RGB Feature Scaling in C

Feature scaling is used to scale values to a range between 0 and 1. The equation is n = i + (i - min(x)/(max(x) - min(x))), where i is the input value to be normalized, and x is the array of values (0-255 in this context). Since RGB values deal with a min of 0 and a max of 255 this makes the equation n = i / 255.

The context for this is because my dasteroids project uses the allegro game libraries, and the function I use to create an ALLEGRO_COLOR is al_map_rgb_f, which takes three floats from 0 to 1.

If I want to create the color red then the corresponding call would be al_map_rgb_f(1.0, 0.0, 0.0);, but if I want to create the color orange (255, 127, 0), I would need to normalize 127. Using the above equation, the normalized value is 127/255, which is 0.498039.

The implementation in C looks like the following.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, const char* argv[])
{
    if (argc < 2) {
        printf("Usage: ./main <0-255>\n");
        exit(-1);
    }

    char *endptr;
    float n = strtof(argv[1], &endptr);

    float normalized = n / 255.0;

    printf("%f normalized: %f\n", n, normalized);

    return 0;
}

and when running ./main 42, we get 42.000000 normalized: 0.164706.

Tags:

#c #feature-scaling