Sunday, July 15, 2012

Car Show and the Day Linux Failed Me!


First a quick word about the Atlantic Nationals Car Show in Moncton. Naturally I took a lot of pictures. Have a look. There were some amazing works of art on wheels this year!

However, I had a devil of a time processing these files this time. See those weird Magenta artefacts in the picture above? I had noticed this happening with my Port Elgin show pictures, but somehow managed to work around most of the really bad ones. But part way through processing my RAW files of the Moncton event using RawTherapee in Linux, I was ready for another kind of therapy! The only way I could really get rid of all the Magenta was to convert the pics to B&W, and it left me wondering if my awesome new 7D might be defective. I tried opening my files with other Linux tools - UFRAW and DarkTable, and got exactly the same results. So I went to bed, feeling rather sad, and the next morning, I thought I would try Canon Digital Photo Pro (DPP) under Windows-7. Success! The files all looked awesome and there was no strange colour artefacts of any kind. So, I worked through all the pictures again using DPP.

Next step was to try to determine where the trouble really was happening. I installed RawTherapee in Windows (yep - there is a Windows version), and to my mix of dismay and relief, I found that opening my RAW files in the Windows version of RawTherapee gave exactly the same artefacts as the Linux version! So, I went online and joined RawTherapee Forums to see if anyone else was having the same problems, and it turns out that several people were reporting this same bug. And, two of the complainants reported they were using the EOS 7D camera; the others didn't mention what kind of camera they were using.

It turns out that most, if not all RAW Software developed under Linux all use a more fundamental Command Line software called DCRaw as a base. I didn't find a definitive answer on RawTherapee Forums, but I'm guessing that, although the EOS 7D is one of the supported cameras, it could be that the interface between this camera and the DCRaw software needs some further work. That's why I was seeing the same weird Magenta streaks in UFRaw and DarkTable also, I'm guessing.

So, a Linux Program let me down. I'm going to submit a bug report of my own, stating my suspicions. Meanwhile, I can live with using the Canon DPP Software in Windows-7. Actually, having tried it, I found it to be very pleasant to use - the various adjustments were exactly like the basic settings on all Canon DSLR models themselves, with a lot of additional functionality as any good RAW file developer should have. Thumbs up to Canon DPP!

Update - I gave my latest files a try with Photivo, which is the most comprehensive Open Source RAW Developer of all, and found the same problem existed. I had never seen this before when using my former camera, the EOS 40D (I even re-opened some old files taken with that one, just to be certain). It turns out that Photivo also is based on DCRaw. It enabled me to reduce the Magenta however, because it allows certain adjustments on the Camera Input, which is defaulted to the Adobe Colour Profile. When I selected "Flat Profile", or "External Profile", the nasty Magenta does reduce quite a bit, but not completely. I think I have my case prepared for a Bug Report - I'll keep you all posted.

Further Update - the sun came out today and I set out to take some deliberately bright pictures with my camera set on regular RAW. My suspicions were verified - where there were bright highlights, this time there was no magenta cast at all, proving (I think) that DCRaw isn't set up to deal with Canon's MRAW and SRAW file algorithms.

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