Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2001-12-10
2004-03-30
Bella, Matthew C. (Department: 2676)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S596000, C345S605000, C345S597000, C345S600000, C345S690000, C345S694000, C345S695000, C358S518000, C358S519000, C358S520000
Reexamination Certificate
active
06714206
ABSTRACT:
BACKGROUND
The described technology relates to setting intensity levels for sub-pixels of displays with overlapping logical pixels.
Active matrix liquid crystal displays have become very popular for computer monitors and televisions. These liquid crystal displays typically have pixels that each contains a red, a green, and a blue stripe. These pixels are referred to as an “RGB stripe pixel.” Each stripe of a pixel is referred to as a “sub-pixel.” The image quality of these liquid crystal displays varies depending on the density of pixels and the number of intensity levels supported by the display. These liquid crystal displays typically use either 6 bits per sub-pixel or 8 bits per sub-pixel to represent intensity levels. The number of bits per sub-pixel is referred to as the “pixel depth.” With 6 bits per pixel, 262,144 colors can be displayed, and with 8 bits per pixel, almost 17 million colors can be displayed. Although the quality of images produced from a display that uses 8 bits per pixel is much higher than from a display that uses 6 bits per pixel, the cost of a display that uses 8 bits per pixel is significantly higher.
Spatial dithering has traditionally been used to improve the image quality of displays that use lower depth pixels. Spatial dithering typically involves mapping intensity values of a higher depth (e.g., 8 bits per sub-pixel) to intensity values of a lower depth (e.g., 6 bits per sub-pixel). When mapping from 8 to 6 bits per sub-pixel, the range of intensity values is reduced from 256 to 64. In such a case, four different 8-bit intensity values map to each 6-bit intensity value. For example, the 8-bit intensity values of 32, 33, 34, and 35 may map to a 6-bit intensity value of 8. The mapping from an 8-bit intensity value to a 6-bit intensity value is typically performed by dividing the 8-bit intensity value by 4, which leaves a remainder of 0 to 3. The remainder represents a loss of image quality that results from the mapping. With spatial dithering, the display may be divided into super-pixels comprising 4 pixels each, and the intensity values of the pixels within a super-pixel are adjusted based on the remainder. For example, if the 8-bit intensity value is 33, then the 6-bit intensity value is 8 with a remainder of 1. Because the remainder is 1, one of the pixels of a super-pixel is set to an intensity value of 9, and the other three pixels of the super-pixel are set to an intensity value of 8. Since the pixels are small and close together, the eye perceives the dithered super-pixel with one intensity value of 9 and three intensity values of 8 as very similar to the intensity value of 33 with a depth of 8 bits.
In order to improve the image quality of a liquid crystal display that displays color with a lower depth than can be provided to the display, various other dithering techniques have been used. One such class of dithering techniques is referred to as “frame rate control” (“FRC”). Frame rate control techniques use both “temporal dithering” and “spatial dithering,” which can take advantage of the slow response time of liquid crystals to small changes in applied voltage. Temporal dithering refers to dithering from one frame to the next as opposed to dithering within a single frame. (A typical display may display 30 or 60 frames per second.) With frame rate control, a single pixel may have its intensity value varied from one frame to the next to account for the loss of depth. For example, if the 8-bit intensity value of 33 is mapped to a 6-bit intensity value of 8 with a remainder of 1, then a pixel may have its intensity value set to 9 during every fourth frame and set to 8 during the remaining 3 frames. Thus, temporal dithering tends to approximate the 8-bit intensity value over time, rather than over space. Frame rate control uses a combination of dithering techniques by defining a super-pixel or pattern of pixels to indicate which pixels should have their intensity levels increased from one frame to the next. For example, if a super-pixel comprises 4 pixels, then an 8-bit intensity value of 33 can be approximated by setting the intensity value of the first pixel of the super pixel to 9 and setting the intensity value of all other pixels to 8 during the first frame, by setting the intensity value of the second pixel of the super-pixel to 9 and setting the intensity value of all other pixels to 8 during the second frame, and so on. Thus, the super-pixel approximates the 8-bit intensity value using both temporal and spatial dithering.
Because the eye can differentiate the colors of a green and red to a greater degree than the color blue, different types of striping techniques have been developed. One such technique, referred to as a “split stripe,” divides the green and the red stripe of an RGB striped pixel into two, leaving 5 sub-pixels: 2 vertically aligned green sub-pixels, 2 vertically aligned red sub-pixels and 1 blue sub-pixel positioned in between the red and the green sub-pixels. The image quality can be improved by independently setting each red and green sub-pixel within a pixel to a different intensity level. Another technique, referred to as “Pentile tiling,” exchanges the position of a red and green sub-pixel of the split stripe pixel so that sub-pixels of the same color are no longer vertically aligned but are instead diagonally aligned. Another form of Pentile tiling is to replace the rectangular striped sub-pixels with different shaped sub-pixels.
FIG. 1
is a diagram illustrating a form of Pentile tiling. Pixel
100
includes 5 sub-pixels
101
-
105
. Sub-pixels
101
and
103
display the color red, sub-pixels
102
and
104
display the color green, and sub-pixel
105
displays the color blue.
When the Pentile pixels of
FIG. 1
are arranged in a matrix, the colors are usually specified using logical pixels, rather than physical pixels. A logical pixel is generally defined as a group of adjacent sub-pixels that may include sub-pixels from different physical pixels. A logical pixel is typically a center sub-pixel and its surrounding sub-pixels. The intensity value of a sub-pixel of a display is generally set based on intensity values of its surrounding logical pixels that are weighted according to their location relative to the sub-pixel.
FIG. 2
illustrates a logical pixel of a Pentile matrix of pixels. The pixel
100
in
FIG. 1
illustrates what is commonly referred to as a physical pixel. The Pentile matrix
200
shows 6 physical pixels
201
-
206
that are each centered on a blue sub-pixel. A logical pixel of a Pentile matrix, in contrast, may be centered on each red sub-pixel and each green sub-pixel. A logical pixel of the Pentile matrix may be defined as a center sub-pixel, the adjacent blue sub-pixel, and the four adjacent sub-pixels with a color different from the center sub-pixel. Logical pixel
207
is illustrated with a bold line drawn around it. The center of the logical pixel is red sub-pixel
208
, and it is adjacent to the blue sub-pixel
209
and to the four green sub-pixels
210
-
213
. Thus, the sub-pixels
208
-
213
form logical pixel
207
. Green sub-pixels
210
-
213
are centers of logical pixels that each include sub-pixel
208
.
FIGS. 3-6
illustrate logical pixels of the Pentile matrix that overlap a common sub-pixel. In
FIG. 3
, logical pixel
214
is centered on green sub-pixel
210
. As can be seen, logical pixel
214
includes red sub-pixel
208
. Thus, logical pixel
207
and logical pixel
214
overlap. (Actually, logical pixels
207
and
214
each contain sub-pixels
208
,
209
, and
210
in common.) In
FIGS. 4-6
, logical pixels
221
,
228
, and
235
are illustrated as overlapping the center sub-pixel
208
of logical pixel
207
. Thus, sub-pixel
208
is included in logical pixels
207
,
214
,
221
,
228
, and
235
.
According to one technique, when generating the intensity value for a sub-pixel of a logical pixel, the intensity values of the logical pixels that include that sub-pixel are combined. Each red sub-pixel and green sub-pixel is included in 5 logical pixels, and each bl
Adams Dale
Martin Russel A.
Siemens Duane
Steemers Hugo
Bella Matthew C.
Perkins Coie LLP
Rahmjoo Manucher
Silicon Image
LandOfFree
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