问题
I was wondering what is the best way to convert a 24-bit RGB color (8 bits per color) into an 8-bit color (2bits Blue, 3 Green, 3 Red). I'd like C code for doing this.
回答1:
8 bit RGB is normally an indexed (palettized) color format, see Palette (computing).
The way you described it though, getting 8 bpp out of 24 bpp is pretty straightforward - you would need to strip least significant bits and merge the bits into single byte value, per pixel. AFAIK it is not a standard or well-known pixel color representation.
回答2:
Not in C but in javascript.
encodedData = (Math.floor((red / 32)) << 5) + (Math.floor((green / 32)) << 2) + Math.floor((blue / 64));
https://stackoverflow.com/a/25258278/2130509
回答3:
To convert 8bit [0 - 255] value into 3bit [0, 7], the 0 is not a problem, but remember 255 should be converted to 7, so the formula should be Red3 = Red8 * 7 / 255.
To convert 24bit color into 8bit (RRRGGGBB),
8bit Color = (Red * 7 / 255) << 5 + (Green * 7 / 255) << 2 + (Blue * 3 / 255)
来源：https://stackoverflow.com/questions/7657704/how-to-convert-24-bit-rgb-to-8-bit-rgb