I have a Camera Calibrated DCP profile with a Linear Tone Curve that applies a LookTable.
I’ve been able to successfully build on top of this linear profile by crafting a 3D LUT which applies a contrast curve against J’ in CAM16UCS while holding M’ constant. I also guard against oversaturation, and generally I like the output.
I am now trying to modify the DCP directly to do the following:
Apply the sigmoid in the Tone Curve
Update the BaselineExposureOffset to hold middle gray pinned, after the sigmoid relocates it
Update the LookTable to properly prewarp colors before they hit the ToneCurve, such that after hitting the ToneCurve they match the colors of my old XMP profile (1. DCP Look Table 2.Linear Curve, 3. 3D LUT).
I must be fundamentally misunderstanding something in the DCP pipeline, at least in ACR, because my colors are not rendering correctly in the DCP.
I was wondering if anybody here has successfully coded up a custom LookTable to achieve target colors after the Tone Curve application?
I’ve done a lot of digging around on this, and have gathered the following:
1.The LookTable is applied before the Tone Curve, and can be used to prewarp colors as a defense againdt the Tone Curves color alterations
2. ACR applies the Tone Curve against the min and max channels, then computes the mid channel in a hue preservation attempt
3. If a LookTable is sRGB encoded, then to get the linear V of the HSV you have to inverse gamma the value
4. Overfitting the LookTable to meet specific output colors can result in artifacting and banding, so some amount of smoothing is suggested
5. The neutral axes, i.e S = 0% and V = 0% and possibly V = 1% are locked down by ACR and can not be adjusted by the LookTable. The Tone Curve controls these values
It was much easier conceptually to do the math in the 3D LUT, because all you have to do is apply the contrast curve and then gracefully gamut map back into ProPhoto. With the DCP profile, unless you actually understand the technical processing pipeline it seems impossible.
Any sort of direction on successfully creating the LookTable to achieve a specific target of output colors (per HSV input) would really help.
Hi and welcome! We focus on free and open source software here because we can know with certainty what it does to our images and allows us to modify and use the software was we see fit.
ACR, Light room, etc there is no way for us to verify what it does or how it handles a DCP.
There are a multitude of really good Free Software raw editors, like RawTherapee, ART, dark table, etc. That will handle a DCP and you can figure out what it actually does.
I have been going back and forth on using Darktable actually. I’m at the point where I know how to load an ICC input profile, I kind of understand how to “unbreak” it (but don’t get what setting is best here), and I know how to swap between filmic and sigmoid as the final tonemapper
I have a general idea on how to use the color calibration tool and to leave the legacy white balance tool alone
But i think the concept of masking, which seems to unlock the full power of tools like instances of tone eq, is confusing to me. I can conceptually understand at a high level how to mask in DT, butI have a hard time fine tuning and feathering, intersecting, etc
Maybe for that (and to grasp the best usage of the tone eq) i should watch or read some newer tutorials.
No offense taken, just that I don’t think you’ll get quality help for ACR/Light room here and to be honest, we are not really interested in having discussions about those tools here; we can’t really reason about what it does, we can’t share it freely with our friends, we can’t really make it ours.
I am glad you’ve tried darktable, there are a lot of experts here for that, and we have a lot if posts about LUTs if you do a little searching.
It’s a command-line program and you have to compile it yourself, but it lets you dig into the particulars of camera profiles both ICC and DCP. Even if you don’t use it, its documentation is priceless:
It honestly sounds like you maybe started at the “wrong end” when learning darktable. As you have probably figured out by now, it works very differently from commercial editors, so you need to start from the basics. My beginner guide has everything you need: How to Get Started with darktable, 2026 Edition — Nis' Notebook
But if you want to use DCPs, you will have to look at RawTherapee or ART.