What's the difference between:

ART 1.17.2

What the difference between:

  • 1st tab: exposure + tonecurve-contrast
  • 3rd tab: LAB adjustments: lightness + contrast

Where the “better” way to change the darkness/lightness of an image and the contrast?


There are several differences, more than I understand (and as always, I’m waiting to be corrected :slight_smile: ) but here are a few:

  • Changing Exposure will affect saturation (being RGB), while changing lightness in Lab* will not since luminosity is decoupled from color in the Lab* color space.

  • The tone curve allows for much more specific adjustments than just darker / lighter. It can be used to darken some areas while lightening others, effectively change white / black points, for example.

  • L*a*b* lightness and contrast can be used to make tonal changes with less side effects on color, and vice-versa.

As an example, here’s a heavy-handed illustration of a similar adjustment using Exposure and Lab* Lightness.

Original image

Exposure adjustment down

L*a*b* Lightness adjustment down

Exposure adjustment up

L*a*b* Lightness adjustment up

Note the histograms of the altered images are pretty similar but the colors are different. There’s more (different?) color shift with Exposure.

Personally, I use Exposure to prevent clipping and more or less center the histogram in most cases. I’ll add some Log Tone Mapping Highlights Precompression to tone down isolated highlights if needed. Then I’ll use L*a*b* Chromaticity to add back a little color if needed. I find that I rarely tweak tone curves anymore, but that may be more a reflection of what and how I shoot / process. OF course fdepending on individual images and all, there are many variations and / or other tools and approaches.

There’s no doubt there’s more than one way to do many things in ART, just find what works for you. RawPedia has some information that might be useful.

OK – Those of you who are smarter than me, please correct me. :smiley:


I didn’t realize that. But somehow I’ve been using the much more often the Lightness in the LAB. For the clipping, instead of exposure I tend to use the tone equalizer.

Thanks for the great info.

If all I’m trying to do is drop a few highlights down enough not to clip, I find the Log Tone Mapping Highlights precompression slider works well. It drops affects the upper end of the histogram without impacting anything else. You can also use the Target gray point slider in LTM to adjust brightness.

Using Black relative exposure and White relative exposure in LTM allows you to move the lower and upper bounds of what’s considered black to white. So for example, lowering white relative exposure relatively raises the highlights and vice-versa for black relative exposure. If I understand correctly, what that’s doing is setting the lower and upper tone boundaries for the transition from linear to perceptual (display) space.

Maybe? Someone please correct me. LOL

At any rate, these tools allow for more targeted adjustments.

Interesting. Before, I don’t think that I have ever used it.

I just tried, it can do the job but it’s a different way of thinking about it. I’ll see if I can get used to it.