Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1999-03-30
2001-06-26
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
15, 15
Reexamination Certificate
active
06252585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image display system, and device and method for using this system.
2. Description of the Related Art
In image display systems, it is desirable to reduce the amount of information that is needed to represent images. One technique to achieve this is the use of a color look-up table (CLUT) which is used particularly in systems that generate computer graphics images. In this case, one represents the color value of each pixel in an image by an index value that points to a color value stored in the CLUT. When a color value is needed, the index value is used to retrieve the color value from the CLUT.
The palette of colors that is available in the CLUT is preferably much smaller than the total number of conceivable color values. Thus, the amount of information needed to represent an index value is smaller than the amount of information that is needed to represent an arbitrary color value.
Of course, the price of this is that the representation by index values of an arbitrary original image is only approximate: there will be differences between the color values of the original image and the representation. When such a representation is used to display the arbitrary image, the differences will show up as high frequency noise. In addition, there may be systematic color errors (low frequency noise), but these can be eliminated by dithering techniques.
In some display systems, in particular, in video or television display systems, colors for display are represented by YUV values, that is, a luminance component Y and color difference components UV, as standardized by the CCIR. When YUV values are used, a higher spatial resolution is preferably used for the Y component than for the UV components. Typically, separate Y values are used for different pixels, whereas the UV components are the same for pairs of adjacent pixels.
The YUV components corresponding to different colors may be stored in a CLUT, but of course this is merely a matter of representation; it does not affect the noise caused by using a CLUT.
SUMMARY OF THE INVENTION
It is an object of the invention to reduce the amount of visible noise.
The display system according to one aspect of the invention is, comprises a cascade of an image source, an index determination element, a lookup table unit and an output unit, successively, the image source producing source color values, the index determination element selecting index values as a function of the source color values, the index values pointing to LUT color values stored in the lookup table unit, the output unit deriving output color values from LUT color values read from the lookup table unit under selection from the index values, each output color value corresponding to a pixel, a first component of the output color values being output in common for at least two pixels and a second component being output separately for each of these at least two pixels, so that there is a space of possible combinations of index values for these at least two pixels which combinations all result in substantially the same first component of the output color value, the index values in at least one combination from this space pointing to substantially different LUT color values, wherein the index determination element uses selection from this space to minimize an error in the second component of the output color values for the at least two pixels. The idea behind this aspect of the invention is that one makes use of the knowledge that a first component of the color values, such as the U or V component, is output at a lower spatial resolution than a second component of the color values, such as the Y component. Hence, without causing larger noise, one can select index values without minimizing the errors in the first component (e.g., U or V) at the higher resolution, as long as the error in the actual component that is output at the lower resolution is substantially minimized (substantially meaning, for example that the error is less than a factor of say 2 times the minimum possible error). According to this aspect of the invention, the additional selection freedom is used to get a closer approximation of the second component (e.g., Y). This is done by selecting an index value that minimizes the errors in the second component among a larger space of possible index values.
In an embodiment of the display system of the invention, the color values in the CLUT contain a Y field, a U field and a V field, used to control the color components on a displayed image according to the YUV standard, the first component being the U and/or V component and the second component being the Y component.
In a further embodiment of the display system according to the invention, the U and/or V component of the LUT color value for only every second pixel is output. In this case, the index values for the other pixels, for which neither the U nor the V component is output, are selected to minimize the error in the Y component, for example, by ensuring that the average of the Y components of each pair of a “second” pixel and an “other” pixel matches the Y component of the corresponding source color value or values. Thus, the space of index values is always the same and it is possible to select from the set of combinations of index values by lookup from a table instead of a more time-consuming search.
In a further embodiment of the display system of the invention, the index values are determined from color values that contain RGB fields. Thus, a conventional graphics image source may be used.
In another embodiment of the invention, the transfer unit ignores the first component of every second pixel and the index value for the second pixels being determined as a function of the second component of the pixel values only. In this way, little computational overhead is needed to determine the index values.
REFERENCES:
patent: 5227863 (1993-07-01), Bilbrey
patent: 5611030 (1997-03-01), Strokes
patent: 5940067 (1999-08-01), Greene
patent: 5943058 (1999-08-01), Nagy
patent: 6043804 (2000-03-01), Greene
Pol Evert J. D.
Van Splunter Marinus
Gross Russell
Luu Matthew
Sajous Wessner
U.S. Philips Corporation
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