Provided by: allegro5-doc_5.0.11-2_all 

NAME
al_color_rgb_to_cmyk - Allegro 5 API
SYNOPSIS
#include <allegro5/allegro_color.h>
void al_color_rgb_to_cmyk(float red, float green, float blue,
float *cyan, float *magenta, float *yellow, float *key)
DESCRIPTION
Each RGB color can be represented in CMYK with a K component of 0 with the following formula:
C = 1 - R
M = 1 - G
Y = 1 - B
K = 0
This function will instead find the representation with the maximal value for K and minimal color
components.
SEE ALSO
al_color_cmyk(3alleg5), al_color_cmyk_to_rgb(3alleg5)
al_color_rgb_to_cmyk(3all... Allegro reference manual()