CornerFix 1.1.0.1

CornerFix 1.1.0.1 is yet another extremely useful utility for everyone. It actually corrects for color dependent vignetting in digital images. All digital cameras are some extent subject to this; current generation sensors are highly IR sensitive, so there needs to be a IR filter somewhere. But the combination of sensors and IR filters also cuts into the red part of the spectrum, and do so in a way that depends on the angle through which the light bends as it travels to the sensor. So red gets cut more in the corners. Most DSLR's do this a bit - take a picture of a white wall and you will probably see it, although many cameras correct internally to a greater or lesser extent.

Leica's M8 has a particular problem in this regard. Historically, one of the advantages that rangefinder cameras had was that the back of a rangefinder lens can be a lot closer to the film surface than is the case for a film SLR - the SLR needs space for the mirror, which a rangefinder doesn't have. So in the film world, rangefinder lenses had a lot more design freedom that SLR lenses - wide-angle lenses that on a SLR had to be reverse telephoto designs could be normal designs on a rangefinder.

M8's can correct for this problem themselves, but there are two issues for users - firstly, your lenses must be coded, which means that it must be a Leica lens, either new enough to have been coded when it was manufactured, or one that has been sent to the factory to be upgraded. So anyone with a non-Leica lens or one that can't be upgraded is out of luck, unless they somehow code the lens themselves. The second problem is that the M8's correction is "one size fits all"; it's designed for average situations, and sometimes doesn't do well in unusual lighting.

CornerFix allows the cyan corners problem to be corrected for any lens, in more or less any lighting situation, by post processing the camera's image file. The right hand side of the main window in the screen shot shows the corrected image. CornerFix is available for the Mac and for Windows. It's free and open source, released under the GPL. Note however that image must be a DNG formatted file - CornerFix doesn't work with TIFF or JPEG files.

Enhancements: Jul 15 2009

• Devignetting application for Leica M8 digital cameras;
• Fixed the "cyan corners" problem when using wide lens with IR filters and decodes data in the M8's MakerNotes