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Author Topic: DXO - DNG blown highlights  (Read 5023 times)
patrickmercier
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« on: April 16, 2010, 09:24:21 PM »
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I really like the DXO software for its lens correction and lens softness features.  However, for image touch-ups and fooling around with colors/exposures, I find the interface clunky and I much prefer Lightroom.  Thus, my work flow goes something like this: DXO 6.1.2 (auto corrections) -> DNG file -> import into Lightroom -> touch up -> export JPEG.  For the most part, this works fine.  However, I am finding specific situations where some goes very wrong.  Consider the following image and its 100% crop (the picture will not be winning any awards BTW, but it serves the purpose of my illustration):

[attachment=21540:DSC_0551_DXO.jpg]
[attachment=21543:DSC_0551_DXO_crop.jpg]

This is an image taken with my Nikon D90, processed in DXO with NO corrections applied, and output as a JPEG.  At the same time, I've also output a DNG file and imported it into Lightroom (I've tried 2.5 and 3.0 Beta 2).  All settings in lightroom are left at default (e.g. no white balance, etc..).  When I look at the files in lightroom (or export as JPEGs), I see this weird green areas in locations where there are some blown highlights.  Full picture and 100% crop below:

[attachment=21541:DSC_0551_DXO_LR.jpg]
[attachment=21542:DSC_0551..._LR_crop.jpg]

Note that this doesn't happen when processing the original NEF file directly in LR, bypassing DXO completely.  Note that the DNG file output from DXO also looks this way when viewed with the picasa photo viewer.   Also, these green blown out areas do not appear anywhere in DXO.  Finally, it doesn't matter what settings I apply in DXO, I see similar greens areas in the DNG files in any program other than DXO.  

So my best guess (and I'm not an expert in this area) is that when DXO de-mosaics the DNG, some highlight are completely blown out (and thus appear as white, as they should), but some of the highlights are only blown out in certain colors.  In other words, green is not blown out for whatever reason, and remains in the image.  

Does this seem like a reasonable explanation?  Has any one else had any experience with this?  Any suggestions as to how to solve this?  I'd really like to keep my work flow similar, as I like the auto features in DXO, but really prefer LR for everything else.  I've noticed this effect in some other less-extreme-lighting pictures before, but until now just thought it was part of the actual lighting, not a figment of the DXO DNG conversion.

Thanks in advance for anyone's help!
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madmanchan
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« Reply #1 on: April 16, 2010, 10:50:54 PM »
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Hmm, I'm stumped on this one. Out of curiosity, what happens when you try to export the same image from DxO as a TIFF or JPEG (instead of as a DNG)? Do you also see the strange green areas?
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patrickmercier
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« Reply #2 on: April 16, 2010, 11:10:01 PM »
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No, there's no strange green areas when I export a JPEG from DxO (actually, that's what the first two images are in my original post - DxO outputting a JPEG directly).  I also tried TIFF and it was ok.  The problem seems to be only in the DNG files when read by another program such as LR.
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madmanchan
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« Reply #3 on: April 17, 2010, 05:34:51 PM »
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Can you post an example DNG file that was created by DxO?
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patrickmercier
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« Reply #4 on: April 17, 2010, 06:23:46 PM »
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Sure, of course!  The file is fairly big (28MB), so I couldn't attach it here.  Instead, I uploaded it to rapidshare:

http://rapidshare.com/files/377097044/DSC_0551_DXO.dng

Let me know if this doesn't work for anyone and I can try a different upload service.
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madmanchan
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« Reply #5 on: April 18, 2010, 06:29:49 AM »
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Thanks, that link did work for me.

It looks like the strong green areas are "baked into" the DNG image data. (The DNG image is basically a TIFF at this point, in terms of format, so it's just like any other image.)

This appears to be an issue with how DxO is creating the image data when writing out a DNG. I suggest following up with them and submitting to them this example file.
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patrickmercier
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« Reply #6 on: April 27, 2010, 11:14:16 AM »
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Just a follow up here: I took your suggestion and passed the data along to DxO.  The first person I discussed this with wasn't sure what was going on, and he was going to forward it to engineering.  They are very busy at the moment on other projects, but I was assured someone would get back to me eventually.

For now, I am cutting DxO out of my workflow.  I'm realizing that the linear DNG files that DxO outputs are not nearly as robust as my D90's NEF files (even without the aforementioned problem).  For instance, once highlights are blown in DxO, there's no way to recover then in LR (though it may be possible to recover them in LR with the original NEF file).  Also, I've noticed I have less white balance room to work with using the DNGs in LR instead of the NEFs in LR.  

I think that until DxO can output better raw files, I will probably stop using it, which is a shame.  I really enjoy the hands-off CA, distortion, and vignetting corrections DxO offers.
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FranciscoDisilvestro
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« Reply #7 on: April 27, 2010, 03:07:32 PM »
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The linear DNG files that DXO produces have some processing (demosaicing, interpolation), which according to the DXO team are necessary steps before applying the lens corrections.

An important issue is that it clips highlights (as you mention), compared to the original RAW files. I don't know if it is a limitation of the process or something that can be corrected in the program. A possible workaround is to perform highlight recovery or exposure compensation in  DXO (like if you were producing a tiff file) to make sure there are not clipped highlights.

Even if the linear DNG files from DXO are not exactly RAW files as the NEFs, they are not color space encoded, and you can still apply a camera profile in LR or ACR and correct WB using color temperature. I haven't tested if they have less room to correct WB than the NEFs, but I wouldn't be surprised about that.
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