SDL_GetRGB (3) Linux Manual Page
SDL_GetRGB – Get RGB values from a pixel in the specified pixel format.
Synopsis
#include "SDL.h" void SDL_GetRGB(Uint32 pixel, SDL_PixelFormat *fmt, Uint8 *r, Uint8 *g, Uint8 *b);
Description
Get RGB component values from a pixel stored in the specified pixel format. This function uses the entire 8-bit [0..255] range when converting color components from pixel formats with less than 8-bits per RGB component (e.g., a completely white pixel in 16-bit RGB565 format would return [0xff, 0xff, 0xff] not [0xf8, 0xfc, 0xf8]).