> I want to configure my X with 16 Bit on my IBook2 with aty128 for > running opengl with 1024x786 pixels. > > But after that, I saw, X felt back to 15 Bit and my screen was green. > > How can I fix it?
You can never fix 16-bit color. It is not possible to display any shade of grey while in 16-bit mode, excepting black and white. Look at the bits! I'll put the most-significant bit on the left. I'll pick a 6-bit green value, in binary. 001101 looks good. Now what do you want for 5-bit red and blue, 00110 or 00111? You get either this: r 001100011000110001100011000110... g 001101001101001101001101001101... b 001100011000110001100011000110... or you get this: r 001110011100111001110011100111... g 001101001101001101001101001101... b 001110011100111001110011100111... It doesn't work the other way either. You can't pick ANY 5-bit value and get a matching 6-bit value, except with black and white. With 5 bits, the space between values is 1/31 of the range. With 6 bits, the space between values is 1/63 of the range. Since 31 doesn't have any common factors with 63, the only pure grayscale values are black and white. Eeeew! Your only hope is to get lucky with broken D->A hardware, in which case you might be able to pretend you have a 15-bit display by setting the low green bit equal to the high green bit. Gross!
