apparatus in the case of performing tone correction according to the shift amount of a screen cell;

FIG. 11 is a view showing an example of a test pattern used to create a LUT used for tone correction; and

FIGS. 12A and 12B are views showing other examples of the screen cell.

Claims

1. An image processing apparatus, comprising: an screen processing unit which shifts a position of a screen cell applied to an input image in at least one direction of a main scanning direction and a sub scanning direction of the input image by a first shift amount which changes according to the applied position of the screen cell, when screen processing is performed to the input image by using the screen cell.

2. The image processing apparatus of claim 1, wherein the screen processing unit periodically changes the first shift amount of the screen cell.

3. The image processing apparatus of claim 2, wherein the screen processing unit shifts the screen cell by a total shift amount acquired by adding a second shift amount defined according to a screen angle to the periodically changing first shift amount, when the screen angle is provided.

4. The image processing apparatus of claim 1, further comprising: a tone correction unit which performs a tone correction to the input image according to a variation of a screen pattern shape caused by the shifting of the screen cell,wherein the screen processing unit performs the screen processing to the. input image which has been subjected to the tone correction.

5. An image processing method, comprising the step of: shifting a position of a screen cell applied to an input image in at least one direction of a main scanning direction and a sub scanning direction of the input image by a first shift amount which changes according to the applied position of the screen cell, when screen processing is performed to the input image by using the screen cell.

6. The image processing apparatus of claim 4, wherein the first shift amount of the screen cell changes periodically.

7. The image processing apparatus of 2, wherein the shifting step is to shift the screen cell by a total shift amount acquired by adding a second shift amount defined according to a screen angle to the periodically changing first shift amount, when the screen angle is provided.

8. The image processing apparatus according to claim 1, further comprising: performing a tone correction to the input image according to a variation of a screen pattern shape caused by the shifting of the screen cell,wherein the screen processing is performed to the input image which has been subjected to the tone correction.

9. A computer readable recording medium storing a program, the program making a computer function as: an screen processing unit which shifts a position of a screen cell applied to an input image in at least one direction of a main scanning direction and a sub scanning direction of the input image by a first shift amount which changes according to the applied position of the screen cell, when screen processing is performed to the input image by using the screen cell.

10. The computer readable recording medium of claim 9, wherein the computer functioning as the screen processing unit periodically changes the first shift amount of the screen cell.

11. The computer readable recording medium of claim 10, wherein the computer functioning as the screen processing unit shifts the screen cell by a total shift amount acquired by adding a second shift amount defined according to a screen angle to the periodically changing first shift amount, when the screen angle is provided.

12. The computer readable recording medium of claim 9, further making the computer function as: a tone correction unit which performs a tone correction to the input image according to a variation of a screen pattern shape caused by the shifting of the screen cell,wherein the computer functioning as the screen processing unit performs the screen processing to the input image which has been subjected to the tone correction.

13. An image processing apparatus, comprising: a screen processing unit which repeatedly applies a screen cell to an input image in two dimension, so as to perform screen processing to the input image,wherein the screen processing unit establishes a state in which relative positions of the repeatedly applied screen cell change periodically in a predetermined direction of the input image.

14. The image processing apparatus of claim 13, further comprising: a tone correction unit which performs a tone correction to the input image according to a variation of a screen pattern shape caused by the shifting of the screen cell,wherein the screen processing unit performs the screen processing to the input image which has been subjected to the tone correction.

15. An image processing apparatus, comprising the steps of: when the screen cell is repeatedly applied to an input image in two dimension so as to perform screen processing to the input image, shifting a screen cell to be a state in which relative positions of the repeatedly applied screen cell change periodically in a predetermined direction of the input image.

16. The image processing apparatus of claim 15, further comprising the step of: performing a tone correction to the input image according to a variation of a screen pattern shape caused by the shifting of the screen cell,wherein the screen processing is performed to the input image which has been subjected to the tone correction.

17. A computer readable recording medium storing a program, the program making a computer function as: a screen processing unit which repeatedly applies a screen cell to an input image in two dimension, so as to perform screen processing to the input image,wherein the screen processing unit establishes a state in which relative positions of the repeatedly applied screen cell change periodically in a predetermined direction of the input image.

18. The computer readable recording medium of claim 17, wherein the program further makes the computer function as: a tone correction unit which performs a tone correction to the input image according to a variation of a screen pattern shape caused by the shifting of the screen cell,wherein the computer functioning as the screen processing unit performs the screen processing to the input image which has been subjected to the tone correction.