Properties of a Center/surround Retinex Part Two: Surround Design

The last version of Edwin Land's retinex model for human vision's lightness and color constancy has been implemented. Previous research has established the mathematical foundations of Land's retinex but has not examined speciic design issues and their eeects on the properties of the retinex operation. We have sought to deene a practical implementation of the retinex without particular concern for its validity as a model for human lightness and color perception. Here we describe issues involved in designing the surround function. We nd that there is a trade-oo between rendition and dynamic range compression that is governed by the surround space constant. Various functional forms for the retinex surround are evaluated and a Gaussian form found to perform better than the inverse square suggested by Land. Preliminary testing led to the design of a Gaussian surround with a space constant of 80 pixels as a reasonable compromise between dynamic range compression and rendition.