I see what you mean. Yes, this is a great way to see the difference between several snapshots that can be saved after accepting several calibration strategies. But how can we see these differences in connection to reference values of the official chart? This is what may interest us most if we want to achieve scientific precision (which is, I agree, not needed for most of the users. This is for those who look for the closest colors to the original.)
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Also just curious why not have another optimization strategy in this module for magenta patches which can be extremely difficult to tweak for most cameras? Skin tones, sky and foliage colors do the job but there’s no magenta. Just a thought.
because that’s not implemented. Each optimation needs to be implemented, and if the developer didn’t had such optimation in mind it wasn’t implemented. It’s just a result of priorities… and time
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Y’know, the 24-patch ColorChecker is a rather limited source for dE assessment. How 'bout references like the Munsell or Lippman spectral datasets, more access to appropriate patches of colors relevant to specific needs, e.g., skin tones.
dcamprof has a test-profile command; haven’t messed with it much, it can bang a profile against a .ti3 file of spectra and produce such dE TIFFs…
Well I think the dots in the color checker are the reference values so before you apply you can see how far off you are visually and again once you apply the calibration you can see how much closer they are… also the graphic overlays show good fair and poor matches… but not the numbers ie delta E per patch
Yes, I know. It does almost what I suggest but you can’t do a quick assess of different strategies without making screenshots. If I need to compare 5 strategies or 10 strategies this may become a nightmare. And those white frames and diagonals do not allow to visualize the whole picture at once. As a quick compromise if DT could allow users to switch off the white lines and make dots the size of square (with one click or a hotkey). I mean toggling the frames on and off. This will help improve the visualization process a little.
Like this
**Note: Also it might help to adjust white and black points visually by looking at these squares. Which is now problematic because of the white frames. See how easier you can distinguish the colors without white frames.
And it would be much easier if we could generate synthetic comparison charts before accepting calibration **
But having a set of exact standard pictures of any number of comparison charts will be much better anyway.
From this point we’re starting to move from a small hobby with DT to a large national museum full time projects taking a lot of money and efforts )))
That’s interesting; I was proposing using the FOSS tools that already exist, no extra development, no extra cost.
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I’m now playing with dcamprof. I have a problem. Scanin just doesn’t work for me. It doesn’t recognize patches correctly. Looking at *diag.tif file I can see this (NOTE: I made it lighter here)
Some patches are overlapping. Is there any GUI for linux to apply overlay pattern on the image?
Unlike darktable’s workflow the “Rawtherapee → tif file → dcamprof → Rawtherapee” approach looks much longer and just awkward. Any suggestions how it can be simplified?
Even without any extra development DT solution looks more usable. Unless I make dcamprof creating more precise profiles, I see no reason to use it yet.
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Are you using the right cht or definition file for the version of the color checker that you have??
Sure. I’m experimenting with a photo of my spydercheckr48 and use this command line
scanin -v -dipn 02.tif /usr/share/color/argyll/ref/SpyderChecker.cht /usr/share/color/argyll/ref/SpyderChecker.cie 02-diag.tif
cht and cie files are from argyll. They look authentic to me.
This is a minified diag file
ADDON: just found this:
scanin: /usr/local/lib/libtiff.so.5: no version information available (required by scanin)
Scanin, Version 2.0.0
Author: Graeme W. Gill, licensed under the AGPL Version 3
Looks like I have a libtiff problem. Any clues?
Kudos go to you for trying dcamprof. It’s my go-to for all camera profiling, to include making profiles from spectral data for the camera.
Yeah, command line is a pain. I guess since I’m old enough to be Dennis Ritchie’s younger brother it’s like second nature to me, so I have to temper my irk with the GUI crowd, present company excepted 
For me, the dE text reports are good enough to evaluate ColorChecker-trained targets, I even wrote in my profile script to sort the report on dE (see, there’s that command-line angst… ) I did peruse the dE TIFFs at the start, but soon got to know from the numbers what’s good and not-so. Max dE <= 5 is IMHO good enough for target shot profiles, IMHO; for my spectral profiles it’s < 3.
The dcamprof author used the dcamprof code to make a GUI version, Lumariver. It’s commercial software, but one of the few softwares I’d actually recommend buying. Don’t know how Anders presents the dE data, here’s the manual page for you to investigate:
https://www.lumariver.com/lrpd-manual/
It may be there’s appetite to put dcamprof wrap-around code in darktable. I’m not a dt dev, so that’s probably presumptuous on my part.
Oh yes, scanin can be a bit fiddly. Nothing to offer there except to shoot as square-on as possible, and crop to put the registration marks just inside the image corners.
I’m not that mature as you but typing a couple of commands or creating scripts of any sort under linux isn’t a problem for me. Scripting might improve our life once you have created your own workflow )))
Under ‘crop to put the registration marks’ you mean white lines for colorchecker and white dots for spydercheckr? Like these?
BTW, Spydercheckr 24 (no case version) doesn’t have any marks
Hmm, that’s where the marks are, but mine on the Passport are little 'L’s…
Putting them in the corners also implies the target is square-on in the image, so rotating it to line up with the edges is also good…
I’m having Max dE ~ 5 for Spydercheckr48 and Max dE ~ 3 for Colorchecker Passport under DT. But these are just numbers. Visualization gives you more freedom.
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No, it doesn’t work. I’ve adjusted perspective and added some space for white marks.
Scanin doesn’t see these marks. It tries to recognize the borders of the patches as you can see. It puts reds L but in wrong positions. Maybe it may work better with Colorchecker but I prefer spyder.
I’m going to give this approach a rest. I’d better spend more time improving my DT workflow. I think there’s still more room for this.
Thanks anyway )
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I put “-F 146,254,3814,262,3815,2410,138,2401” key to scanin command and it works now. These are coordinates of the fiducual marks (Look like cht file has wrong values). Anyway it works now, but calibration didn’t go well enough in terms of white and black points and colors looks ok.
It took me ages to manually grab coordinates )))
Just a quick question for you. When do you adjust exposure? In DT you can adjust exposure before calibration and it helps. How it can be done for dcamprof?
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In the camera, I go for a solid ETTR. So, I’ll usually shoot a 3-exposure bracket, take the highest one that doesn’t blow any highlights, even the fiducial marks. It’s better to underexpose than to blow anything…
I don’t do any adjustment in post except for black subtract and white balance. I even use a half demosaic, doesn’t change the channel values like the others will.
With dcamprof, I’ve even played with doing white balance chromatically, by not white balancing the target shot and letting the profile do it Works, but one really needs to do the target shot in the same light as the scene so it’s a bit cumbersome.
I’ve managed to write a small bash script for linux users and owners of spydercheckr48. If you crop target image exactly to red dots and run my script it’ll prepare coordinates for scanin program for correct patch recognition.
If someone needs it…
# Save this as make_DCP_for_SC48.sh
#
# Generates DCP profile for Rawtherapee (for Spydercheckr48 owners and latest Argyll)
# Usage:
# ./make_DCP_for_SC48.sh target_file_name.tif
#
base=`basename $1 .tif`
arrIN=`identify -format '%w %h' $1`
arrIN=(${arrIN// / })
w=${arrIN[0]} ; w="$((w-1))"
h=${arrIN[1]} ; h="$((h-1))"
fiducual="0,0,$w,0,$w,$h,0,$h"
./scanin -v -F $fiducual -dipn $base.tif /usr/share/color/argyll/ref/SpyderChecker.cht /usr/share/color/argyll/ref/SpyderChecker.cie $base-diag.tif
# Following depends on your configuration
# dcamprof make-profile .....
# dcamprof make-dcp .....
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