Creating generic camera input profile
23 October 2016
Lately I tend to spend considerable amount of time trying to get the colours in my photos accurate. It is not unusual that I revisit my white balance temperature and green tint settings multiple times over a few days, until I am satisfied with the result.
Few months back I came across a video describing how to create a camera input profile with ColorChecker Passport Photo target, Darktable, and Argyll CMS. It seemed to have a potential to give me a better starting point for my photo processing. I have written my take on the topic in another article.
That video started my quest for a better camera input profile and learning more about colour management in general. Somewhere along the way I came across website of Elle Stone with lots of useful information. Some of her articles deal specifically with camera input profiles. I would like to share my experience with them, in case someone finds it useful.
Generic camera input profile
One of the email lists to ask questions about camera profiling is Argyll CMS list. However don't expect that people responding on the forum all agree on the answers. There seem to be a variety of opinions on topics like camera profiling.
But now, let's look at Elle's articles:
The information provided is very detailed and worth a careful study. There is a lot to learn from them. After trying out most of what Elle describes, here is my experience:
I purchased Wolf Faust's IT8.7 target (Order# C1). Even though I made a light trap and a Teflon tape white patch as per description in the first article, they didn't seem to work that well for me. After many experiments I think my light trap is not giving me black enough black and my white Teflon patch is not an ideal white either. My suggestion is not to bother with them. Photograph the target itself and then follow Elle's step by step procedure.
I spent some time reproducing Elle's procedure in Darktable. She describes her procedure using RawTherapee and her own patched version of Gimp 2.9. While RawTherapee is readily available, one might need to spend some time compiling Elle's Gimp-CCE. This might be a worthwhile effort. But if you don't need it for anything else, try my procedure using Darktable only instead. My procedure is described for another target. But if you read and understand Elle's instructions, you will be able to combine these two easily.
I created two profiles for my Nikon D7100 with the IT8 target so far. One on an overcast afternoon (colour temperarute circa 6200K as measured with ColorMunki Display ambient light function and DisplayCAL) and one with the light that Elle describes as close enough to D50, i.e. on a sunny day with Sun at 45 degrees above horizon (altitude). To find suitable time I used online Sun calculator (they have an Android version too). You can download my profiles below if you wish.
I experimented with measuring ambient light colour temperature with ColorMunki Display and DisplayCAL as mentioned above. On a cloudy day it worked fine. However on a sunny day I was getting error message that the light is too bright. I tried to cut down the amount of light with a variable neutral density filter placed on top of the ambient light difuser (Marumi ND2-400 variable). This worked to an extent - I was getting plausible readings. But I noticed that those readings varied for each setting on the variable filter - perhaps the filter wasn't neutral enough and was introducing a colour cast. The darker the setting the stronger the colour cast.
Warning: As far as I know, the instrument is not intended for measuring direct sunlight. It is possible that you could damage it by trying to do so.
When I was procesing my shot taken on a cloudy day with colour temperature 6200K, I thought I need to use target reference file for that temperature as well as add syntetic white patch of the same temperature later on in the process. Elle corrected me that this is not the right way to do it. One should use the default D50 target reference file and D50 syntetic white patch, regardless of colour temperature of the light when target shot was taken.
Profiles for Nikon D7100
All target shots were taken with Nikon 50mm f/1.8 lens stopped down to f/7.1 (see Diffraction Limited Aperture Estimator) and Wolf Faust's IT8.7 target C1. Profiles were produced using my adapted procedure with Darktable and Argyll CMS.
|Light Conditions||ICC Profile|
|Clear and sunny day. Sun at altitude 45 degrees. Approximately 5000K.||Download|
|Overcast afternoon. Sun at altitude about 30 degrees. Approximately 6200K.||Download|
Please let me know if you notice any issue or inaccuracy in this article.
Article Creating generic camera input profile by Tomas Sobek is licensed under a Creative Commons Attribution 4.0 International License.