1. A method of processing an RGB format image comprising: traversing each pixel of the image in a single pass over the image; applying an inverting function to a combination of each color plane value for a pixel; applying a recursive filter to each inverted pixel value, said filter having parameters which are derived from previously traversed pixel values of said image; and combining said pixel value with said filter parameter for said pixel to provide a pixel value for a processed image wherein said recursive filter parameters H(i,j) comprise: 
 H ( i,j )=α H ( i,j− 1)+(1−α) ( f ( G ( i,j,k ))) where: α comprises the pole of the filter; G(i,j,k) comprises the pixel value for the respective red (R), green (G) or blue (B) color plane k; and f(G(i,j,k)) comprises said inverting function.