Image processing method, image processing apparatus, image forming apparatus, computer program product and computer memory product

• US 20050286791A1
• Filed: 06/22/2005
• Published: 12/29/2005
• Est. Priority Date: 06/23/2004
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Katohgi, Terumitsu
• Granted Patent: US 7,692,817 B2
• Time in Patent Office: Days
• US Class Current: 382/252
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression

Abstract

Image processing is carried out by transforming image data to image data having spatial frequency components, by judging whether the absolute values of the coefficients of the predetermined frequency components of the transformed image data are equal to or more than a predetermined value, by modifying the coefficients of the AC components of the image data depending on the result of the judgment, by inversely transforming the image data having the modified coefficients to image data having spatial coordinate components, by comparing the gray levels of the inversely transformed image data with predetermined values, and by transforming the gray levels to quantized levels corresponding to the result of the comparison. By carrying out proper image processing corresponding to the characteristics of the image, the number of gray levels of the image can be decreased while the characteristic portions of the original image are maintained properly.

Claims

1. An image processing method for carrying out image processing by transforming image data to image data having spatial frequency components and by modifying the coefficients of said spatial frequency components, comprising steps of:

judging whether absolute values of the coefficients of the predetermined frequency components of the transformed image data are equal to or more than a predetermined value;

modifying the coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment;

adding specific values to the modified coefficients of the alternating current (AC) components of the image data;

inversely transforming the image data, to which said specific values are added, to image data having spatial coordinate components;

comparing gray levels of the inversely transformed image data with predetermined values; and

transforming said gray levels to quantized levels corresponding to the result of the comparison.

2. The image processing method as set forth in claim 1, further comprising a step of modifying said coefficients by calculation in the case where it is judged that said absolute values are equal to or more than said predetermined value, by multiplying the coefficients of the alternating current (AC) components having only the spatial frequency components in the horizontal direction and the coefficients of the alternating current (AC) components having only the spatial frequency components in the vertical direction by a real number larger than 1.

3. The image processing method as set forth in claim 2, further comprising a step of modifying said coefficients by calculation in the case where it is judged that said absolute values are equal to or more than said predetermined value, by multiplying said coefficients by a larger (or smaller) real number as the frequency of the alternating current (AC) component is higher (or lower).

4. An image processing method for carrying out image processing by transforming image data to image data having spatial frequency components and by modifying the coefficients of said spatial frequency components, comprising steps of:

judging whether absolute values of the products obtained by multiplying the coefficients of the predetermined frequency components of the transformed image data by the coefficients of the direct current (DC) components of the same are equal to or more than a predetermined value;

modifying the coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment;

adding specific values to the modified coefficients of the alternating current (AC) components of the image data;

inversely transforming the image data, to which said specific values are added, to image data having spatial coordinate components;

comparing gray levels of the inversely transformed image data with predetermined values; and

transforming said gray levels to quantized levels corresponding to the result of the comparison.

5. The image processing method as set forth in claim 4, further comprising a step of modifying said coefficients by calculation in the case where it is judged that said absolute values are equal to or more than said predetermined value, by multiplying the coefficients of the alternating current (AC) components having only the spatial frequency components in the horizontal direction and the coefficients of the alternating current (AC) components having only the spatial frequency components in the vertical direction by a real number larger than 1.

6. The image processing method as set forth in claim 5, further comprising a step of modifying said coefficients by calculation in the case where it is judged that said absolute values are equal to or more than said predetermined value, by multiplying said coefficients by a larger (or smaller) real number as the frequency of the alternating current (AC) component is higher (or lower).

7. An image processing apparatus which has a frequency transform unit for transforming image data to image data having spatial frequency components, and carries out image processing by modifying the coefficients of said spatial frequency components, comprising:

a judging unit for judging whether absolute values of the coefficients of the predetermined frequency components of the image data transformed by said frequency transform unit are equal to or more than a predetermined value;

a calculation unit for modifying the coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment made by said judging unit;

an adding unit for adding specific values to the coefficients of the alternating current (AC) components of the image data modified by said calculation unit;

an inverse transform unit for inversely transforming the image data, to which said specific values are added by said adding unit, to image data having spatial coordinate components; and

a threshold processing unit for comparing gray levels of the image data inversely transformed by said inverse transform unit with predetermined values and for transforming said gray levels to quantized levels corresponding to the result of the comparison.

8. The image processing apparatus as set forth in claim 7, wherein in the case where said judging unit judges that the absolute values are equal to or more than said predetermined value, said calculation unit multiplies the coefficients of the alternating current (AC) components of said image data by a real number larger than 1 or divides the coefficients of the alternating current (AC) components of said image data by a positive real number smaller than 1.

9. The image processing apparatus as set forth in claim 8, wherein in the case where said judging unit judges that the absolute values are equal to or more than said predetermined value, said calculation unit multiplies the coefficients of the alternating current (AC) components having only the spatial frequency components in the horizontal direction and the coefficients of the alternating current (AC) components having only the spatial frequency components in the vertical direction by a real number larger than 1.

10. The image processing apparatus as set forth in claim 9, wherein said calculation unit multiplies said coefficients by a larger (or smaller) real number as the frequency of the alternating current (AC) component is higher (or lower).

11. The image processing apparatus as set forth in claim 10, wherein in the case where said judging unit judges that the absolute values are less than said predetermined value, said calculation unit multiplies the coefficients of the alternating current (AC) components of said image data by a positive real number smaller than 1 or divides the coefficients of the alternating current (AC) components of said image data by a real number larger than 1.

12. An image processing apparatus which has a frequency transform unit for transforming image data to image data having spatial frequency components, and carries out image processing by modifying the coefficients of said spatial frequency components, comprising:

a judging unit for judging whether absolute values of the products obtained by multiplying the coefficients of the predetermined frequency components of the transformed image data by the coefficients of the direct current (DC) components of the same are equal to or more than a predetermined value;

a calculation unit for modifying the coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment made by said judging unit;

an adding unit for adding specific values to the coefficients of the alternating current (AC) components of the image data modified by said calculation unit;

an inverse transform unit for inversely transforming the image data, to which said specific values are added by said adding unit, to image data having spatial coordinate components; and

a threshold processing unit for comparing gray levels of the image data inversely transformed by said inverse transform unit with predetermined values and for transforming said gray levels to quantized levels corresponding to the result of the comparison.

13. The image processing apparatus as set forth in claim 12, wherein

said judging unit judges whether or not absolute values of coefficients of predetermined frequency components of the image data transformed by said frequency transform unit are equal to or larger than a predetermined value,

said adding unit adds specific values to the coefficients of alternating current (AC) components of the image data transformed by said frequency transform unit, when said judging unit judges that the absolute values of the products are not equal to or larger than the predetermined value and the absolute values of the coefficients are equal to or larger than the predetermined value, and

said calculation unit multiplies the coefficients of alternating current (AC) components of the image data transformed by said frequency transform unit by a positive real number smaller than 1, or divides the coefficients of alternating current (AC) components of the image data by a real number larger than 1, when said judging unit judges that the absolute values of the products are not equal to or larger than the predetermined value and the absolute values of the coefficients are not equal to or larger than the predetermined value.

14. The image processing apparatus as set forth in claim 12, wherein

said frequency transform unit transforms the image data into image data having spatial frequency components within a predetermined frequency range, and

said judging unit judges whether or not absolute values of products obtained by multiplying the coefficients of alternating current (AC) components on a low frequency side by the coefficient of direct current (DC) component are equal to or larger than a predetermined value.

15. The image processing apparatus as set forth in claim 14, wherein

said judging unit judges whether or not absolute values of coefficients of predetermined frequency components of the image data transformed by said frequency transform unit are equal to or larger than a predetermined value,

said adding unit adds specific values to the coefficients of alternating current (AC) components of the image data transformed by said frequency transform unit, when said judging unit judges that the absolute values of the products are not equal to or larger than the predetermined value and the absolute values of the coefficients are equal to or larger than the predetermined value, and

said calculation unit multiplies the coefficients of alternating current (AC) components of the image data transformed by said frequency transform unit by a positive real number smaller than 1, or divides the coefficients of alternating current (AC) components of the image data by a real number larger than 1, when said judging unit judges that the absolute values of the products are not equal to or larger than the predetermined value and the absolute values of the coefficients are not equal to or larger than the predetermined value.

16. The image processing apparatus as set forth in claim 12, wherein in the case where said judging unit judges that the absolute values are equal to or more than said predetermined value, said calculation unit multiplies the coefficients of the alternating current (AC) components of said image data by a real number larger than 1 or divides the coefficients of the alternating current (AC) components of said image data by a positive real number smaller than 1.

17. The image processing apparatus as set forth in claim 16, wherein in the case where said judging unit judges that the absolute values are equal to or more than said predetermined value, said calculation unit multiplies the coefficients of the alternating current (AC) components having only the spatial frequency components in the horizontal direction and the coefficients of the alternating current (AC) components having only the spatial frequency components in the vertical direction by a real number larger than 1.

18. The image processing apparatus as set forth in claim 17, wherein said calculation unit multiplies said coefficients by a larger (or smaller) real number as the frequency of the alternating current (AC) component is higher (or lower).

19. The image processing apparatus as set forth in claim 18, wherein in the case where said judging unit judges that the absolute values are less than said predetermined value, said calculation unit multiplies the coefficients of the alternating current (AC) components of said image data by a positive real number smaller than 1 or divides the coefficients of the alternating current (AC) components of said image data by a real number larger than 1.

20. An image forming apparatus including an image processing apparatus which has a frequency transform unit for transforming image data to image data having spatial frequency components, and carries out image processing by modifying the coefficients of said spatial frequency components,

said image processing apparatus, comprising:

a judging unit for judging whether absolute values of the coefficients of the predetermined frequency components of the image data transformed by said frequency transform unit are equal to or more than a predetermined value;

a calculation unit for modifying the coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment made by said judging unit;

an adding unit for adding specific values to the coefficients of the alternating current (AC) components of the image data modified by said calculation unit;

an inverse transform unit for inversely transforming the image data, to which said specific values are added by said adding unit, to image data having spatial coordinate components; and

a threshold processing unit for comparing gray levels of the image data inversely transformed by said inverse transform unit with predetermined values and for transforming said gray levels to quantized levels corresponding to the result of the comparison;

wherein an image is formed on the basis of the image data image-processed by said image processing apparatus.

21. An image forming apparatus including an image processing apparatus which has a frequency transform unit for transforming image data to image data having spatial frequency components, and carries out image processing by modifying the coefficients of said spatial frequency components,

said image processing apparatus, comprising:

a judging unit for judging whether absolute values of the products obtained by multiplying the coefficients of the predetermined frequency components of the transformed image data by the coefficients of the direct current (DC) components of the same are equal to or more than a predetermined value;

a calculation unit for modifying the coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment made by said judging unit;

an adding unit for adding specific values to the coefficients of the alternating current (AC) components of the image data modified by said calculation unit;

an inverse transform unit for inversely transforming the image data, to which said specific values are added by said adding unit, to image data having spatial coordinate components; and

a threshold processing unit for comparing gray levels of the image data inversely transformed by said inverse transform unit with predetermined values and for transforming said gray levels to quantized levels corresponding to the result of the comparison;

wherein an image is formed on the basis of the image data image-processed by said image processing apparatus.

22. The image forming apparatus as set forth in claim 21, wherein

said frequency transform unit transforms the image data into image data having spatial frequency components within a predetermined frequency range, and

said judging unit judges whether or not absolute values of products obtained by multiplying the coefficients of alternating current (AC) components on a low frequency side by the coefficient of direct current (DC) component are equal to or larger than a predetermined value.

23. A computer program product for controlling a computer to carry out image processing by transforming image data to image data having spatial frequency components and by modifying the coefficients of said spatial frequency components, wherein the computer program product comprises:

a computer readable storage medium having computer readable program code means embodied in said medium, said computer readable program code means comprising computer instruction means for;

judging whether absolute values of the coefficients of predetermined frequency components of the transformed image data are equal to or more than a predetermined value;

modifying coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment;

adding specific values to the modified coefficients of the alternating current (AC) components of the image data;

inversely transforming the image data, to which said specific values are added, to image data having spatial coordinate components;

comparing gray levels of the inversely transformed image data with predetermined values; and

transforming said gray levels to quantized levels corresponding to the result of the comparison.

24. The computer program product as set forth in claim 23, wherein said computer instruction means for modifying the coefficients of the alternating current (AC) components of said image data by calculation includes computer instruction means for carrying out multiplication in the case where it is judged that the absolute values are equal to or more than said predetermined value, by multiplying the coefficients of the alternating current (AC) components having only the spatial frequency components in the horizontal direction and the coefficients of the alternating current (AC) components having only the spatial frequency components in the vertical direction by a real number larger than 1.

25. The computer program product as set forth in claim 24, wherein said computer instruction means for modifying the coefficients of the alternating current (AC) components of said image data by calculation includes computer instruction means for multiplying said coefficients by a larger (or smaller) real number as the frequency of the alternating current (AC) component is higher (or lower).

26. A computer program product for controlling a computer to carry out image processing by transforming image data to image data having spatial frequency components and by modifying the coefficients of said spatial frequency components, wherein the computer program product comprises:

a computer readable storage medium having computer readable program code means embodied in said medium, said computer readable program code means comprising computer instruction means for;

judging whether absolute values of the products obtained by multiplying the coefficients of the predetermined frequency components of the transformed image data by the coefficients of the direct current (DC) components of the same are equal to or more than a predetermined value;

modifying coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment;

adding specific values to the modified coefficients of the alternating current (AC) components of the image data;

inversely transforming the image data, to which said specific values are added, to image data having spatial coordinate components;

comparing gray levels of the inversely transformed image data with predetermined values; and

transforming said gray levels to quantized levels corresponding to the result of the comparison.

27. The computer program product as set forth in claim 26, wherein said computer instruction means for modifying the coefficients of the alternating current (AC) components of said image data by calculation includes computer instruction means for carrying out multiplication in the case where it is judged that the absolute values are equal to or more than said predetermined value, by multiplying the coefficients of the alternating current (AC) components having only the spatial frequency components in the horizontal direction and the coefficients of the alternating current (AC) components having only the spatial frequency components in the vertical direction by a real number larger than 1.

28. The computer program product as set forth in claim 27 wherein said computer instruction means for modifying the coefficients of the alternating current (AC) components of said image data by calculation includes computer instruction means for multiplying said coefficients by a larger (or smaller) real number as the frequency of the alternating current (AC) component is higher (or lower).

29. A computer memory product readable by a computer containing a program for controlling a computer to carry out image processing by transforming image data to image data having spatial frequency components and by modifying the coefficients of said spatial frequency components, the program comprising steps of:

judging whether absolute values of the coefficients of predetermined frequency components of the transformed image data are equal to or more than a predetermined value;

modifying coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment;

adding specific values to the modified coefficients of the alternating current (AC) components of the image data;

inversely transforming the image data, to which said specific values are added, to image data having spatial coordinate components;

comparing gray levels of the inversely transformed image data with predetermined values; and

transforming said gray levels to quantized levels corresponding to the result of the comparison.

30. A computer memory product readable by a computer containing a program for controlling a computer to carry out image processing by transforming image data to image data having spatial frequency components and by modifying the coefficients of said spatial frequency components, the program comprising steps of:

judging whether absolute values of the products obtained by multiplying the coefficients of the predetermined frequency components of the transformed image data by the coefficients of the direct current (DC) components of the same are equal to or more than a predetermined value;

modifying coefficients of alternating current (AC) components of said image data by calculation depending on the result of the judgment;

adding specific values to the modified coefficients of the alternating current (AC) components of the image data;

inversely transforming the image data, to which said specific values are added, to image data having spatial coordinate components;

comparing gray levels of the inversely transformed image data with predetermined values; and

transforming said gray levels to quantized levels corresponding to the result of the comparison.