Base Curve Module “Hybrid” & ACES - Like (Proof of Concept)

Software darktable
81

I have same issue with Mac_intel.
update: thank you
libre-dt-lab-ba33703b31-x86_64.dmg is working without crashing.

82

Funny … same version as you .
But crashes as soon as I do activate the " base curve " module …

Bildschirmfoto 2026-04-25 um 20.14.07
Bildschirmfoto 2026-04-25 um 20.14.07572×434 54.2 KB

83

Hello,

@helgeschneider @siamak
I’m sorry, this is a backward compatibility issue (introspection).

I don’t have time right now to fix this, and I think the best solution is to delete the configuration directory and all the .lab.xmp sidecar files.
Edit,
I just tested by copying and pasting a section of code to create a new version.
I recommend that you download the new version before deleting your database.

I’ll get back to you later with more details about the new curve, which is giving me excellent results.
I’ve uploaded a new version

Greetings from the Luberon,
Christian

84

Thanks. libre-dt-lab-ba33703b31-x86_64.dmg works on my osx_intel.
BTW, never kept sidecar files.

1 Like
85

Hello,

Have you tested the latest version, d3b164eb47?
Thank you for your help,
Christian

86

Hello,

I would like to introduce an update to the Base Curve module: the addition of a third curve, “Cinematic DRT”, loosely based on OpenDRT.

Cinematic DRT (mode 3) is a Display Rendering Transform (DRT) operating in the Oklab color space (UCS). It is designed to deliver organic rendering without hue drift, even under heavy dynamic range compression.

Key points:

Pre-compression Brilliance : To avoid the “neon” look of highly saturated colors (flowers, LEDs, neon signs), the module intelligently reduces their intensity before tonemapping, proportionally to their saturation. This is the Pre-tonescale Brilliance concept borrowed from OpenDRT.

ACES Tonal Mapping : This mode uses the rational approximation of the ACES curve (Stephen Hill / BakingLab). A +0.25 EV compensation factor (1.189f) is applied to correct for the curve’s natural density. Shadow lift and highlight gain are integrated directly into the curve’s power equation for smooth, artifact-free transitions.

Saturation Gate : A mechanism that reduces saturation proportionally to the compression applied by the tonescale: the more a pixel is pushed toward the highlights, the more it loses color. This guarantees clean, neutral whites even under strong contrast : no more cyan skies or yellowish skin tones in overexposed areas.

Perceptual Saturation Boost : A new slider that boosts saturation in the midtones within UCS space, while protecting areas that are already heavily saturated. Its behavior is similar to a vibrance slider.

UCS Saturation Balance : A sigmoid centered on middle gray is used as a tonal mask. It allows selective saturation of shadows while desaturating highlights (or vice versa), simulating the analog film rendering where highlights naturally lose their color.

Highlight Roll-off : A final stage that progressively desaturates pixels exceeding 80% luminance to ensure a smooth transition to display white. This roll-off was previously hard-coded in the module; it is now a slider available across all three modes.

Capture d’écran du 2026-04-26 21-27-39
Capture d’écran du 2026-04-26 21-27-391920×1080 1.31 MB

Sources and Technical References

Greetings from the Luberon, :herb:
Christian

4 Likes
87

You have been busy…:grin:

2 Likes
88

d3b164eb47 working on some images specifically dng. I will continue testing and report back.

Update: As you earlier mentioned it. It had to do with the backward compatibility. I do not save xml files for any of my raw images at all.
In this case before taking any drastic measure, I did delete the history stack and the crashing stoped. Now I can activate the base module without crashing as well.
However, I continue to test and will report of any issues.

Thank you again @Christian-B

1 Like