Unifying Path and Center-surround Retinex Algorithms

Retinex is a theory of colour vision, and it is also a well known image enhancement algorithm. The Retinex algorithms reported in the literature are often called path-based or centre surround. In the path-based approach, an image is processed by calculating (reintegrating along) paths in proximate image regions and averaging amongst the paths. Centre-surround algorithms convolve an image (in log units) with a large-scale centre surround-type operator. Both types of Retinex algorithms map a high dynamic range image to a lower-range counterpart suitable for display, and both are proposed as a method to simultaneously enhance an image for preference. In this paper, we reformulate one of the most common variants of the path-based approach and show that it can be recast as a centre-surround algorithm at multiple scales. Significantly, our new method processes images more quickly and is potentially biologically plausible. To the extent that Retinex produces pleasing images, it produces equivalent outputs. Experiments validate our method.