how come people assume there are only Little Endian machines. This mmap-technique wouldn't work on Big Endian like this, this is inaccetable!

However, you can still mmap and properly call ntohs() on each color channel value (if you access it). These functions won't hurt performance too much anyway, if at all. If you show me a measurable difference between using LE and BE, I owe you a beer, okay? :)