Image processing method according to sort of image and image processing apparatus

• US 6,674,546 B1
• Filed: 12/20/1999
• Issued: 01/06/2004
• Est. Priority Date: 12/25/1998
• Status: Expired due to Fees

• Current Assignee: Toshiba Tec Corporation (Toshiba Corporation)
• Original Assignee: Toshiba Tec Corporation (Toshiba Corporation)
• Inventors: Nakahara, Nobuhiko
• Primary Examiner(s): Grant, II, Jerome
• Application Number:
  US09/468,064
• Time in Patent Office: 1,478 Days
• Field of Search: 358/2.1, 358/1.9, 358/3.01, 358/3.06, 358/3.09, 358/3.13
• US Class Current: 358/1.9
• CPC Class Codes: G06K 15/02 using printers

Abstract

The invention provided an image processing method having the steps of, storing a plurality of multi-level dither threshold value arrangements employed for a multi-level dither process, discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, selecting an optimum multi-level dither threshold value arrangement from a plurality of multi-level dither threshold value arrangements on the basis of a discrimination result by the discriminating step, and converting the gradation image data into a second gradation image data expressing one pixel by a second bit number less than the first bit number according to a multi-level dither process on the basis of the selected optimum multi-level dither threshold value arrangement. Accordingly, it is possible to perform a multi-level dither process which establish both of a resolution in a character/line image field and a gradation in a photo image field.

Claims

1. An image processing method comprising the steps of:

storing a plurality of multi-level dither threshold value arrangements employed for a multi-level dither process;

discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation;

selecting an optimum multi-level dither threshold value arrangement from a plurality of multi-level dither threshold value arrangements stored in the storing step on the basis of a discrimination result by the discriminating step; and

converting the gradation image data into a second gradation image data expressing one pixel by a second bit number less than the first bit number according to a multi-level dither process on the basis of the optimum multi-level dither threshold value arrangement selected by the selecting step.

2. An image processing method according to claim 1, wherein the discriminating step includes a discriminating step of discriminating a given first gradation image data expressing one pixel by a first bit number into a character/line image field emphasizing a resolution and a photo image field emphasizing a gradation.

3. An image processing method according to claim 1, wherein the converting step includes a converting step of converting the first gradation image data into a second gradation image data expressing one pixel by a second bit number less than the first bit number according to a multi-level dither process on the basis of the optimum multi-level dither threshold value arrangement selected by the selecting step with using a fixed basic dither matrix regardless of the discrimination result of the discriminating step.

4. An image processing method according to claim 1, wherein the storing step includes a plurality of multi-level dither threshold value arrangements (FIG. 8C and FIGS. 10A to 10D) having a plurality of dither threshold values regularly arranged in a dither matrix setting respective lines to a dither reference threshold value and a dither threshold value plane at arrangements of respectively different angles.

5. An image processing method according to claim 1, wherein the discriminating step includes a discriminating step of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, at a pixel unit.

6. An image processing method according to claim 1, wherein the discriminating step includes a discriminating step of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, at a block unit.

7. An image processing method according to claim 1, wherein the discriminating step includes a discriminating step of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, at an object unit.

8. An image processing method of applying a multi-level dither process to input gradation image data of M bits per one pixel on the basis of a multi-level dither threshold value arrangement so as to convert into image data having smaller gradation number of N bits (M>

N) per one pixel, comprising the steps of;

preparing a plurality of multi-level dither threshold value arrangements regularly arranged at an incline having an angle in an oblique direction so that an order of the multi-level dither threshold value arrangements between a dither reference threshold value and a dither threshold value plane in a dither matrix rides over a plurality of dither threshold value planes, with differentiating incline angles of the arrangement order;

discriminating whether an image field is an image field emphasizing a resolution or an image field emphasizing a gradation with respect to the input gradation image data;

selecting a corresponding multi-level dither threshold value arrangement among the prepared plural number of multi-level dither threshold value arrangements according to an image discrimination result by the discriminating step; and

performing the multi-level dither process on the basis of the selected multi-level dither threshold value arrangement.

9. An image processing method of applying a multi-level dither process to input gradation image data of M bits per one pixel on the basis of a multi-level dither threshold value arrangement so as to convert into image data having smaller gradation number of N bits (M>

N) per one pixel, comprising the steps of;

preparing a plurality of multi-level dither threshold value arrangements regularly arranged at an incline so that an order of the multi-level dither threshold value arrangements between a dither reference threshold value and a dither threshold value plane in a dither matrix increases a spatial frequency in a low density portion of the input gradation image data and regularly arranged at an incline having an angle in an oblique direction so that it rides over a dither threshold value planes between an intermediate density portion and a high density portion, with differentiating angles of the incline of the arrangement order;

discriminating whether an image field is an image field emphasizing a resolution or an image field emphasizing a gradation with respect to the input gradation image data;

selecting a corresponding multi-level dither threshold value arrangement among the prepared plural number of multi-level dither threshold value arrangements according to an image discrimination result by the discriminating step; and

performing the multi-level dither process on the basis of the selected multi-level dither threshold value arrangement.

10. An image processing apparatus comprising:

storing means of storing a plurality of multi-level dither threshold value arrangements employed for a multi-level dither process;

discriminating means of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation;

selecting means of selecting an optimum multi-level dither threshold value arrangement from a plurality of multi-level dither threshold value arrangements stored in the storing step on the basis of a discrimination result by the discriminating step; and

converting means of converting the gradation image data into a second gradation image data expressing one pixel by a second bit number less than the first bit number according to a multi-level dither process on the basis of the optimum multi-level dither threshold value arrangement selected by the selecting step.

11. An image processing apparatus according to claim 10, wherein the discriminating means includes discriminating means of discriminating a given first gradation image data expressing one pixel by a first bit number into a character/line image field emphasizing a resolution and a photo image field emphasizing a gradation.

12. An image processing apparatus according to claim 10, wherein the converting means includes converting means of converting the first gradation image data into a second gradation image data expressing one pixel by a second bit number less than the first bit number according to a multi-level dither process on the basis of the optimum multi-level dither threshold value arrangement selected by the selecting means with using a fixed basic dither matrix regardless of the discrimination result of the discriminating means.

13. An image processing apparatus according to claim 10, wherein the storing means includes a plurality of multi-level dither threshold value arrangements (FIG. 8C and FIGS. 10A to 10D) having a plurality of dither threshold values regularly arranged in a dither matrix setting respective lines to a dither reference threshold value and a dither threshold value plane at arrangements of respectively different angles.

14. An image processing apparatus according to claim 10, wherein the discriminating means includes discriminating means of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, at a pixel unit.

15. An image processing apparatus according to claim 10, wherein the discriminating means includes discriminating means of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, at a block unit.

16. An image processing apparatus according to claim 10, wherein the discriminating means includes discriminating means of discriminating a given first gradation image data expressing one pixel by a first bit number into an image field emphasizing a resolution and an image field emphasizing a gradation, at an object unit.

17. An image processing apparatus of applying a multi-level dither process to input gradation image data of M bits per one pixel on the basis of a multi-level dither threshold value arrangement so as to convert into image data having smaller gradation number of N bits (M>

N) per one pixel, comprising;

preparing means for preparing a plurality of multi-level dither threshold value arrangements regularly arranged at an incline having an angle in an oblique direction so that an order of the multi-level dither threshold value arrangements between a dither reference threshold value and a dither threshold value plane in a dither matrix rides over a plurality of dither threshold value planes, with differentiating angles of the incline of the arrangement order;

discriminating means for discriminating whether an image field is an image field emphasizing a resolution or an image field emphasizing a gradation with respect to the input gradation image data;

selecting means for selecting a corresponding multi-level dither threshold value arrangement among the prepared plural number of multi-level dither threshold value arrangements according to an image discrimination result by the discriminating step; and

multi-level dither process means for performing the multi-level dither process on the basis of the selected multi-level dither threshold value arrangement.

18. An image processing apparatus of applying a multi-level dither process to input gradation image data of M bits per one pixel on the basis of a multi-level dither threshold value arrangement so as to convert into image data having smaller gradation number of N bits (M>

N) per one pixel, comprising;

preparing means for preparing a plurality of multi-level dither threshold value arrangements regularly arranged at an incline so that an order of the multi-level dither threshold value arrangements between a dither reference threshold value and a dither threshold value plane in a dither matrix increases a spatial frequency in a low density portion of the input gradation image data and regularly arranged at an incline having an angle in an oblique direction so that it rides over a dither threshold value planes between an intermediate density portion and a high density portion, with differentiating angles of the incline of the arrangement order;

discriminating means for discriminating whether an image field is an image field emphasizing a resolution or an image field emphasizing a gradation with respect to the input gradation image data;

selecting means for selecting a corresponding multi-level dither threshold value arrangement among the prepared plural number of multi-level dither threshold value arrangements according to an image discrimination result by the discriminating step; and

multi-level dither process means for performing the multi-level dither process on the basis of the selected multi-level dither threshold value arrangement.