Dispersion-based technique for modulating pixels of a digital display panel

• US 6,175,355 B1
• Filed: 07/11/1997
• Issued: 01/16/2001
• Est. Priority Date: 07/11/1997
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Reddy, Dayakar Chandram
• Primary Examiner(s): CHANG, KENT WU
• Application Number:
  US08/893,872
• Time in Patent Office: 1,285 Days
• Field of Search: 345/147, 345/148, 345/149, 345/58, 345/89, 345/99
• US Class Current: 345/691
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals

Abstract

A technique for modulating pixels of a display panel for forming an image. Each pixel has an associated pixel frame, which is a period of time during which the pixel is modulated to achieve an appropriate greyscale level for the pixel. Each pixel frame includes a plurality of sub-frames. During each of the sub-frames, the pixel is placed in ‘on’ condition or in an ‘off’ condition according to a selected one of a plurality of predetermined greyscale sequences. Each greyscale sequence corresponds to a greyscale level for the pixel frame. A display frame is formed when each pixel in the display is appropriately modulated according to an image to be displayed. The displayed image is continually updated by displaying a sequence of display frames. The display panel is divided into blocks of sixteen pixels arranged in a four-by-four array. The greyscale sequences for pixels in a block are offset from one another by various numbers of sub-frames. This offset is termed pixel dispersion. The pixel blocks are grouped in four-by-four arrays of sixteen pixel blocks. Greyscale sequences for modulating the pixels in a block are offset from sequences for pixels in other blocks in the array by various numbers of sub-frames. This offset is termed block dispersion. Multiple arrays of blocks are updated in an identical manner to form a complete display panel.

Claims

1. A method of displaying a display image on a display panel having a plurality of pixels arranged in row and columns, the method comprising steps of:

a. dividing the display panel into first and second groups of pixels;

b. assigning a pixel modulation sequence to each pixel of the first and second groups according to the display image;

c. assigning pixel offset values to each pixel of the first and second groups;

d. assigning group offset values to each of the first and second groups; and

e. modulating each pixel of the display according to the pixel modulation sequence assigned to the pixel wherein the pixel modulation sequence is offset by an amount equal to a sum of the pixel offset value assigned to the pixel and the group offset value assigned to the group which includes the pixel.

2. The method according to claim 1 wherein the first and second groups are each an arrangement of rows and columns of adjoining pixels.

3. The method according to claim 1 wherein the first and second groups include an equal number of pixels and wherein each pixel in the first group corresponds to a pixel in the second group and wherein corresponding pixels are assigned an equal pixel offset value.

4. The method according to claim 1 wherein the first and second groups include an equal number of pixels positioned in a same arrangement and wherein each pixel in the first group corresponds to a pixel in the second group having a same position in the arrangement and wherein corresponding pixels are assigned an equal pixel offset value.

5. A method of displaying a display image on a display panel having a plurality of pixels arranged in row and columns, the method comprising steps of:

a. dividing the display panel into a plurality of groups of pixels, wherein each group includes a plurality of adjoining pixels;

b. assigning a pixel modulation sequence to each of a plurality of grey levels to be displayed during a display frame;

c. assigning one of the plurality of grey levels to each pixel according to the display image;

d. assigning one of a first plurality of offset values to each pixel of the display;

e. assigning one of a second plurality of offset values to each group of pixels; and

f. modulating each pixel of the display according to the pixel modulation sequence assigned to the grey level for the pixel wherein the pixel modulation sequence is offset by an amount equal to a sum of the offset value of the first plurality of offset values assigned to the pixel and the offset value of the second plurality of offset values assigned to the group which includes the pixel.

6. The method according to claim 5 wherein each group is an arrangement of rows and columns of adjoining pixels.

7. The method according to claim 5 wherein each group includes a same number of pixels and wherein each pixel in each group corresponds to a pixel in each other group and wherein corresponding pixels are assigned a same offset value of the first plurality.

8. The method according to claim 5 wherein each group includes a same number of pixels positioned in a same arrangement and wherein each pixel in each group corresponds to a pixel in each other group having a same position in the arrangement and wherein corresponding pixels are assigned a same offset value of the first plurality.

9. An apparatus for displaying a display image on a display panel having a plurality of pixels arranged in row and columns, the apparatus comprising:

a. a pixel counter for forming a pixel count value having upper bits and lower bits, wherein the pixel counter is incremented for each pixel in a row;

b. a line counter for forming a line count value having upper bits and lower bits, wherein the line counter is incremented when the pixel count value reaches a maximum count;

c. a first memory store for storing a plurality of block dispersion values wherein an appropriate one of the block dispersion values is selected according to a block identified by the upper bits of the pixel count value and by the upper bits of the line count value;

d. a first adder coupled to add the lower bits of the pixel count value and the lower bits of the line count value in concatenation to the selected dispersion value for forming a first sum; and

e. a second memory store for storing a plurality of pixel dispersion values wherein an appropriate one of the pixel dispersion values is selected according to the first sum.

10. The apparatus according to claim 15 further comprising:

a. a second adder coupled to add the selected pixel dispersion value to a value representative of a current sub-frame for a display frame for forming a second sum; and

b. a third memory store for storing a plurality of modulation sequences, each modulation sequence corresponding to a grey level for a pixel identified by the pixel count value and line count value, wherein an appropriate one of the modulation sequences is selected according to the display image and wherein an appropriate element of the selected sequence is selected according to the second sum.