Adaptive noise reduction for digital display panels
A plasma display panel is a pure linear display and does not provide a non-linear gamma behavior like a CRT so that an artificial gamma function has to be applied to the signal in digital form. This gamma function increases the quantization steps in the dark areas whereas the quantization steps will be reduced in the luminous areas. The basic idea is to apply an adaptive noise filtering after the gammatization process. The adaptive filtering is a specific filtering which is adapted to the gammatization quantization noise. In other words, the filtering will be maximum for dark areas and its efficacy will be automatically decreased when the luminance of the area is increasing.
1. Method for reducing quantization error during video level signal processing for a display device with digitally driven pixels, comprising:
digitally filtering a signal charged with said quantization error with a digital filter having a plurality of filter coefficients, said signal including a video level for each pixel of said display device, and
varying at least one of said filter coefficients of the filter in dependence on the video level for a current pixel by stronger filtering a lower video level for said pixel while less filtering or not filtering a higher video level for said pixel to reduce quantization error in the lower video level;
wherein said filtering includes one and/or two dimensional median filtering.
2. Method according to claim 1 , wherein said filtering includes one and/or two dimensional low pass filtering.
3. Method according to claim 1 , wherein a decreased value for the filter coefficient is used for a pixel with increased luminance.
4. Method according to claim 1 , wherein the spatial dimension and/or the temporal direction of said digital filter varies with the video level of a current pixel.
5. Method according to claim 1 , wherein, in case of a low pass filter, the coefficients are given by
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with a 0 =1 and with a i =f i (x 0 , x i ).
6. Method according to claim 5 , wherein, the function is the following:
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7. Device for reducing quantization error during video level signal processing for a display device with digitally driven pixels, comprising:
digital filter means for digitally filtering a video signal charged with said quantization error, said filter means having a plurality of filter coefficients, and said signal including a video level for each pixel of said display device, and
a controlling means connected to said digital filter means for varying at least one of said filter coefficients in dependence on the video level for a current pixel by stronger filtering a lower video level for said pixel while less filtering or not filtering a higher video level for said pixel to reduce noise in the lower video level;
wherein said digital filter means includes a one and/or two dimensional median filter.
8. Device according to claim 7 , wherein said digital filter means includes one and/or two dimensional low pass filter.
9. Device according to claim 7 , wherein the value of a filter coefficient is decreasable by said controlling means when the luminance of a current pixel increases.
10. Device according to claim 7 , wherein the spatial dimension and/or the temporal direction of a filter of said digital filter means is variable with the video level of a current pixel by said controlling means.