In commonly owned United States Patent Applications: (1) U.S. patent application Ser. No. 09/916,312 entitled “ARRANGEMENT OF COLOR PIXELS FOR FULL COLOR IMAGING DEVICES WITH SIMPLIFIED ADDRESSING,” filed Jul. 25, 2001 and issued as U.S. Pat. No. 6,903,754 (“the '754 patent”); (2) U.S. patent application Ser. No. 10/278,353 entitled “IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUB-PIXEL ARRANGEMENTS AND LAYOUTS FOR SUB-PIXEL RENDERING WITH INCREASED MODULATION TRANSFER FUNCTION RESPONSE,” filed Oct. 22, 2002 and published as U.S. Patent Publication No. 2003/0128225 (“the '225 application”); (3) U.S. patent application Ser. No. 10/278,352 entitled “IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUB-PIXEL ARRANGEMENTS AND LAYOUTS FOR SUB-PIXEL RENDERING WITH SPLIT BLUE SUB-PIXELS,” filed Oct. 22, 2002 and published as U.S. Patent Publication No. 2003/0128179 (“the '179 application”); (4) U.S. patent application Ser. No. 10/243,094 entitled “IMPROVED FOUR COLOR ARRANGEMENTS AND EMITTERS FOR SUB-PIXEL RENDERING,” filed Sep. 13, 2002 and published as U.S. Patent Publication No. 2004/0051724 (“the '724 application”); (5) U.S. patent application Ser. No. 10/278,328 entitled “IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUB-PIXEL ARRANGEMENTS AND LAYOUTS WITH REDUCED BLUE LUMINANCE WELL VISIBILITY,” filed Oct. 22, 2002 and published as U.S. Patent Publication No. 2003/0117423 (“the '423 application”); (6) U.S. patent application Ser. No. 10/278,393 entitled “COLOR DISPLAY HAVING HORIZONTAL SUB-PIXEL ARRANGEMENTS AND LAYOUTS,” filed Oct. 22, 2002 and published as U.S. Patent Publication No. 2003/0090581 (“the '581 application”); (7) U.S. patent application Ser. No. 10/347,001 entitled “IMPROVED SUB-PIXEL ARRANGEMENTS FOR STRIPED DISPLAYS AND METHODS AND SYSTEMS FOR SUB-PIXEL RENDERING SAME,” filed Jan. 16, 2003, and published as Patent Publication No. 2004/0080479 (“the '479 application”); novel sub-pixel arrangements are therein disclosed for improving the cost/performance curves for image display devices and herein incorporated by reference.
These improvements are particularly pronounced when coupled with sub-pixel rendering (SPR) systems and methods further disclosed in those applications and in commonly owned United States Patent Applications: (1) U.S. patent application Ser. No. 10/051,612 entitled “CONVERSION OF A SUB-PIXEL FORMAT DATA TO ANOTHER SUB-PIXEL DATA FORMAT,” filed Jan. 16, 2002 and published as U.S. Patent Publication No. 2003/0034992 (“the '992 application”); (2) U.S. patent application Ser. No. 10/150,355 entitled “METHODS AND SYSTEMS FOR SUB-PIXEL RENDERING WITH GAMMA ADJUSTMENT,” filed May 17, 2002 and published as U.S. Patent Publication No. 2003/0103058 (“the '058 application”); (3) U.S. patent application Ser. No. 10/215,843 entitled “METHODS AND SYSTEMS FOR SUB-PIXEL RENDERING WITH ADAPTIVE FILTERING,” filed Aug. 8, 2002 and published as U.S. Patent Publication No. 2003/0085906 (“the '906 application”); (4) U.S. patent application Ser. No. 10/379,767 entitled “SYSTEMS AND METHODS FOR TEMPORAL SUB-PIXEL RENDERING OF IMAGE DATA” filed Mar. 4, 2003 and published as U.S. Patent Publication No. 2004/0196302 (“the '302 application”); (5) U.S. patent application Ser. No. 10/379,765 entitled “SYSTEMS AND METHODS FOR MOTION ADAPTIVE FILTERING,” filed Mar. 4, 2003 and issued as U.S. Pat. No. 7,167,186 (“the '186 patent”); (6) U.S. patent application Ser. No. 10/379,766 entitled “SUB-PIXEL RENDERING SYSTEM AND METHOD FOR IMPROVED DISPLAY VIEWING ANGLES” filed Mar. 4, 2003 and issued as U.S. Pat. No. 6,917,368 (“the '368 patent”) (7) U.S. patent application Ser. No. 10/409,413 entitled “IMAGE DATA SET WITH EMBEDDED PRE-SUBPIXEL RENDERED IMAGE” filed Apr. 7, 2003, and published as Patent Publication No. 2004/0196297 (“the '297 application”) which are hereby incorporated herein by reference.
The accompanying drawings, which are incorporated in, and constitute a part of this specification illustrate exemplary implementations and embodiments of the invention and, together with the description, serve to explain principles of the invention.
Reference will now be made in detail to implementations and embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
As also shown, each subpixel is connected to a column line (each driven by a column driver 110) and a row line (e.g. 112 and 114). In the field of AMLCD panels, it is known to drive the panel with a dot inversion scheme to reduce crosstalk or flicker.
In several co-pending applications, e.g., the applications entitled “DISPLAY PANEL HAVING CROSSOVER CONNECTIONS EFFECTING DOT INVERSION” now published as US Patent Publication No. 2004/02463281 and “SYSTEM AND METHOD OF PERFORMING DOT INVERSION WITH STANDARD DRIVERS AND BACKPLANE ON NOVEL DISPLAY PANEL LAYOUTS,” now published as US Patent Publication No. 2004/0246381 there are disclosed various techniques that attempt to solve the dot inversion problem on panels having even-modulo subpixel repeating groups.
Although the above solutions possibly introduce visual effects that, if noticeable, might be detracting, these solutions share one common trait—the visual effects occur at places (e.g., chip boundaries, crossovers, etc) that are well known at the time of panel manufacture. Thus, it is possible to plan for and correct (or at least abate) these effects, so that it does not negatively impact the user.
In such cases, the panels at issue exhibit a visual image distortion that might be described as a “fixed pattern noise” in which the Electro-Optical (EO) transfer function for a subset of the pixels or subpixels is different, perhaps shifted, from another subset or subsets. This fixed pattern noise, if uncompensated, may cause an objectionable image if the differences are large. However, as disclosed herein, even these large differences may be advantageous in reducing quantization noise artifacts such as false contours, usually caused by insufficient grey scale depth.
Another source of the fixed pattern noise that is usually inadvertent and/or undesirable results from the differences in subpixel electrical parasitics. For example, the difference in parasitics may be the result of shifting the position or size of the Thin Film Transistor (TFT) or storage capacitor in an active matrix liquid crystal display (AMLCD). Alternatively, the fixed pattern noise may be deliberate on the part of the designer, such as adjusting the aperture ratio of the subpixels, or the transmittance of a color or polarizer filter. The aperture ratio may be adjusted using any single or combination of adjustments to the design of the subpixels, most notably the ‘black matrix’ used in some LCD designs. The techniques disclosed here may be used on any suitable pixelated or subpixelated display (monochrome or color).
In one embodiment, these two different sources of fixed pattern noise may give rise to two forms of EO difference. One form might be a linear shift, as might happen when the aperture ratio is different for the subsets. The other is a shift in the shape of the EO curve, as might happen in a difference of parasitics. Both may be adjusted via quantizing look-up tables (“LUTs”) storing bit depth values, since the LUTs are a complimentary (inverse) function.
Since the pattern noise is usually predictable and/or measurable, one possible embodiment is to provide separate quantizers for each subset of pixels or subpixels, matched to the EO transfer function of each subset. One suitable quantizer in a digital system could be implemented as a look-up table (LUT) that converts a greater bit depth value to a smaller bit depth value. The large bit depth value may be in a subpixel rendering or scaling system. The large bit depth value may be in a linear luminance space or any arbitrary space encoding.
Having separate LUTs not only compensates for the fixed pattern noise, but since each combination of subpixel subset and LUT quantizes (changes output) at different inputs, the effective grey scale of the display system is increased. The subsets need not be quantizing exactly out of step, nor uniformly out of step, for improvement to be realized, though it helps if they are. The number of subsets may be two or more. More subsets increases the number of LUTs, but also increases the benefit of the quantization noise reduction and increased grey scale reproduction since each subset would be quantizing at different input levels.
Therefore it may be advantageous to deliberately introduce fixed pattern noise, using two or more subsets of EO transfer functions per subpixel color, preferably distributed evenly across the entire display. Since green is usually responsible for the largest percentage of luminance perception, having multiple subsets of green will increase the luminance grey scale performance. Having two or more subsets in red further increases the luminance grey scale performance, but to a lesser degree. However, having increases in any color, red, green, or blue, increases the number of colors that may be represented without color quantization error.
The fixed pattern noise may be large or small amplitude. If small, it may not have been visible without the matched quantizers; but the improvement in grey scale would still be realized with the matched quantizers. If the amplitude is large, the noise may be very visible, but with the matched quantizers, the noise is canceled, reduced to invisibility and the grey scale improved at the same time. The use of multiple quantizers may be combined with high spatiotemporal frequency noise added to the large bit depth values to further increase the performance of the system, the combination of the two providing greater performance than either alone. Alternatively, the multiple quantizers may be in combination with temporal, spatial, or spatio-temporal dithering.
The advantage of reduction of quantization noise is considerable when a system uses lower grey scale drivers than the incoming data provides. However, as can be seen in
Examining
An incoming signal 810 with a given bit depth is converted to a greater bit depth and is simultaneously impressed with the desired display system gamma curve by the incoming LUT 810. This is followed by any desired image processing step 850 such as subpixel rendering, scaling, or image enhancement. This is followed by a suitable means for selecting the appropriate LUT (812 or 814) for the given pixel or subpixel, herein represented as a demux circuit element 820. This element may be any suitable means known in the art. Each subset is then quantized by LUTs 812 and 814 to a lower bit depth matching that used by display driver chips 804 of the display device system. Each of these LUTs 812 and 814 has a set of paired numbers that are generated to serve as the inverse or complementary function of the matching EO curves 832 and 834 respectively. When these values are used to select the desired brightness or color levels of each subset, the resulting overall display system transfer curve 802 is the same as that of the incoming LUT 810. Following the output gamma compensation LUTs 812 and 814 is a means 826 for combining the results, herein represented as a mux, of the multiple LUTs 812 and 814 to send to the display drivers 804.
Special note should be taken of the nature of the EO curve difference and the desired behavior in the case of an even image field at the top of the value range. For example, in the case of a text based display where it is common to display black text on a white background, the even quality of the white background is highly desirable. In such a case, the brightness level of the darkest subset of pixels or subpixels will determine the highest level to which the brighter subsets will be allowed to proceed, given sufficient quantizer steps to equalize at this level. This may of necessity lead to lost levels above this nominally highest level, for the brighter subset(s). Another case might be handled differently, for example, for television images, the likelihood of an even image field at the top of the value range is reasonably low, (but not zero). In this case, allowing the top brightness of the brighter subset(s) to exceed that of the lowest subset may be acceptable, even desirable, provided that all levels below that are adjusted to be the same per the inventive method described herein.
It should also be noted that it may be desirable, due to different EO curves for different colors, that each color have its own quantizing LUT. There may be different EO subset within each color subset per the present invention. It may be desirable to treat each color differently with respect to the above choices for handling the highest level settings. For example, blue may be allowed to exhibit greater differences between subsets than green or red, due to the human vision system not using blue to detect high spatial frequency luminance signals.
Furthermore, it should be understood that this system may use more than two subsets to advantage, the number of LUTs and EO curves being any number above one. It should also be understood by those knowledgeable in the art, that the LUTs may be substituted by any suitable means that generates the same, or similar, output function. This may be performed as an algorithm in software or hardware that computes, or otherwise delivers, the inverse of the display subset EO curves. LUTs are simply the means of choice given the present state of art and its comparative cost structure. It should also be further understood, that while
The implementation, embodiments, and techniques disclosed herein work very well for liquid crystal displays that have different regions of subpixels having different EO characteristics—e.g. due to dot inversion schemes imposed on panels have an even number of subpixels in its repeating group or for other parasitic effects. It should be appreciated, however, that the techniques and systems described herein are applicable for all display panels of any different type of technology base—for example, OLED, EL, plasma and the like. It suffices that the differences in EO performance be somewhat quantifiable or predictable in order to correct or adjust the output signal to the display to enhance user acceptability, while at the same time, reduce quantizer error.
This application is a divisional of, and claims priority to, U.S. patent application Ser. No. 10/455,927 filed on Jun. 6, 2003, and issued as U.S. Pat. No. 7,209,105. U.S. Ser. No. 10/455,927 was published as US Patent Application Publication No. 2004/0246278 which is hereby incorporated by reference herein for all that it teaches The present application is related to commonly owned United States Patent Applications: (1) U.S. patent application Ser. No. 10/455,925 entitled “DISPLAY PANEL HAVING CROSSOVER CONNECTIONS EFFECTING DOT INVERSION” and published as U.S. Patent Publication No. 2004/0246213 (“the '213 application”); (2) U.S. patent application Ser. No. 10/455,931 entitled “SYSTEM AND METHOD OF PERFORMING DOT INVERSION WITH STANDARD DRIVERS AND BACKPLANE ON NOVEL DISPLAY PANEL LAYOUTS” and published as U.S. Patent Publication No. 2004/0246381 (“the '381 application”); (3) U.S. patent application Ser. No. 10/456,806 entitled “DOT INVERSION ON NOVEL DISPLAY PANEL LAYOUTS WITH EXTRA DRIVERS” and published as U.S. Patent Publication No. 2004/0246279 (“the '279 application”); (4) U.S. patent application Ser. No. 10/456,838 entitled “LIQUID CRYSTAL DISPLAY BACKPLANE LAYOUTS AND ADDRESSING FOR NON-STANDARD SUBPIXEL ARRANGEMENTS” and published as U.S. Patent Publication No. 2004/0246404 (“the '404 application”) and (5) U.S. patent application Ser. No. 10/456,839 entitled “IMAGE DEGRADATION CORRECTION IN NOVEL LIQUID CRYSTAL DISPLAYS,” and published as U.S. Patent Publication No. 2004/0246280 (“the '280 application”) which are hereby incorporated herein by reference.
Number | Date | Country | |
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Parent | 10455927 | Jun 2003 | US |
Child | 11739065 | Apr 2007 | US |