Combining White Patch Retinex and the Gray World Assumption

5 Combining White Patch Retinex and the Gray World Assumption 

Another possibility is to subtract space average color in order to adjust the colors of the image (Ebner 2003a). This method of color constancy was also used by Moore et al. (1991). 

Note that this transformation does not necessarily move the average to 0.5. If the pixel values are nonlinear, then the average of the transformed values may be different from 0.5. 

The shift and rescale method was implemented in parallel as follows. Local space average color was calculated on a grid of processing elements as described in the preceding text. Let 

As the maximum deviation is passed from element to element, it is multiplied by (1 — pj). Therefore, over time, the value dj (x, y) will reduce to zero. The factor pd determines how soon this reduction will occur. 

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