Laser print apparatus that generates pulse width value and justification value based on pixels in a multi-bit image

• US 20040156079A1
• Filed: 02/12/2003
• Published: 08/12/2004
• Est. Priority Date: 02/12/2003
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Technology, Ltd. (Marvell Technology Group Limited)
• Inventors: Keithley, Douglas G., Marshall, John D.
• Granted Patent: US 7,280,246 B2
• Time in Patent Office: Days
• US Class Current: 358/3.21
• CPC Class Codes: B41J 2/47 using the combination of scanning and modulation of light
• CPC Class Codes: H04N 1/4056 the pattern varying in one dimension only, e.g. dash length, pulse width modulation [PWM]

Abstract

A laser print apparatus includes a memory for storing a multi-bit image including a plurality of pixels. Each pixel is represented by an N-bit value, wherein N is greater than one. A modulation code generator analyzes three adjacent pixels. The three adjacent pixels include a left pixel, a center pixel, and a right pixel. The modulation code generator is configured to generate a pulse width value based on the value of the center pixel, and a justification value based on the values of the left pixel and the right pixel. A laser print engine forms an output pixel on media based on the pulse width value and the justification value.

Claims

1. A laser print apparatus comprising:

a memory for storing a multi-bit image including a plurality of pixels, each pixel represented by an N-bit value, wherein N is greater than one;

a modulation code generator for analyzing three adjacent pixels, the three adjacent pixels including a left pixel, a center pixel, and a right pixel, the modulation code generator configured to generate a pulse width value based on the value of the center pixel, and a justification value based on the values of the left pixel and the right pixel; and

a laser print engine for forming an output pixel on media based on the pulse width value and the justification value.

2. The laser print apparatus of claim 1, wherein the laser print engine comprises:

a laser configured to be modulated for the output pixel so as to be turned on and off at times corresponding to the justification value for the pixel, and remain on for a time period corresponding to the pulse width value for the pixel.

3. The laser print apparatus of claim 1, wherein the justification value is a 2-bit value representing one of left justify, right justify, split justify, and center justify.

4. The laser print apparatus of claim 1, wherein N=4.

5. The laser print apparatus of claim 1, wherein the pulse width value is a 6-bit value.

6. The laser print apparatus of claim 1, and further comprising:

a first-in first-out (FIFO) device for outputting the three adjacent pixels to the modulation code generator.

7. The laser print apparatus of claim 1, wherein the modulation code generator comprises:

a pulse width code generator for generating the pulse width value by concatenating at least one most significant bit of the center pixel to the least significant end of the value for the center pixel.

8. The laser print apparatus of claim 1, wherein the modulation code generator comprises:

a pulse width code generator for generating the pulse width value by multiplying the value of the center pixel by an integer.

9. The laser print apparatus of claim 1, wherein the modulation code generator comprises:

a first subtracter for subtracting the value of the right pixel from the value of the left pixel, thereby generating a first difference;

a second subtracter for subtracting the value of the left pixel from the value of the right pixel, thereby generating a second difference; and

an adder for adding the value of the left pixel and the value of the right pixel, thereby generating a sum.

10. The laser print apparatus of claim 9, wherein the modulation code generator further comprises:

at least one comparator for comparing the first difference to a first threshold value, comparing the second difference to a second threshold value, and comparing the sum to a third threshold value; and

a justification code generator for generating the justification value based on results of the comparisons made by the at least one comparator.

11. The laser print apparatus of claim 10, wherein the justification code generator generates a justification value indicating left justify if the first difference is greater than the first threshold, generates a justification value indicating right justify if the second difference is greater than the second threshold, generates a justification value indicating split justify if the sum is greater than the third threshold, and generates a justification value indicating center justify if the none of the first, second, or third thresholds are exceeded.

12. The laser print apparatus of claim 1, wherein the modulation code generator comprises:

a look up table for receiving the values of the left, center, and right pixels as an input address, and outputting a corresponding modulation code, the modulation code including the pulse width value and the justification value.

13. The laser print apparatus of claim 1, wherein the modulation code generator comprises:

a look up table for receiving the value of the center pixel and at least one most significant bit of the values for the left and right pixels as an input address, and outputting a corresponding modulation code, the modulation code including the pulse width value and the justification value.

14. The laser print apparatus of claim 1, wherein the modulation code generator comprises:

a first look up table for receiving the values of the left and right pixels as an input address, and outputting a corresponding justification value; and

a second look up table for receiving the value of the center pixel as an input address, and outputting a corresponding pulse width value.

15. The laser print apparatus of claim 1, wherein the modulation code generator is configured to generate the pulse width value based on the values of the left pixel, center pixel, and right pixel.

16. A method for generating modulation data for modulating a laser in a laser print apparatus, the method comprising:

rendering data to be printed into a multi-bit image including a plurality of pixels, each pixel represented by a multi-bit value;

examining the values of first, second, and third pixels that are correspondingly positioned at three sequential positions in the multi-bit image;

generating a first pulse width value based on the value of the second pixel; and

generating a first justification value based on the values of the first pixel and the third pixel.

17. The method of claim 16, wherein the laser is turned on and off at times corresponding to the first justification value, and remains on for a time period corresponding to the first pulse width value.

18. The method of claim 16, wherein the first justification value is a 2-bit value representing one of left justify, right justify, split justify, and center justify.

19. The method of claim 16, and further comprising:

providing at least one look up table that associates pixel values with pulse width values and justification values, and wherein the first pulse width value and the first justification value are generated by providing the values of the first, second, and third pixels as an input address to the at least one look up table.

20. The method of claim 19, wherein the at least one look up table provides a linear mapping between pixel values and pulse width values.

21. The method of claim 19, wherein the at least one look up table provides a non-linear mapping between pixel values and pulse width values.

22. A laser print apparatus comprising:

a memory for storing an image including a plurality of pixels, each pixel represented by a multi-bit value;

a first modulation code generator for generating a pulse width value for each pixel in the image based on the multi-bit value for the pixel;

a second modulation code generator for generating a justification value for each pixel in the image based on the multi-bit values of adjacent pixels; and

a laser print engine for forming an image on media based on the pulse width values and the justification values.