Black white image compression having print density control

• US 20050169539A1
• Filed: 02/03/2004
• Published: 08/04/2005
• Est. Priority Date: 02/03/2004
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Prakash, Ravinder
• Granted Patent: US 7,515,758 B2
• Time in Patent Office: Days
• US Class Current: 382/232
• CPC Class Codes: G06T 3/4023 based on decimating pixels or lines of pixels; based on inserting pixels or lines of pixels
• CPC Class Codes: H04N 1/40068 Modification of image resolution, i.e. determining the values of picture elements at new relative positions H04N1/3935 takes precedence

Abstract

A scaling system and method for compressing a bitonal image that has print density control. A system is disclosed that comprises: a pixel reduction system that generates a scaled image by reducing pixel pairs down to single scaled pixel based on a set of scaling rules; and a line density control system that allows the scaled image to be made lighter, normal or darker by changing the scaling rules.

Claims

1. A scaling system for scaling a bitonal image, comprising:

a pixel reduction system that generates a scaled image by reducing pixel pairs down to single scaled pixel based on a set of scaling rules; and

a line density control system that allows the scaled image to be set to lighter, normal or darker by changing the scaling rules.

2. The scaling system of claim 1, wherein the scaling rules are incorporated into a look-up table.

3. The scaling system of claim 1, wherein the scaling rules map an input comprised of four pixel values to an output comprised of one pixel value, wherein the four pixel values include two values of a pixel pair and two values of two pixels that flank the pixel pair.

4. The scaling system of claim 3, wherein the scaling rules provide for sixteen possible values for the input ranging from binary 0000 to 1111, and two possible values for the output comprising 0 and 1.

5. The scaling system of claim 4, wherein the input values 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110 and 1111 map to outputs 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, respectively for a normal setting.

6. The scaling system of claim 5, wherein the line density control system sets the outputs associated with inputs 0011 and 0101 to 0 to achieve a darker image.

7. The scaling system of claim 5, wherein the line density control system sets the outputs associated with inputs 1010 and 1100 to 1 to achieve a lighter image.

8. The scaling system of claim 1, wherein the bitonal image comprises a black white image.

9. The scaling system of claim 4, wherein the scaling rules are optimized to preserve transition and isolated attributes, and substantially maintain relative geographic position of image attributes.

10. The scaling system of claim 1, further comprising an automated density selection system that automatically determines whether the scaled image should be made lighter, normal or darker.

11. The scaling system of claim 10, wherein the automated density selection system analyzes data selected from the group consisting of:

stroke width, font size, and print density.

12. A program product stored on a recordable medium for scaling a bitonal image, comprising:

means for generating a scaled image by reducing pixel pairs down to single scaled pixel based on a set of scaling rules; and

means for changing the scaling rules to make the scaled image lighter, normal or darker.

13. The program product of claim 12, wherein the scaling rules are incorporated into a look-up table.

14. The program product of claim 12, wherein the scaling rules map an input comprised of four pixel values to an output comprised of one pixel value, wherein the four pixel values include two values of a pixel pair and two values of two pixels that flank the pixel pair.

15. The program product of claim 14, wherein the scaling rules for a normal setting provide for sixteen possible values for the input ranging from binary 0000 to 1111, and two possible values for the output of 0 and 1, and wherein the input values 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110 and 1111 map to outputs 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, respectively.

16. The program product of claim 15, wherein said means for changing the scaling rules sets the outputs associated with inputs 0011 and 0101 to 0 to achieve a darker image.

17. The program product of claim 15, wherein said means for changing the scaling rules sets the outputs associated with inputs 1010 and 1100 to 1 to achieve a lighter image.

18. The program product of claim 12, wherein the bitonal image comprises a black white image.

19. The program product of claim 12, further comprising means for automatically determining whether the scaled image should be made lighter, normal or darker.

20. The program product of claim 19, wherein the determining means analyzes data selected from the group consisting of:

stroke width, font size and print density.

21. A method for scaling a bitonal image, comprising:

selecting a line density setting;

determining a set of scaling rules based on the selected line density setting; and

generating a scaled image by reducing pixel pairs down to single scaled pixels based on a set of scaling rules.

22. The method of claim 21, wherein the step of selecting a line density setting is done automatically by analyzing data on the bitonal image, wherein the data is selected from the group consisting of:

stroke width, font size, and print density.

23. The method of claim 21, wherein the line density setting is selected from the group consisting of:

light, normal and dark.

24. The method of claim 23, wherein scaling rules map an input comprised of four pixel values to an output comprised of one pixel value, wherein the four pixel values include two values of a pixel pair and two values of two pixels that flank the pixel pair.

25. The method of claim 24, wherein the scaling rules for a normal setting provide for sixteen possible values for the input ranging from binary 0000 to 1111, and two possible values for the output of 0 and 1, and wherein the input values 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110 and 1111 map to outputs 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, respectively.

26. The method of claim 25, wherein the scaling rules set the outputs associated with inputs 0011 and 0101 to 0 to achieve a darker image.

27. The method of claim 25, wherein the scaling rules set the outputs associated with inputs 1010 and 1100 to 1 to achieve a lighter image.