Monthly Archives: February 2016

New Zealand, Photography

Technical Epilogue: Very Simple Method for Enhancing Saturation and Contrast

Introducing CSI

I have recently been revising the photo processing business in the hope of coming to terms with all of the photos from the last visit, perhaps even in time for a new trip. New life appears to have been breathed into PHP’s Imagick project so that it will now do a number of things that haven’t yet even appeared in the official documentation, although, if you scratch beneath the surface they are there. This means that my photo processing stuff can be developed with Imagick, which is preferable from a programming point of view (repeat after me: (I (do (not (like (lisp…)))))). After sorting out the median pixel business I was finding out how to get Imagick to do GIMP “grain extract” layering when I made an interesting discovery. Read more…

Photography

Technical Epilogue: On the Purple Fringe

A problem that arises in high contrast photography is purple fringing due to short wavelength light being refracted around a dark/bright transition. This is different from chromatic aberration of the lens which results in green/purple fringing at such transitions. The latter can be largely removed by resizing the red and blue channels. The classical fix for pure purple fringing has been to use Darla’s Purple Fringe script for the GIMP, but the results are rather modest and require fiddling with afterwards, as shown in these two images:

Lake Waikaremoana
Fig. 1: Lake Waikaremoana, March 20, high contrast snapshot with substantial purple fringing
Waikaremoana Darla PF
Fig. 2: Purple Fringe reduction with Darla’s Purple Fringe for GIMP. Note residual fringing

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