Use of GIMP Retinex filter to enhance the visibility of craquelure: example n. 6

<p>In the previously proposed figures (*), the GIMP Retinex filter had been applied to greyscale images, to enhance the visibility of dark craquelure in bright backgrounds. After processing, a black and white map had been obtained, suitable for any possible further processing, even for automatic processing. In (**), we have shown an example of the use of GIMP Retinex to observe the craquelure in dark areas. We observed that when craquelure is present in bright and dark scenes, it seems better to use the GIMP Retinex directly on the colour image. Here an example is given on the Lady Seated at a Virginal, a painting created by Dutch artist Johannes Vermeer&nbsp; (highest resolution), courtesy Wikipedia.&nbsp; A is a detail. A0, A1,A2, A3, and A4 are the images we can obtain by applying GIMP Retinex filter on A, level=low, scale=250, scale div.=8, with dynamics equal to 0,0 1,0 2,0 3,0 and 4,0 respectively. On this detail, it seems that the best manner to enhance the visibility of craquelure is that of using dynamics 2,0. In the lower panel, a larger detail of the painting is given, processed by the filter with dynamics 2,0. The example suggests that use of Retinex filtering on colour images represents a fast manner for enhancing in them the visibility of craquelure.</p> <p>(*) Figures at http://doi.org/10.5281/zenodo.3956124 http://doi.org/10.5281/zenodo.3956204 http://doi.org/10.5281/zenodo.3957439 http://doi.org/10.5281/zenodo.3957799<br> (**) http://doi.org/10.5281/zenodo.3959017</p>