Image processing device, image processing method and image processing program

• US 7,369,710 B2
• Filed: 08/26/2004
• Issued: 05/06/2008
• Est. Priority Date: 08/29/2003
• Status: Expired due to Fees

• Current Assignee: Brother Kogyo Kabushiki Kaisha
• Original Assignee: Brother Kogyo Kabushiki Kaisha
• Inventors: Yoshida, Yasunari
• Primary Examiner(s): Tran; Phuoc
• Application Number:
  US10/925,910
• Publication Number:
  US 20050046903A1
• Time in Patent Office: 1,349 Days
• Field of Search: 382/162, 382/252, 382/270, 358/3.03, 358/3.04, 358/3.05, 358/3.22
• US Class Current: 382/252
• CPC Class Codes: H04N 1/4053 with threshold modulated relative to input image data or vice versa

Abstract

An image processing device performs an error diffusion on multilevel input image data to generate multilevel output image data that has fewer levels than the multilevel input image data. The image processing device includes a plurality of setting devices, each of which sets a threshold value to be used at the error diffusion, a threshold value selecting device that randomly selects one of the plurality of setting devices with respect to each pixel to be processed and allows the selected setting device to set a threshold value with respect to the pixel to be processed when the image processing device performs the error diffusion, and a converting device that converts the pixel to be processed into multilevel output image data with fewer levels than multilevel input image data by the error diffusion, in accordance with the threshold value set by the setting device selected by the threshold value selecting device. The plurality of setting devices includes at least a first setting device and a second setting device that sets a threshold value which is higher than a threshold value set by the first setting device.

Claims

1. An image processing device that performs an error diffusion on multilevel input image data to generate multilevel output image data that has fewer levels than the multilevel input image data, comprising:

a plurality of setting devices, each of which sets a threshold value to be used at the error diffusion, the plurality of setting devices including at least a first setting device and a second setting device that sets a threshold value which is higher than a threshold value set by the first setting device;

a threshold value selecting device that randomly selects one of the plurality of setting devices with respect to each pixel to be processed and allows the selected setting device to set a threshold value with respect to the pixel to be processed when the image processing device performs the error diffusion; and

a converting device that converts the pixel to be processed into multilevel output image data with fewer levels than multilevel input image data by the error diffusion, in accordance with the threshold value set by the setting device selected by the threshold value selecting device.

2. The image processing device according to claim 1, wherein the threshold value selecting device selects the first setting device with greater probability than the second setting device.

3. The image processing device according to claim 2, wherein a ratio of selecting the first setting device to the second setting device is higher than 1:

1 and lower than 63;

1.

4. The image processing device according to claim 1, wherein the second setting device sets a random number value as the threshold value.

5. The image processing device according to claim 4, wherein the random number value which is set as the threshold value by the second setting device is generated in a range of L/4 to 3L/4 when a maximum pixel density of the input image data is L-1.

6. The image processing device according to claim 4, wherein the first setting device sets a random number value in a range which is narrower than a range of the threshold value set by the second setting device, as the threshold value.

7. The image processing device according to claim 6, wherein the first setting device sets a random number value of 16 or smaller, as the threshold value.

8. The image processing device according to claim 1, wherein the first setting device sets a fixed value of 8 or smaller, as the threshold value.

9. The image processing device according to claim 1, further comprising a random number generator that stores a random number table which stores a plurality of values in a predetermined random order, wherein the threshold value selecting device selects one of the setting devices, based on a random number referred to from the random number generator in a predetermined order.

10. The image processing device according to claim 9, wherein the random number generator includes a plurality of random number tables, each of which stores a plurality of values in different order from the other random number tables, and the threshold value selecting device selects the random number table, which is different from the previously-selected random number table, and refers to a random number from the random number generator every time m-line(s) (m=whole number) of pixels is processed.

11. The image processing device according to claim 9, wherein the threshold value selecting device stores a plurality of variables whose values are changed in predetermined order every time the variables are selected, adopts one of the plurality of variables as a value representing a stored position of a random number in the random number table and refers to a random number existing at the stored position indicated by the variable, and wherein the variable is changed to one of the other variables every time m-line(s) of pixels is processed.

12. The image processing device according to claim 9, wherein the threshold value selecting device takes on one of differing values, each of which represents a stored position of each random number stored in the random number table, and refers to a random number existing at the stored position indicated by a variable, from the random number table, by using the variable whose value is changed in predetermined order with respect to each pixel to be processed, and wherein an initial value of the variable is randomly changed every time m-line(s) of pixels is processed.

13. The image processing device according to claim 1, comprising a random number calculator that generates a random number by calculation, wherein the threshold value selecting device selects the setting device, based on the random number generated by the random number calculator.

14. The image processing device according to claim 9, generating output image data of each color by performing the error diffusion on input image data of each color that represents a color image by overlapping each other, wherein the random number generator includes a plurality of random number tables, each of which stores a plurality of values in different order from the other random number tables, and the threshold value selecting device selects the random number table, which is different from the previously-selected random number table, in accordance with the color of the input image data to be processed, and refers to a random number from the random number generator.

15. The image processing device according to claim 14, wherein varieties of the plurality of random number tables are less than varieties of the plurality of colors.

16. The image processing device according to claim 1, generating output image data of each color by performing the error diffusion on input image data of each color that represents a color image by overlapping each other, the threshold value selecting device storing a plurality of variables whose values are changed in predetermined order every time the variables are selected, adopts one of the plurality of variables as a value representing a stored position of a random number in the random number table and refers to a random number existing at the stored position indicated by the variable, and wherein the variable is changed to one of the other variables in accordance with the color of the input image data to be processed.

17. The image processing device according to claim 1, wherein the multilevel output image data is bi-level output image data.

18. An image processing method of performing an error diffusion on multilevel input image data and generating multilevel output image data having fewer levels than the multilevel input image data, the method comprising the steps of:

receiving multilevel image data;

randomly selecting one of a first process, which performs an error diffusion by setting a threshold value of a pixel to be processed in a first setting pattern of a plurality of setting patterns for setting a threshold value to be used at the error diffusion, and a second process, which performs an error diffusion by setting a threshold value in a second setting pattern for setting a threshold value which is higher than the threshold value set in the first setting pattern, of the plurality of setting patterns, when the error diffusion is performed with respect to each pixel to be processed; and

generating multilevel image data having fewer levels than the received multilevel image data, with respect to the pixel, by the selected process.

19. A computer-readable medium embodied with an image processing program configured to operate a computer as:

an image processing device that performs an error diffusion on multilevel input image data to generate multilevel output image data with fewer levels than the multilevel input image data;

a plurality of setting devices, each of which sets a threshold value to be used at the error diffusion, the plurality of setting devices including at least a first setting device and a second setting device that sets a threshold value which is higher than a threshold value set by the first setting device;

a threshold value selecting device that randomly selects one of the plurality of setting devices with respect to each pixel to be processed and allows the selected setting device to set a threshold value with respect to the pixel to be processed when the image processing device performs the error diffusion; and

a converting device that converts the pixel to be processed into multilevel output image data with fewer levels than multilevel input image data by the error diffusion, in accordance with the threshold value set by the setting device selected by the threshold value selecting device.