Load a PNG image directly.
SDL_Surface * IMG_LoadPNG_RW(SDL_RWops *src);
an SDL_RWops to load image data from.
Returns SDL surface, or NULL on error
If you know you definitely have a PNG image, you can call this function, which will skip SDL_image's file format detection routines. Generally it's better to use the abstract interfaces; also, there is only an SDL_RWops interface available here.
This function is available since SDL_image 2.0.0.