What's the difference between

Software ART
1

art 1.19.3

What’s the difference between exposure compensation and lab adjustment > lightness?

Thanks

2

Here is the pipeline (the sequence of processing steps) used by ART. The modules are applied top → bottom:
https://bitbucket.org/agriggio/art/wiki/Pipeline

As you can see, exposure is applied before Lab adjustments, and it’s applied in linear RGB. The effect is very similar to increasing exposure in camera: sensor values are multiplied / divided by 2 for 1 EV of compensation. You will not perceive that as doubling brightness, as human vision is not linear.

Lab is a non-linear space, intended to somewhat reflect human perception. I do not know if ART clips Lab L at 100% or not.

@agriggio, ART’s developer, will be able to answer all your questions.

3

There’s also a small bit of verbiage from @agriggio in the ART reference manual (on the ART website) in each tool’s respective description. I’m not equipped to elaborate on what he said. LOL

4

Some uneducated guesses from me…

The Lab-Lightness slider behaves like a curve. That means raising it will give you something like this:

grafik

As you can see it doesn’t touch the white and black points. And of course it only works in the lightness channel, unbound from the colors.

Exposure will affect the whole histogramm and therefore also move the white and black point.

5

So which module would be the better place to set the black and white points?

Thanks

6

I have never cared about any points. I think the tools in the exposure tab and the lab module will just give you different looks an you should use the ones that give the result you like most. (yes, that’s the unsatisfying default answer)

I personally use exposure compensation for basic brightness of the photo, tone-eq for more detailed adjustments, and then I prefer lab-contrast and lab-chromaticity over their corresponding tools in the exposure tab.