static int pixel_size(enum img_fmt fmt);
static size_t def_read(void *buf, size_t bytes, void *uptr);
static size_t def_write(void *buf, size_t bytes, void *uptr);
static int pixel_size(enum img_fmt fmt);
static size_t def_read(void *buf, size_t bytes, void *uptr);
static size_t def_write(void *buf, size_t bytes, void *uptr);