enhancer/main.c

#define STB_IMAGE_IMPLEMENTATION
#define STB_IMAGE_WRITE_IMPLEMENTATION
#define STBI_FAILURE_USERMSG

#include "stb_image.h"
#include "stb_image_write.h"

/*
0 - balanced
1 - average of two largest channels, bias towards darker shades, use if unsure
2 - makes image brighter
3 - ??? (lots of banding so reduce strength)
*/
#define LUMINANCE_METHOD 1

/*
1 is the minimum, going below 1 makes surprising effects
the higher value the less effect it has
so when I say "reduce strength" I mean "increase the value"
*/
#define VIBRANCE_STRENGTH 1.5

/*
if a pixel goes below 0% or above 100% basically subtract the difference
so -10% becomes 10% and 110% becomes 90%
this was supposed to fix clipping but messes up colors (I remember I had in mind a fix but I don't remember it)

uncomment to enable
*/
//#define BETTER_CLAMP

const static inline int max(int a, int b) {
    return a > b ? a : b;
}

const static inline int max3(int a, int b, int c) {
    int ab = max(a, b);
    return ab > c ? ab : c;
}

const static inline int min(int a, int b) {
    return a < b ? a : b;
}

const static inline int min3(int a, int b, int c) {
    int ab = min(a, b);
    return ab < c ? ab : c;
}

#ifdef BETTER_CLAMP
const static inline int cdiff(int n, int min, int max) {
    if (n > max)
        return max - (n - max);
    else if (n < min) {
        return min + (min - n);
    }

    return n;
}

const static inline int clamp(int n, int min, int max) {
    return cdiff(n, min, max);
} // I don't know if const static inline was needed
#else
const static inline int clamp(int n, int min, int max) {
    return n > max ? max : (n < min ? min : n);
}

#endif

void vibrancer(unsigned char *pixel) {
    int r = pixel[0],
        g = pixel[1],
        b = pixel[2];

    // TODO remove unnecessary calculations
    int min_rgb = min3(r, g, b);
    int max_rgb = max3(r, g, b);
    int sum = r + g + b;

    int m;

    if (LUMINANCE_METHOD == 3) // twist
        m = 3*sum - 4*(min_rgb + max_rgb);
    else if (LUMINANCE_METHOD == 2) // nomax 
        m = (sum - max_rgb) / 2;
    else if (LUMINANCE_METHOD == 1) // nomin
        m = (sum - min_rgb) / 2;
    else // simple
        m = sum / 3;

    r -= (m - r) / VIBRANCE_STRENGTH;
    g -= (m - g) / VIBRANCE_STRENGTH;
    b -= (m - b) / VIBRANCE_STRENGTH;
    
    pixel[0] = clamp(r, 0, 255);
    pixel[1] = clamp(g, 0, 255);
    pixel[2] = clamp(b, 0, 255);
}

int main(int argc, char **argv) {
    if (VIBRANCE_STRENGTH == 0) {
        printf("VIBRANCE_STRENGTH cannot be zero");
        return 1;
    }

    char* input = argv[1];
    char* output = argv[2];

    if (argc < 3) {
        printf("Please specify input and output files\n");
        return 2;
    }

    int width, height, channels;

    unsigned char *img = stbi_load(input, &width, &height, &channels, 0);

    //printf("Width: %d, Height: %d, Channels: %d\n", width, height, channels);

    if (img == NULL) {
        printf("Error loading image\n");
        printf("%s\n", stbi_failure_reason());
        return 1;
    }

    if (channels < 3) {
        printf("Not enough channels (%d)", channels);
        return 1;
    }    

    for (int y=0; y<height; y++) {
        for (int x=0; x<width; x++) {
            unsigned char *pixel = img + (y * width + x) * channels;

            vibrancer(pixel);
        }
    }

    stbi_write_png(output, width, height, channels, img, width * channels);

    return 0;
}