RAW Colour cast problem

Gewitty

Senior Member
Having recently upgraded to the D7200, I originally shot a lot of stuff in JPG with no difficulty. However, I'm now switching to RAW (NEF) and have encountered an odd problem. Whenever I download pictures into RAW processing software the images have a very pronounced magenta colour cast. I can get rid of this with some work, but it shouldn't be there, so I'm wondering what causes it.

I should say that I don't use Windows, having opted (wisely :playful:) to abandon it about eight years ago in favour of Open Souce software. I currently run Linux Mint 17.3 as the OS, with my workflow handled by DigiKam (image processing and cataloguing, similar to Lightroom) and GIMP (an excellent Open Source alternative to Photoshop). In addition to these main applications, I also have a couple of alternative RAW processing programs, but the colour cast problem appears in all of them.

I have raised this issue with several of the pro's in my camera club, but they are as mystified as I am about what causes this. If anyone has any experience of such a problem, I'd be grateful for any advice on how to fix it.
 

Danno

Senior Member
First of all, Welcome to the forum. I have a D7200 and shoot in RAW and I have to say that I do not have an issue, but I will say there are a lot of folks here that will be willing to help. The first thing needed will be some example photos with the exif data. Here is a link with instructions. It is important that you stay at 1000 pxls on the long side to retain the exif data. http://nikonites.com/new-member-int...st-images-inside-your-post.html#axzz45837ujXG
 

Gewitty

Senior Member
Thanks for the fast reply Danno. I've attached a JPG version which is a straight export from the original RAW file, just resized.

test_shot.jpeg

EXIF Data is embedded.
 

Danno

Senior Member
Like Mike I am curious about the white balance, but I see that this is at 8000 ISO and I have seen some strange color noise at high ISO when I have plaid with it that high that could be causing the problem. I like to stay below 3200.
 

Gewitty

Senior Member
Yes. I've been shooting in full manual, with Auto ISO which does tend to go high quite often. I'll try a few shots using a lower manual ISO setting.
 

Gewitty

Senior Member
That certainly gets the colour balance right in the JPG, which I can do with the original RAW file after some fiddling. Maybe the colour cast is just a natural effect in the RAW files that I'll have to live with.
 

Horoscope Fish

Senior Member
I'm curious what lens you were using to take these shots because on top of the magenta color-cast I'm also seeing what appears to be a staggering amount of green chromatic aberration in both the original, and mikew's corrected version (look in the upper left corner where the branches meet the sky).

To rule out a problem with your software causing this issue, I'd like to get a copy of the original raw file to see how it looks when opened in Photoshop or Lightroom. Can GIMP can open your D7200 raw files natively? I don't really think GIMP would cause this, but I do think it's something that needs to be ruled out.

If this does turn out to be a WB issue, it may be possible to permanently correct it in-camera using the menus. I adjusted the Auto-WB setting on my D750 to be slightly warmer because Nikon bodies, generally speaking, shoot a little on the cool side. We can do the same, I believe, on your D7200 and reduce the magenta.
 

mikew_RIP

Senior Member
Looking at the original i wonder if the color temperature was thrown off by the light reflecting off the dead leafs,are other images displaying this error.
 

Gewitty

Senior Member
To answer the various questions in the recent replies:

The lens I'm using is a Sigma 18-200 f/3.5-6.3 DC Macro OS HSM. I don't think this is relevant, but I did have a problem with front-focusing on this lens and had to push the auto-focus adjustment on the camera almost to its maximum in order to get it sharp

The D7200 is a Nikon refurb body

As far as I understand, adjusting the WB settings in the camera would have no effect, as RAW ignores WB, leaving adjustments to the post processing software

I don't think the problem was caused by any light reflections, as the same colour cast appears to varying degrees in all RAW files

I have uploaded a copy of the original NEF file (39.2Mb) to my DropBox public folder, which can be accessed here: https://db.tt/Mek8Vm53
 

WayneF

Senior Member
Maybe the colour cast is just a natural effect in the RAW files that I'll have to live with.

The effect is that there is no white balance correction in raw files. Raw is raw. Meaning, other than exposure, there are no camera settings applied to raw data. It is not even RGB yet. The huge advantage of raw is that we can correct white balance later, after we can actually see it, and can know and judge what we are doing, with better tools.

I know very little about Gimp, I think it is good, but I know it is NOT a raw editor. I "think" that UFRaw is the plan there, to correct the raw images first. Then, the raw editor MUST output a new JPG or TIF with the corrections applied, for Gimp to see then.

But the main idea of raw is that we correct white balance later, ourself, leisurely at home. Also settings like camera color profile (like Vivid or Landscape) are not in raw either, but can be appled later, after we can see what we are doing. And we can tweak exposure too. But the raw plan is that we see it and apply these settings ourself.
 
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Gewitty

Senior Member
Thanks Wayne. That is my understanding of the way RAW files are handled.

GIMP does not natively handle RAW files, but there is a plugin for UFRaw which works well. That said, I do most of my RAW processing in either RawTherapee or DigiKam, RawTherapee being the most extensive program. It's the fact that the colour cast shows up in any of these programs which makes me question if this is normal, or a possible problem with the camera. It's clearly not the lens, because JPG's appear perfectly.
 

Horoscope Fish

Senior Member
The lens I'm using is a Sigma 18-200 f/3.5-6.3 DC Macro OS HSM. I don't think this is relevant, but I did have a problem with front-focusing on this lens and had to push the auto-focus adjustment on the camera almost to its maximum in order to get it sharp...
I don't think it's relevant either, really, but I was curious. I'm still shocked at the amount of green CA you have going on...


I have uploaded a copy of the original NEF file (39.2Mb) to my DropBox public folder, which can be accessed here: https://db.tt/Mek8Vm53
Perfect... Downloading it now. I just want to see how this looks in PS.

Edit: Okay, my outdated version of PS here at the office won't open your D7200 .NEF but another image editor I use, IRFanview, will. And when I open your RAW file in IRFanview it looks like this (no corrections done to your raw file other than reszing to 1,000 pixels on the long edge and a "Save-as JPG" for posting here):
...
....

DSC_1131.jpg
 
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Gewitty

Senior Member
That looks pretty good for an unprocessed file to me, which makes me wonder what might be happening in my own PC, given that at least three RAW processing apps show the colour cast, whilst yours doesn't.

Do you see the same amount of CA in the RAW image?
 

Horoscope Fish

Senior Member
That looks pretty good for an unprocessed file to me, which makes me wonder what might be happening in my own PC, given that at least three RAW processing apps show the colour cast, whilst yours doesn't.
It's very curious indeed. If you want to check it out yourself, IRFanview is a free download but you'll need to install the optional "plug-ins" to be able to handle raw files. It's a really handy little app to have on hand.


Do you see the same amount of CA in the RAW image?
I do not. Your raw file looks very, very good in IRFanview.

When I open the resulting JPG in Photoshop, I'd say the image needs nothing more than the standard sort of processing any raw file would need.
 
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