Darktable shadows and highlights vs tone equalizer

Ariel_Di_Miro · February 27, 2022, 2:36pm

Hi!

I have just given a try, basically trying to use the recommendations / methods of Boris Hajdukovic as well as I can .

190918-T10X2232.raf.xmp (14.1 KB)

Best regards
Ariel

Dean · February 27, 2022, 2:54pm

Did you try setting “preserve details” to none? I know it sounds counter intuitive but turn on the mask setting and then turn on and off preserve details and I think you will see something interesting.

priort · February 27, 2022, 4:00pm

Is that a custom plugin or one that comes with Gimp or gmic??

david · February 27, 2022, 5:21pm

It is a custom plug-in which I created. It creates multiple layers each of which has a mask. Each mask is effectively a “zone” of luminosity, but with a small amount of overlap between masks.

priort · February 27, 2022, 6:15pm

Ah yes I have seen this done I think Pat David did a Gimp article back some time ago and Michael Davies has as well.

Claes · February 27, 2022, 7:12pm

In case you are interested, here it is: GimpScripts: Equal Luminosity Masks Ver. 1.2

Have fun!
Claes in Lund, Sweden

david · February 27, 2022, 9:08pm

@priort
I used the Pat David luminosity masks (as scripted by Saul Goode) for several years. Eventually this plug-in stopped working - I think as a result of an upgrade to GIMP. That started me on a long journey to create my plug-in with much help from other people.
It is more akin to the Ansel Adams zone concept, in that it makes ten equal independent masks ranging from the darkest to the brightest parts of the image. A copy of the original image is stretched to the full dynamic range and then divided into ten “chunks” to create the masks. The division is done with curves so that there is a slight overlap between masks otherwise it would be impossible to achieve a blend at the transition.

All the usual controls - hue, saturation, contrast, brightness, curves, etc. can be used on a masked channel without affecting the adjacent ones.

I also find it useful for solving difficult masking problems, frequently using the created masks in combination.

The latest version (Revision 10) can be found at Updated Luminosity & Saturation mask plug-ins - GIMP LEARN

priort · February 27, 2022, 9:30pm

Thanks for sharing…

Tim · February 27, 2022, 11:11pm

@david, I honestly think this is the best edit of this image, so far.

Matt_Maguire · February 28, 2022, 2:52pm

It used to be in the user manual, but seems it was removed. Not sure when that happened, but here is a link to page where it used to be mentioned why the use of shadows and highlights is not generally advisable:

github.com

darktable-org/dtdocs/blob/5334b89a5e27e5bc912dfefa90f49d13aff38d0d/content/overview/workflow/edit-scene-referred.md

---
title: "editing an image: scene-referred workflow"
id: edit-scene-referred
draft: false
weight: 30
author: "people"
---

The _scene-referred_ workflow places an emphasis on performing image processing in the linear scene-referred part of the pixelpipe. This helps to reduce artifacts and color shifts that can result from processing non-linear pixel values and, by decoupling the image processing from the characteristics of a specific display, it makes it easier to adapt your work in the future to new display media, such as high dynamic range displays.

This being the recommended way to process images in versions 3.0 and above, this section will provide a much more comprehensive overview than the next section on the _display-referred_ workflow.

# basic steps
Basic image processing in scene-referred workflow requires you, as a minimum, to consider the following steps in order to render a reasonable image on your display:

capture an image
: Use your camera to take a properly exposed image. Normally you can rely on the camera's metering and automatic exposure features. However, for some scenes you may need to use the camera's exposure compensation dial to get an optimal exposure. In general, you want to make the exposure in camera as bright as possible without clipping the highlights. This is known as "exposing to the right" (ETTR), and it ensures you take best advantage of the sensor's dynamic range. Many cameras have features like "zebras" or "blinkies" to warn you when you are in danger of clipping.

[_exposure_](../../module-reference/processing-modules/exposure.md)
: This module is enabled by default, and it will include an initial exposure boost of +0.5EV to mimic the standard processing of most in-camera JPEGs. The metering systems in cameras vary, and some camera models might need a slightly larger exposure boost (eg. +0.8EV ~ 1.5EV), in which case you can create an auto-apply [preset](../../darkroom/interacting-with-modules/presets.md) as required. The exposure module will detect if the camera's exposure compensation dial was used (see above remarks about ETTR), and will re-adjust the exposure accordingly.

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elstoc · February 28, 2022, 3:02pm

Yes I think you wrote that originally, based on the RGB article. But still it doesn’t say “that shadow highlights is bad and never to use it”. I don’t ever recall seeing it stated in such black & white terms. That text was replaced with the new processing guide we wrote last year but such warnings are now in the module reference sections of the user manual.

dirksagwitz · February 28, 2022, 5:13pm

I gave it another try …

190918-T10X2232_02.raf.xmp (10.5 KB)

anon41087856 · February 28, 2022, 11:37pm

It’s really not what it is about.

Shadows and highlights shift shadows to muddy blue because it works only on the L channel of Lab space, that is at constant chroma in a space that has problems in the blue area. Working on shadows should be made at constant saturation, aka through an exposure compensation.

Darkening at constant chroma makes colour go past the greyness boundary and may produce out-of-gamuts. See Engineering | Color saturation control for the 21th century

The colour model used for this purpose is not suitable. Tone EQ on the other hand travels at constant saturation, so any colour in-gamut before is guaranteed to be in-gamut after, and there should be no colour shift because it’s simply exposure.

Terry · February 28, 2022, 11:54pm

Thanks Aurélien for your considered and polite response. I am truly appreciative of the work you do with Darktable and how you bring a totally new approach to the processing. I love your work with Filmic and the Tone Equalizer. I also love the new modules you are creating. Keep up the great work. Your understanding of color science is amazing and the fact that you are now working on Filmic V6 means that you continue to learn and improve your own tools. Have a great week.

anon41087856 · March 1, 2022, 3:50am

Using tone EQ on gradients is misleading. The masking is meant to isolate foreground from background while following edges, based on contrast detection. There is no point for masking if you have a a smooth gradient like that, in this setup, tone EQ will behave like any tone curve with simply a different interface.

And why should S&H be the reference here ?

Take a picture with some vivid colours and sharp objects in back lighting, you will see how S&H will damage your colours.

We only understand algorithms by looking at how they fail.

dqpcoxeas · March 1, 2022, 4:40pm

My version…

190918-T10X2232.raf.xmp (27.8 KB)

David_Prescott · March 1, 2022, 6:25pm

love this version except for the sky which is murkier than the reflection

dqpcoxeas · March 1, 2022, 8:24pm

It has a trick… the reflection changed places.

herbert-50 · March 1, 2022, 10:40pm

It is not the reference, but one of many possibilities.

The tone equalizer is recommended as a replacement for shadows and highlights.

But I can’t get the same result as with shadows and highlights.

I also can’t get the same result with it as someone else did with the Tone equalizer unless I know the individual values for the sliders.

I think this is due to the setting of the mask.

But I probably just don’t have the experience here. Nevertheless, I find it very difficult in contrast to other modules.

The algorithm of shadows and highlights may be worse and work in non-linear color space. But the module is simpler and if I like the result for a photo, then why should I use the more complex module.

anon41087856 · March 1, 2022, 10:48pm

It’s simpler because it takes shortcuts, and those shortcuts will come back in your face when you least expect it. Broken clocks still give the accurate time twice a day, doesn’t mean you should trust them in general.