Designed to take a 1024x512 texture split into 4 equal parts. To do this just use the cropping function of your
image editing program to reduce the top left section to 512x256, then the top right section etc.

Depending on the size of the original picture, better results may be achieved by reproducing the last column of
pixels from the left hand images and adding them to the first column of pixels in the right hand images.