Comparing Darktable and Capture One input color profile for Sony A6000

[guyru]

Hi,

Darktable does not have a profiled input color profile for the Sony A6000 camera. So, I’ve extracted the input color profile shipped with Capture One Express Sony (comes free) and decided to compare it with the input color profile that comes with Darktable. I thought it might be of interest to other users as well, so here it is. Images ending with _01 are the ones with the Capture One color profile.
I’ve kept post-processing to bare minimum (only applied levels on some images, didn’t apply lens correction which is probably needed) and exported before and after applying the input color profile. I’ve also used the unbreak input profile module with linear=0.05 and gamma=0.45.

I would say it provides a more pleasing result that the default Darktable profile. It seems that the Capture One color profile provides more “pop” to the image, and also noise looks somewhat less harsh (no noise reduction was applied to any of the images).

Apperantly, new users are limited in the number of pictures they can upload. Some more images are available in here

[heckflosse (Ingo Weyrich)]

IMHO the _01 images look worse than the others. They have more “pop”, but for me the colours are less natural. Just my 2 cents…

[sankos]

I actually prefer the C1 hues (maybe not so much the saturation), especially the blues of the skies – the standard matrix profile has too much magenta in the blues for me, which is my pet-peeve with input profiles.

Did you use any base curve? If so, I think it might be a bit too contrasty for the C1 profile, and since the base curve module operates in RGB values, this causes the slight oversaturation. The darks/shadows are possibly too compressed/blocked and could use some lightening, I think.

An interesting point about the noise difference – I wonder if it’s because the standard profile is of a matrix-type, and the C1 profile is a LUT one?

[sankos]

Incidentally, I also experimented with C1 profiles with my Pentax K10D and Nikon Coolpix A, and sometimes I prefer the C1 profile, sometimes my custom DCamProf profile. Both need a different base curve –C1 employs many curves in its processing (only one of them is embedded in the icc); my DCamProf profile uses a typical Adobe curve. I use the same unbreak profile settings as you.

[guyru]

Did you use any base curve?

I used the “sony alpha like” base curve. Would you recommend any other one?
Is there a way to convert the curves that come with Capture One (fcrv files) to darktable curves?

[sankos]

I used the “sony alpha like” base curve. Would you recommend any other one?

This curve is optimized for the default, linear, matrix profiles, so if you use an input profile like the one from C1, with its own embedded curve (which has a small dip in the lowest part), the contrast is likely to be too much.

You could design your own curve following the ideas in this post, or you could use the LUT module. Or you could do it by hand, using the darktable’s color picker and making a set of sample points from a photo of a colorchecker chart (e.g. the IT8 chart used by DPReview in their studio scene comparisons) – note the mean L values of the 24 White to Black wedges in the Lab readout and compare with the file rendered by C1. Then modify the base curve accordingly (it’s better to switch the curve view to logarithmic scale in order to have greater control over shadows). Save it as a preset, and the whole could be made into a style which you can apply automatically on import, etc.

Is there a way to convert the curves that come with Capture One (fcrv files) to darktable curves?

I don’t know if that’s possible. Anders Torger (the author of DCamprof/Lumariver) reverse-engineered the C1 curves but I think they are camera-specific.

[guyru]

Or you could do it by hand, using the darktable’s color picker and making a set of sample points from a photo of a colorchecker chart (e.g. the IT8 chart used by DPReview in their studio scene comparisons) – note the mean L values of the 24 White to Black wedges in the Lab readout and compare with the file rendered by C1. Then modify the base curve accordingly (it’s better to switch the curve view to logarithmic scale in order to have greater control over shadows). Save it as a preset, and the whole could be made into a style which you can apply automatically on import, etc.

I’m not quite sure I understood how to do what you meant. I’ve found the ARW files with the color checker target and the gray scale target from DPreview. But what should I do with them?

You could design your own curve following the ideas in this post

It seems the process to create a basecurve is invariable of the input color profile (am I missing something?). If so, how such new curve will better match the C1 color profile?

It seems that th

[sankos]

I’ve found the ARW files with the color checker target and the gray scale target from DPreview. But what should I do with them?

If you want to get similar contrast in darktable as in C1 follow these steps:

1. First, convert that ARW file in C1 and output as a tiff.
2. Then open the same ARW file in darktable and apply the C1 input profile + the unbreak profile module. Reset the base curve to linear. Then use the color picker: take live samples from the greyscale ramp which are representative of the whole spectrum of tones (sample an area rather than a point, set it to Lab space, mean value).
3. Then open in darktable the C1-processed tiff and sample the same patches. Note down the values of the L channel for each sample.
4. Go back to the raw file and use the base curve module to modify the L values so that they agree with the L values in the tiff file.
5. Save that curve as a preset to be used only with the C1 profile.
6. Test this curve on real-life photos. If the curve is very strong there might be some oversaturation issues, so you could consider using the Tone Curve module instead of base curve and modify the L channel only (with some slight steepening of the *a and *b channels to get some saturation so that it all looks good to you).

[guyru]

Go back to the raw file and use the base curve module to modify the L values so that they agree with the L values in the tiff file.

Is there way to specify values numerically like a LUT and let it create a curve automatically? It will make the process much simpler.

[sankos]

The Kodak Gray Scale chart which DPR use in their studio scene has these reference values as a guideline (mind you that those values will give you different tonality than in C1).

When it comes to translating those into an automatic curve I’d also be interested if there’s an easy solution.

[guyru]

I managed to get the grayscale on the Colorchecker to match. But when I tested it on the Kodak grayscale, my basecurve didn’t hold up. It seems that it was over-fitted for the color checker.

However, while working on it I learned/found to good things:

1. You can hover the mouse over the nodes in the basecurve tool and adjust them using the arrows. If you hold down the Ctrl key, adjustments will be in increments of 0.01 which allows easy fine-tuning.
2. Someone created basecurves for Sony A6300 which has a similar sensor. They work better that the built-in “sony alpha like”.

[asn (Andreas Schneider)]

As darktable-chart creates a curve based on the gray ramp of a color checker I’ve just used what it produced:

https://blog.pixelbook.org/2018/10/sony-alpha-7-iii-basecurve-and-camera-profile-for-darktable/