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As I've been developing a few images into tone mapped images in Photomatix, some of the skies that were blue seem to be turning purple. I'm not quite sure why. I take 3 bracketed RAW images, which individually all seem to have blue skies. When combined and tone mapped in Photomatix, the skies turn quite purple to my eye. I haven't altered the temperature or gamma in Photomatix at all.

Non-tone-mapped, untouched, image on the left, Tone-mapped from 3 source RAW files, no processing done outside of Photomatix on the right: enter image description here

Photomatix settings:

enter image description here

Second example, single file on left, tone-mapped image on right: enter image description here

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Shooting a standard color chart (available in small and large sizes) would give a better idea of your light conditions. To me, both look not quite right. But my monitor is not calibrated. –  Skaperen Feb 12 '13 at 3:45

2 Answers 2

The interesting thing here is that's not a colour cast, the hue values are messed up. It's not just that all the colours have been pushed toward purple, which can happen for certain white balance settings, what's actually happened is that all colours are shifted round the colour wheel, blue/cyan -> purple, orange/brown -> green.

Here's the right hand part of the first image, with the hue shifted left 16 degrees:

When compared the left hand side the colours are not exactly right but pretty close:

This to me indicates that there's nothing you've done wrong this is a bug in Photomatix. Either the internal representation uses a YUV style colour space and is suffering from some sort of offset error, or your camera has somewhat nonstandard dyes in the CFA and Photomatix is using the wrong camera profile when demosaicing the RAW images resulting in the colours being shifted as the blue values are interpreted incorrectly.

My money is on the second explanation as I've seen very similar results when doing RAW conversions in Lightroom if you modify the hue of the blue primary in the camera profile.

An easy way to check this hypothesis is to convert your images to 16bit TIFFs and then import them into Photomatix. If it turns out this is the case there may be some settings in Photomatix to do with RAW conversion. If not you may have to file a bug report. In the meantime you should be able to shift your colours back using the Hue/Saturation/Lightness dialog in Photoshop/GIMP.

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+1 great spot there Matt! –  Nick Miners Feb 12 '13 at 9:53
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I use Photomatix a lot and have never seen this. I do my RAW processing in Lightroom, not in Photomatix. Try processing the RAWs outside photomatix and get back to us. Interesting... –  Paul Cezanne Feb 12 '13 at 11:57
    
So I took the 3 raw files and converted to TIFF-16bit in PS, and pushed those into Photomatix. The results are certainly different, even with the same exact settings in Photomatix. I tried both AdobeRGB and sRGB with similar results. Take a look, the purple is gone but contrast seems to have suffered(trees,bark,etc.) - i.imgur.com/zfr4Bk2.jpg I think you nailed it that this is a bug in Photomatix for my DSLR(Canon 6D). But using it with TIFF seems to introduce other issues for me. –  dpollitt Feb 13 '13 at 4:04

Blues turn purple when the saturation of the blue is reduced in LAB because LAB is not perceptually uniform. See http://www.brucelindbloom.com/index.html?MunsellCalcHelp.html

In your first picture, the sky is already very saturated in the "before" version. I also saw that you have the saturation setting pumped up. I have no idea what color space Photomatix uses, but try reducing the saturation- it could be that the image is saturated beyond the gamut of your monitor.

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