Do you know if darktable has a ligthness control tool?


(Roger) #1

Hi,
Do you know if darktable (DT) has a tool for managing the lightness in a photo as ACDSee does with the LightEQ (www.acdsee.com/en/lighteq) or Capture One with the Luma Curve (blog.phaseone.com/tag/luma-curve/)?

In short words it is a contrast tool that adjust the lightness without modifying the colour.

The DT’s videos that I had seen shows such adjustments made by masks (in a Photoshop style) but this method is very unproductive and produces unpredictable results when other adjustments are made as you can see in this video (www.youtube.com/watch?v=aU8z81INOBU) where it took 40 minutes to get something that may require 40 seconds with the mentioned software.


(Mica) #2

The L channel/curve in the Tone Curve module is probably what you’re looking for. It works in the L*A*B* color space.

Use of the Luma tab of the Equalizer module or the Lightness tab of the Color Zones module will also yield pleasing results, depending on what exactly you want to do.


(Roger) #3

Thank you for your fast answer.
I am not able to get the expected results with the tools you mentioned. The tone curve>L apparently affects the contrast and equalizer>luma the sharpness.

Let me explain you better what I need:
Imagine you have an scene lighted with 8 spots, each one providing an stronger light, s1 is almost black and s8 is white.

You take picture 1 then you adjust s3 to be lighter and s5 darker and you take picture 2.

When comparing the pictures you will find a change in exposition around s3 and s5, not a changes of contrast or sharpness but steps of light.

In the linked video the scene is covered by a lot of masks and the light is adjusted in each one.

Instead, with the tool I am looking for, the shadows are automatically divided from black to white and you can adjust the light for each division with no further steps.

This is useful to emulate HDR, high speed sink / filling lights , recover shadows/highlights, de haze, etc.

Does darktable include a similar tool and if not, what is the channel to suggest it?


(Mica) #4

Perhaps the Zone System module? This divides your photo up into ~10 shades and then allows you to darken or lighten that particular zone.

Darktable is heavy on the masking, and it is a nice way to effect only what you want to edit.

You may suggest a feature here, but the ultimate destination would be the darktable bug tracker. Please keep in mind that a feature request is quite detailed, and a simple “copy this tool from another application” certainly will not be sufficient.


(Roger) #5

Thank you again.

May you provide a way to contact the darktable bug tracker?

The Zone System module is a nice graphic interface of the Tone Curve but it is linear, not asynchronous. This means each point must be bellow to the next otherwise the detail gets lost (or saturated).

The tool would work as the Color Zones module but using light instead of colour and following the picture histogram instead of the colour curve.

Returning to my example, if s2 has the same intensity than s5, the details remain, they both reach the same exposition. This is like using a filling light in a portrait or making a HDR image using many pictures with different exposition.

This feature is not a copy but the future, now there is only in a few products but it must be in all because it is faster an easier than the mask paradigm. Do you remember when the zone edition in RAW was criticised by the “experts” because they say such was related to the image edition? Now most SW has it. Additionally, the reviews about darktable claim it takes a lot of time to achieve the desired results, this may change that.

You may think that if ACDSee Pro and Capture One have what I want, why I am interested in darktable. The reason is I am moving from Windows/Apple/DSLR to Linux/MirrorLess and DT is better than the rest, including corporative and open source products…


(Mica) #6

https://redmine.darktable.org/projects/darktable/issues or you may want to discuss it in irc on #darktable on freenode

care you share some of those reviews?


(Roger) #7

Thank you. I will place my suggestion, lest see what happens first, darktable includes the Luminance module, Photivo supports Fuji X-System or ACDSee/Capture One come to Linux.

Here are plenty of comments about the subject. Note nobody says tDT is bad but time consuming.
https://www.dpreview.com/forums/post/59324818

In the meanwhile I am not able to move to Linux, spending 40 minutes in a picture instead of 40 seconds is a luxury that I can not afford.


(Roman Lebedev) #8

Have you read the usermanual?


Especially select by = lightness?


(Roger) #9

Yes and I used the tools. Had you?


(Mica) #10

He’s a developer of darktable.


(Roger) #11

Great!

May you both take a look to this crazy proposal and let me know your toughs, specially if it is clear enough:

Module: Exposures zone.
Purpose:
Adjust the luminosity in an image per zones making it possible to get multiple expositions at the same time. The result would be as if the processed photo would had been shot with multiple lights or as a HDR made with various images. This module would allow to easily create HDR images with a single RAW photo, and would be particularly useful with landscapes because there is no chance to use additional lights. In portraits, it would let to use less lights or to simple correct undesirable shadows.

Old process to replace: Currently, when the light (exposition) of a zone in an image has to be adjusted, it is necessary to create a mask to cover such zone, define its border to have a smooth transition and to apply the light adjustments (one for the whites and a second for the blacks). This process is time consuming because everything must be done for each zone, it requires good skills to manage the masks and better ones to apply the adjustments. It also produces unexpected results when additional effects are added to the picture, when the zones overlap or their transitions are not well made.

New process: The steps to adjust an image with the Exposures Zone would be: (Please compare this with the old one and its results).

  1. Exposure Zones.
  2. Denoise (Optional).
  3. White balance. (Optional)
  4. Colour adjustment.
  5. Clarity.

How it works:
First. Divides the image lightness from dark to light and shows how each division covers a zone in the image (as the Zone System does).
Second. Provides the controls to adjust the blacks and whites for each division.

Currently the histogram allows to adjust the blacks and whites for the hole picture and the Exposure Zones tool would make the same but on each division, giving the chance to make a zone lighter or darker that those around it.

Design: The shape may be as the Color Zones, showing in the background the histogram of the whites (the line made by the higher white value of each division) on top and the histogram of blacks in the bottom (the line made by the lower dark value of each division).
To adjust the whites and blacks, there would be two curves, one on top to increase or decrease the white values of each division and a second curve in the bottom to do the same with the blacks. There may be a colour picker to show what division we want to adjust.

Current examples in the market:
Capture One.- Luma Curve but it only adjusts the middle tone of each zone/division.
ACDSee Pro.- Light EQ provides full adjustment but by equalizer buttons and two curves badly implemented.


(Shreedhar Inamdar) #12

Will it be better if the developers have a tag Developer so that they are spared of some unintended aggressiveness from new comers because of their {usually terse} answers?


(Mica) #13

I don’t think so (my very personal opinion). I prefer to think that we are all one working towards improving the applications we have. We all help by utilizing the skills we have to enrich one another and the application.


#14

I agree with Mica.

Also: if one follows the forum for a while,
one will rather quickly get a grip of which
forumers are knowledgeable, be they devs or not.

Have fun!
Claes in Lund, Sweden


(Stefan Schmitz) #15

After decades (yup!) of forum activity, I think “knowing it all” isn’t the most important attribute of a participant. Knowing and admitting when you don’t is way more important.


#16

I don’t really understand what you are after, and I guess most of the others don’t understand your goal either. Maybe show some images that illustrate the effect you want.

PS: I don’t think you should use “HDR” in this context as it means something different than what you think it does.


(Roger) #17

Here is in action:

As you may note, this is an old tool but my suggestion is more advanced, The intention is not to make a copy but something better.

Exposure Zones would be nothing but a productivity tool. You can achieve the same results taking multiple shoots mask/layers or lights, but this needs a lot of time and good skills, as seen in this video (https://www.youtube.com/watch?v=aU8z81INOBU) May you say he is wrong? No, he simply took minutes in something that should be made in seconds.

I understand well my suggestion may be confusing for some people, but as you can read in this article related to Capture One Luma Curve: “once you start using it, you’ll notice you cannot work without it anymore” (https://fstoppers.com/originals/refine-your-images-contrast-simple-capture-one-pro-tool-178301), Luma Curve uses the same concept in a more primitive approach because it does not modify the blacks and whites, it only adjusts one tone at a time, this means a dark zone never could have the lighter value.

Dear houz: I hope you may now see how my suggestion do involves HDR, Please be aware it is asynchronous, while regular tone curves are sequential. Photivo already have a tool based in the same concept named “Dynamic range compression” (http://photivo.org/tutorials/fake_hdr), but this does not work by divisions as Exposure Zones would do.


#18
  • I asked for sample images. I don’t have time to watch videos.
  • Neither do I have time to read articles about other programs.
  • Changing the exposure in certain parts of an image has NOTHING to do with HDR. Even the link you give says so in the URL.

#19

As @LebedevRI already mentioned, the “Color Zones” works exactly the same as the video you have shared when its “select by” option is set to “lightness”. It has even more advanced features that let you process your photos more precise. It just doesn’t have an “auto” button that I don’t think is a big deal.


#20

Also I think the result of the auto button looks a lot like using the Shadows and Higlights module (also as @houz says this has nothing to do with HDR, sure some of the same techniques can be used to tonemap an HDR image but that doesn’t make it HDR)