// gcc <file>.c -lpng; ./a.out < VhGrd.png > out.png

#include <stdlib.h> // malloc, EXIT_*
#include <string.h> // memset
#include <png.h>

#define EXIT_PNG(F) if (!F) { \
    fprintf(stderr, "%s\n", img.message); \
    return EXIT_FAILURE; \
}

int main(int argc, char **args)
{
    png_image img;
    memset(&img, 0, sizeof(img));
    img.version = PNG_IMAGE_VERSION;
    EXIT_PNG(png_image_begin_read_from_stdio(&img, stdin))

    void *pixels = malloc(img.width * img.height * 4);
    EXIT_PNG(png_image_finish_read(&img, NULL, pixels, 0, NULL))

    EXIT_PNG(png_image_write_to_stdio(&img, stdout, 0, pixels, 0, NULL));
    return EXIT_SUCCESS;
}