Extracting rgb color components from integer value

Question

Hi, if there is an integer value, eg. 86 then how can i extraact the r,g,b components from this integer value....? I am working on Visual C++ 2008 express edition. Thanks..

Answer 1

Usually (and I repeat usually, since you don't specify much in your question) a color is packed in a 4-bytes integer with RGBA components.

What you need to do it so mask and shift, for example:

int color = 0xRRGGBBAA;

u8 red = (color & 0xFF000000) >> 24;
u8 green = (color & 0x00FF0000) >> 16;
u8 blue = (color & 0x0000FF00) >> 8;

This assumes the kind of encoding I specified, but can me modified according to yours.

EDIT: in your example you spoke about a 0-255 value. It is not clear if compnents are 2bit sized (4 intensity values per component).

In that case the approach still remains the same but you will have just few colors:

u8 color = 86;

// so you take 2 bits and multiply by 64 to possibly have intensities: 0, 64, 128, 192
u8 red = ((color & 0xC0) >> 6) * 64; 
u8 green = ((color & 0x30) >> 4) * 64;
u8 green = ((color & 0x0C) >> 2) * 64;

EDIT2: Maybe your colors are indexed with palette, in that case you should have an array that stores the palette itself and the byte you read from the file should be the index of a color stored somewhere else.

Answer 2

Normally you want to create a color from three components using the RGB macro. Assuming the value you have is in the same format, you can pull it back apart into the individual pieces with GetRValue, GetGValue and GetBValue.