ajrobb
13th January 2011, 13:24
I still choose to watch fullscreen CRT as I haven't seen a panel TV I like. Shops might not do themselves any favours with their displays but I quickly get distracted by digital artefacts and colour banding in particular. OK, so it is mainly a problem on 'clean' computer generated graphics, but smooth backgrounds just aren't smooth. I suspect a lot of the problem is with the 8-bit luminance resolution.
The MPEG DCT averages 64x8-bit samples into a few 11-bit coefficients (because the square root of 64 is 8 giving 3 extra bits). The IDCT combines up to 64 11-bit coefficients into each 8-bit value but the maths says the output should be between 11 and 14 bits. I suspect decoders simply truncate these values to 8-bit values of luminance and chrominance.
HDMI 1.3 supports deep colour but this doesn't seem well supported yet. However, I think it is possible to improve a 24-bit RGB display in software to give much finer luminance resolution. Basically, blue has a luminance factor of 0.114 (from memory), so can be adjusted to give very fine luminance control. Blue level only has to be accurate when averaged over 4 pixels but you can play about with individual pixels. Red has a higher luminance than blue, so can be used for coarser adjustments. By adjusting the RGB levels, the luminance can be displayed to better than 11 bits on a consumer 24-bit RGB screen.
The MPEG DCT averages 64x8-bit samples into a few 11-bit coefficients (because the square root of 64 is 8 giving 3 extra bits). The IDCT combines up to 64 11-bit coefficients into each 8-bit value but the maths says the output should be between 11 and 14 bits. I suspect decoders simply truncate these values to 8-bit values of luminance and chrominance.
HDMI 1.3 supports deep colour but this doesn't seem well supported yet. However, I think it is possible to improve a 24-bit RGB display in software to give much finer luminance resolution. Basically, blue has a luminance factor of 0.114 (from memory), so can be adjusted to give very fine luminance control. Blue level only has to be accurate when averaged over 4 pixels but you can play about with individual pixels. Red has a higher luminance than blue, so can be used for coarser adjustments. By adjusting the RGB levels, the luminance can be displayed to better than 11 bits on a consumer 24-bit RGB screen.