Use of GIMP Retinex filter to enhance the visibility of craquelure: example n. 3

<p>In the image, A represents the original image. It is a detail of the Gioconda, by Leonardo da Vinci, (highest resolution), courtesy Wikipedia.&nbsp; B is the grey-tone corresponding image. C is the image that we can obtain using the GIMP thresholding (threshold tone T = 127), applied to B. D is the image that we can have, applying GIMP Retinex filter on B (level=low, scale=250, scale div.=8, dynamics=4,0). E is the result of applying Retinex once more (the same parameters used to obtain D) on D. The iteration continues obtaining E from D, and F from E, using the same parameters. G, H and I are the result of thresholding of the D, E and F images respectively (T = 127). The example shows that the use of a thresholding on a Retinex filtered image gives much better results than the simple thresholding. The iteration of the Retinex filter is able of enhance the visibility of the craquelure in the dark areas. This approach, that is the use of Retinex filtering, represents a fast manner for enhancing the visibility of craquelure. Other examples are given at http://doi.org/10.5281/zenodo.3956124 and http://doi.org/10.5281/zenodo.3956204</p>