#include <png.h>
void png_set_gAMA(png_structp png_ptr, png_infop info_ptr, double file_gamma);
void png_set_gAMA
Sets the gamma value of an image to "file_gamma" and sets gAMA chunk information to valid for the image.
png_set_gAMA() shall generate warning if file_gamma > 21474.83 or file_gamma = 0