Detect if a PNG has a palette and load palette+data with libpng

paletted_png.c

// This examples read a PNG and its palette

#include <png.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>

int main() {
    png_image img;
    png_bytep img_data;

    memset(&img, 0, sizeof(png_image));
    img.version = PNG_IMAGE_VERSION;

    if (!png_image_begin_read_from_file(&img, "png.png")) {
        puts("Error reading PNG");
    }

    // This can be used to check if the PNG has a palette
    printf("%d\n", img.format & PNG_FORMAT_FLAG_COLORMAP);

    // If so we can read it
    img.format = PNG_FORMAT_RGBA_COLORMAP;

    printf("%d\n", PNG_IMAGE_COLORMAP_SIZE(img));

    // To here
    png_bytep colormap = malloc(PNG_IMAGE_COLORMAP_SIZE(img));
    img_data = malloc(sizeof(uint8_t)*PNG_IMAGE_SIZE(img));

    if (png_image_finish_read(&img, NULL, img_data, 0, colormap) == 0) {
        puts("Error reading PNG");
    }

    // Palette (first entry)
    printf("%d %d %d %d\n", colormap[0], colormap[1], colormap[2], colormap[3]);
    // Image (first pixel)
    printf("%d\n", img_data[0]);

    free(colormap);
    free(img_data);
    png_image_free(&img);

    return 0;
}