difference between the Exposure, Black Level, and Brightness controls

Hello, if I study Raw Pedia, unfortunately I can’t find more detailed information on these questions: What is the difference between the Exposure, Black Level, and Brightness controls? All three have a similar effect on the image, making it lighter or darker - but what exactly do they do?

Can someone please explain this to me in more detail, or send me a link where this will be explained in detail?
Thank you very much in advance
micha

There is a point at which the camera’s sensor cannot pick up or record useful data. Black level is the lower bound set by the manufacturer and subsequently the user to clip it. However, it is not a denoise tool and can cause an undesirable colour shift.

Exposure is basically the doubling and halving of linear intensity. It is the easiest to understand because it coincides with camera adjustments of shutter speed, aperture, ISO and metering.

Brightness is more abstract because there are multiple definitions, implementations and applications of it. In contrast to exposure, it is less mathematical and more empirical, relating to the perception of light by our eyes, brain, and depending on the subject and surroundings.

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One thing I have noticed about RawTherapee is that there are often multiple ways to achive very similar effects. The devs seem to prioritize options and capabilities of simplicity and ease of use.

I too have often wodered the exact differences between tools.

I guess you mean instead of simplicity...

Well, we don’t do that for fun. We do that to stay backwards compatible with old processing (pp3) files. You don’t need to use all the stuff in RT. Just configure your favorites tab with the stuff you need

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There was a similar thread over at the Retouching forum of dpreview a few days ago. Interesting to me was to find out that LR apparently puts a tapering curve at the upper end on their exposure tool, to mitigate blowing highlights, I guess. I don’t like such; I want my software exposure tool to have the same semantics as my camera’s exposure compensation at the time of capture, and not do “pet tricks”.

It is my understand that light room is full of said pet tricks and “magic.”

prioritize ... *over* .... :stuck_out_tongue:

or, dare I say,
options and capabilities *are* simplicity and ease of use. :stuck_out_tongue_closed_eyes:

Clutter to you is treasure to me.@afre :stuck_out_tongue_winking_eye:

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Hallo afre,
thanks for the quick answer. But I still don’t quite understand when and why the black level control is used. I liked to use it to increase the depth of an image so that the black doesn’t just appear dark grey. Probably that was wrong. My question: When and why do you use this control Black?
micha

It wasn’t a complaint. It was just an observation. I appreciate all that you do.

I’ve used it in the past to crush shadows to make a lighter foreground stand out. I use a curve to do this sort of thing now, keeps some definition in the lowered shadows.

Hi!
You would check this discussion for the “get curves plugin”
https://discuss.pixls.us/t/get-the-curves-difference-between-2-images-like-get-curves-plugin-does/7626

This curve is the equivalent of +50 brightness slider in rawtherapee

This curve is the equivalent of -16384 black level (for some reason the saturation here doesn’t match)

This curve is the equivalent of a +1 EV exposure (check that button to apply the curve in linear gamma)

??? The black level is an offset, how could it be a curve ?

I recommend finding a low-contrast picture and load it with the Neutral profile. Then, play with slders and see the effect on the histogram. My conclusions are:

  • “Exposure” simply shifts the entire histogram without modifying its shape, unless it clips.
  • “Black” moves the darkest point without modifying the brightest point. The histogram gets stretched (which implies increased contrast).
  • “Lightness” shifts the histogram like “exposure”, except that it doesn’t let it clip, and it gets “bunched up” (reduces contrast) when you are near the boundaries.
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I seldom adjust black levels. In most cases, raw processors set them at reasonable levels. If not, consider submitting a bug report for your particular camera. Read more about black level here.

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Hello,
I have only changed the black value so far because it was recommended in http://rawpedia.rawtherapee.com/Exposure. = “Black Use this to set the black point. See the left side …”
You mean, you don’t have to adjust this value at all?
micha

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Ah, thanks for clarifying. This is a different black setting, related to tone compression. I was talking about raw black levels since that is what one usually refers to as black levels.

Hello,
sorry, the misunderstanding comes from the translations. I mean the slider in Exposure -> Black.
RT%20Exposure
When does it make sense to adjust this slider: Black?
micha

Here’s an example of an image where I crushed the shadows to 0,0,0 by setting a black point:

(I think I’ve posted this previously, but can’t find it)

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@micha Learn by doing. That is what I do anyway. There are plenty of #processing:playraw files for you to test this on. Try using it with Shadow compression.

Hello,
I thank you for all the hints that help me better understand RT. I also practice this learning by doing and I am progressing slowly.
Nevertheless, I would like to understand what the Exposure - Black control really does and when it makes sense to use it. Is there a clear answer?
micha