Method and apparatus for generating halftone output

• US 5,930,396 A
• Filed: 04/22/1997
• Issued: 07/27/1999
• Est. Priority Date: 04/22/1997
• Status: Expired due to Term

• Current Assignee: Adobe Systems Incorporated (Adobe Inc.)
• Original Assignee: Adobe Systems Incorporated (Adobe Inc.)
• Inventors: Wong, Raymond Wai-Keung, Fiala, Edward Reid
• Primary Examiner(s): ROGERS, SCOTT A
• Application Number:
  US08/841,528
• Time in Patent Office: 826 Days
• Field of Search: 382/237, 382/270, 358/456, 358/457, 358/466, 358/458, 358/298, 395/109
• US Class Current: 382/237
• CPC Class Codes: H04N 1/4051 producing a dispersed dots halftone pattern, the dots having substantially the same size different sizes H04N1/4057

Abstract

A method of generating halftone output on an output device. The method includes retrieving at least one table which associates gray levels with halftone results for a region of an output frame including more than one pixel, determining a reference gray level for a tile of an output frame including more than one pixel, using the at least one table to determine a halftone result for the reference gray level, storing the halftone result for the reference gray level to the tile of the output frame, and delivering the output frame to the output device. The table may be generated from a set of thresholds, which may be a threshold array. A first table may associates gray levels with codes and a second table may associates codes with halftone results, and the method may include converting the reference gray level to a reference code with the first table and converting the reference code to the halftone result for the reference gray level with the second table. Converting the reference gray level to a code may occur during a front-end interpretation and converting the reference code to the halftone result may occur during a back-end rendering.

Claims

1. A method of generating halftone output on an output device, comprising:

retrieving a plurality of tables which associate gray levels with halftone results for a region of an output frame including more than one pixel;

determining a reference gray level from a plurality of pixels of an image for a tile of an output frame including more than one pixel;

determining a position of the tile in the output frame;

selecting one of the tables from the plurality of tables based on the position of the tile;

using the selected table to determine a halftone result for the reference gray level;

storing the halftone result for the reference gray level to the tile of the output frame; and

delivering the output frame to the output device.

2. The method of claim 1 further comprising:

generating the table from a set of thresholds.

3. The method of claim 2 wherein the set of thresholds is a threshold array.

4. The method of claim 1 wherein the tile is rectangular.

5. The method of claim 4 wherein the tile is 2×

2 pixels.

6. The method of claim 4 wherein the tile is 4×

4 pixels.

7. The method of claim 1 further comprising:

compressing the reference gray level.

8. The method of claim 1 further comprising race-halftoning in the output device.

9. A method of generating halftone output on an output device, comprising:

retrieving at least one table which associates gray levels with halftone results for a region of an output frame including more than one pixel;

determining a reference gray level for a tile of an output frame including more than one pixel;

using the at least one table to determine a halftone result for the reference gray level;

storing the halftone result for the reference gray level to the tile of the output frame; and

delivering the output frame to the output device;

wherein the at least one table includes a first table which associates gray levels with codes and a second table which associates codes with halftone results, and wherein using the at least one table includes converting the reference gray level to a reference code with the first table and converting the reference code to the halftone result for the reference gray level with the second table.

10. The method of claim 9 wherein converting the reference gray level to a code occurs during a front-end interpretation and wherein converting the reference code to the halftone result occurs during a back-end rendering.

11. The method of claim 9 wherein the code represents the number of black pixels in the region.

12. The method of claim 9 further comprising:

compressing the code.

13. A method of generating halftone output on an output device, comprising:

dividing an output frame into a plurality of tiles, each tile including more than one pixel;

retrieving a plurality of tables which associate gray levels with halftone results for a region of the output frame, the region including more than one pixel;

for each tile,

determining a reference gray level from a plurality of pixels in an image,

determining a position of the tile in the output frame,

selecting one of the tables from the plurality of tables based on the position of the tile,

using the selected table to determine a halftone result for the reference gray level, and

storing the halftone result for the reference gray level to the tile of the output frame; and

delivering the output frame to the output device.

14. A method of generating halftone output on an output device, comprising:

receiving an image;

dividing an output frame into a plurality of tiles, each tile including more than one pixel;

retrieving a first plurality of tables which associate gray levels with codes;

retrieving a second plurality of tables which associate codes with halftone results for regions including more than one pixel;

for each tile,

selecting one table from the plurality of first tables and one table from the plurality of second tables based on the position of the tile in the output frame,

determining a reference gray level based on the portion of the image corresponding to the position of the tile in the output frame,

using the selected table from the first plurality of tables to convert the reference gray level to a code,

using the selected table from the second plurality of tables to convert the code to a halftone result, and

storing the halftone result to the tile of the output frame; and

delivering the output frame to the output device.

15. A computer program for generating halftone output on an output device, the program tangibly stored on a computer-readable medium and comprising instructions for causing a computer to:

retrieve a plurality of tables which associate gray levels with halftone results for a region of an output frame including more than one pixel;

determine a reference gray level from a plurality of pixels of an image for a tile of an output frame including more than one pixel;

determine a position of the tile in the output frame;

select one of the tables from the plurality of tables based on the position of the tile;

use the selected table to determine a halftone result for the reference gray level;

store the halftone result for the reference gray level to the tile of the output frame; and

deliver the output frame to the output device.