[Play Raw] Tree leaves under a "very nasty" blue LED lighting

Just got my brand new d610, wanted to play around in harsh conditions last night.
Little did I know that this blue LED lighting from underneath would completely confuse Darktable 3.0.2 and burn the blues out of the picture.

20200515_0052.NEF (29.5 MB)

I’m told it’s a gammut mapping problem actually being worked on here: https://github.com/darktable-org/darktable/pull/4940

Here is basically what I get by default on Darktable 3.0.2:

For some reason, switching the input color profile to adobe RGB hacked around the problem and “sort of” got me my colors back, but I had to tweak exposure and the shadows as I definitely lost some hue (is that the right word?)

The picture is not that interesting, but it might be useful to validate future fixes to this situation and see if they maintain color sanity even with this corner case picture :slight_smile:

Interestingly, the effects are less severe on darktable 2.6!

I’m actually curious of what the easiest process to “repair” the colors might looks like, until the gamut mapping is “fixed” or improved.
A friend of mine “opened the picture on his mac and saved it” (that’s all I know about the process), and this is what he got:

As far as I know this is exactly how it should look like initially, so if you take the challenge, you can consider this the goal post :wink:

PS: On a last note, I actually do like the second one best, as it has darker blacks and accidentally cleaned some parts of the background to emphacize the leaves, although the last one is the most faithful one, at least as a starting point.

This file is licensed Creative Commons, By-Attribution, Share-Alike.


Welcome @koolfy! Interesting experiment.

20200515_0052.NEF.xmp (9.6 KB)

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20200515_0052.NEF.xmp (22.5 KB)

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@koolfy Neat! Welcome to the forum and thanks for sharing! People like @ggbutcher would have a blast with it.

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I imported a bayer patterned unprocessed raw file into GIMP ignoring all proper colour processing. I demosaiced by resizing it to 50%, white balanced it with levels by eye, and applied a curve to a duplicate layer image to brighten it. The original layer was on top and set to ‘HSL Color’.

I also added some local contrast special sauce.

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I’m guessing darktable doesn’t have a built in profile for this camera? It’s using a simple color matrix embedded in the raw file that doesn’t resolve well in extreme colors. You can see this problem in rawtherapee more clearly, and also fix it using Adobe’s profiles. I don’t think darktable has added this feature yet which is one of the reasons why I stopped using it for now

20200515_0052.jpg.out.pp3 (12.0 KB)

Anyway if you fiddle around with highlight recovery or look at the clipped region you will realize there is also the phenomenon of simple raw clipping, which makes this a double problem.

Blue LEDs are evil…

nasty.blue.led.nikon.d610.nef.xmp (9.4 KB) darktable 3.0.2

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I did a process of this image last night with a SSF profile from my Nikon D7000, and got similar results:

I’m working on the post to describe how one can make their own SSF profiles from simple ingredients found in your kitchen… :smile: Well, almost… should be posted soon.


I tried to match your reference image with RawTherapee.

20200515_0052.NEF.pp3 (12.1 KB)

There is a very good thread on blue LEDs and out of gammut if you haven’t already seen it:

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20200515_0052.pfi (36.8 KB)

A greener version :frog:

20200515_0052.NEF.xmp (5.4 KB)