My two cents (and that’s about all it’s worth). First, I don’t see any need to change the terminology, but if it just had to be done, the best suggestion I’ve seen so far is “gain”.
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Quite serious. Maybe “fortuitous” was not the best choice of adjective, but my point is that the association is borne out of expediency, and not from a sufficiently deep consideration of its inconsistency and, more important, its implications.
Not buying that, yet. I did a cursory review of some of the “authoritative” sources of definitions and didn’t find any that related the word “exposure” to the post-processing modification of the measured values, the operation we’re talking about here.
Here’s the thing. The “exposure” operation in software looks like this:
//Exposure Compensation
//
//Multiplies each R, G, and B value of each pixel by 2**ev
//
void gImage::ApplyExposureCompensation(double ev, int threadcount)
{
double mult = pow(2.0,ev);
#pragma omp parallel for num_threads(threadcount)
for (unsigned x=0; x<w; x++) {
for (unsigned y=0; y<h; y++) {
unsigned pos = x + y*w;
image[pos].r *= mult;
image[pos].g *= mult;
image[pos].b *= mult;
}
}
}
ref: https://github.com/butcherg/rawproc/blob/master/src/gimage.cpp#L4053C1-L4070C2
It’s essentially multiplying each R, G, and B value of each pixel times a number that represents a “stop”, owing to the old detents in lens aperture dials to reliably increment the amount of light let in by doubles or halves. Fancy Softwares might add embellishments like highlight-rolloff, but the above is the essential operation.
The key point is that the above IS NOT THE SAME THING AS CHANGING THE APERTURE AND/OR SHUTTER SPEED WHEN YOU TAKE THE PICTURE. Sure, it adjusts the values in the same scale, but the implications are different. Changing exposure setting before you take the shot changes the amount of energy to which the sensor is EXPOSED. Open the aperture a bit, more light reaches the sensor, particularly to the shadows, so less ambiguity in their measurement, resulting in less noise. Changing the “exposure” slider in your favorite software does not change the measured energy; whatever shot noise you captured at the scene is just multiplied, and a lot easier to see, dang…
I know why such a tool is in software; it’s one of the “carry-over” paradigms from film photography. Staring at an underexposed negative in the darkroom (I’ve done this, BTW), you think through how to print it so it looks okay. It’s all ass-backwards there, your underexposed negative is quite thin, so you back off on the print paper exposure time so those thin middle tones resolve to gray-ish. Cripes, probably have all that backwards, let me know. Deal is, you have a tool in the darkroom to adjust sub-optimal exposure decisions. Still have the same implications, not changing the sensor capture; you are changing an exposure, but it’s to the print paper…
My concern is this, and I’ve seen such played out in all sorts of situations: A person sees the “exposure” tool in their software, and concludes that if they underexpose their images at capture they can just simply slide this thing up to correct it. And then wonder why such pictures look terrible…
In rawproc, I named that tool “exposure compensation”. I originally called it just “exposure” like every one else, but I never felt comfortable with that. The more I think about it, the more I like my ultimate choice; adding “compensation” to the title gives it the proper context.
We can cogitate all the justification for the use of the title “exposure” to the corresponding tool, but it really isn’t clear communication. I"m a bit sensitive to such; I’ve previously stated my former day job in general terms, “aerospace engineer”. Where I actually practiced that was with The Boeing Company, 20 years as a senior engineer. We all became very sensitive to the need for clear communication in our recent travails…
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You are of course right, but I don’t think anyone suggested this.
You can pretty much do this to a surprisingly large extent with recent sensors. The concept is called “iso invariance”. Yes, you get noise if you go crazy with this, but in normal ranges it is fine. Eg even in mid-tier cameras from the last 5 years, if you expose at the base ISO and then add +2 EV in post-processing, the results will be OK.
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But we want to name it like it is… 
Oops, this post is a real philosophical treatise 
I’ve experienced this kind of discussion throughout my professional career in the bakery and pastry industry. 
As an amateur photographer, the term exposure suits me just fine.
Darktable is free software, so let’s give the developers of the various modules the freedom to name their babies.
Greetings from Brussels,
Christian
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In the past I came across this linked post in a follow-up search where someone had proposed in their comments that really the exposure slider was more of a post processing iso adjustment, ie gain to the signal… Looking for any nuance to that statement I came across the link above…
Your iso invariant comment reminded me of it…
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You don’t give your “authoritative” sources, but most I know are rather poor when it comes to domain-specific usages (to avoid the use of “jargon”). Which is why technical discussions between persons with different expertise can get “interesting” 
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https://www.merriam-webster.com/dictionary/exposure (See #4, a bit dated…)
https://www.britannica.com/dictionary/exposure (see #4)
https://www.oxfordlearnersdictionaries.com/us/definition/english/exposure (see #6)
Left out those that used the word in the definition, bad form…
Shouldn’t it be called “gain”?
Gain usually refers to a multiplication - either straight up or with some formula attached.
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'gain’is okay, I guess. Definitely drives home the nature of the operation.
I’m gonna stick with ‘compensation’. I like the semantics better…
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So I wonder what is really the correct term/description of what this slider adjusts?
I am just steadily in doubt as to what is the precise term for the change I make with the slider for amending the tones of an image towards white or black.
@EspE1’s questions have not been clearly answered. I don’t know the internals of darkspace, so I’m not sure exactly what the control does. I would hope that someone familiar with dt can give a definitive answer.
But assuming it multiplies the linear RGB values by some number, I would call the control gain. The parameter it modifies is luminance, and it leaves chromaticity unchanged.
We can demonstrate the effect using ImageMagick. (As always, that’s the software I am most familiar with.) I make an image with a single pixel, in linear RGB colorspace.
C:\web\im>C:\im\ImageMagick-7.1.1-20-Q16-HDRI\magick xc:RGB(10%,20%,30%) -set colorspace RGB -colorspace xyY txt:
# ImageMagick pixel enumeration: 1,1,0,65535,xyy
0,0: (16479,18361,12186) #405F47B92F9A xyy(64.1211,71.4433,47.4173)
The xyY coordinates of the pixel are (64.1211,71.4433,47.4173).
C:\web\im>C:\im\ImageMagick-7.1.1-20-Q16-HDRI\magick xc:RGB(10%,20%,30%) -set colorspace RGB -evaluate Multiply 1.5 -colorspace xyY txt:
# ImageMagick pixel enumeration: 1,1,0,65535,xyy
0,0: (16479,18361,18279) #405F47B94767 xyy(64.1211,71.4433,71.126)
After multiplying the RGB coordinates by 1.5, the xyY coordinates are (64.1211,71.4433,71.126). Note that x and y are unchanged, but Y has increased by 50%.
Perhaps a similar demonstration can be done within darktable.
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That makes the most sense to me. I always viewed the control as analogous to exposure compensation by adjusting ISO.
My anecdotal evidence would suggest the complete opposite, I’d like it if the old “fix it in post” gag was still more of a gag than a technique that’s gaining legitimacy, but I think most beginners understand the capture and the post processing are very separate stages in a photographers workflow.
Is exposure compensation not a dial on your camera you use to tell your camera’s light meter that you’d like adjustments to be made? I think “Compensation for a less than perfect exposure” would be even clearer.
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(Yawn)
While I’m all for exact terminology, isn’t this getting a bit … extreme… (I had another word in mind, but…)
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You are welcome to not participate. Me, I found the discourse useful to re-visit a topic I didn’t understand as well back when I first considered it. Didn’t change my conclusions, but I understand the implications a bit better.
@EspE1 's original question was one of those “exposure triangle” rabbit holes, oft argued but still poorly understood IMHO. If we avoid discussing such to keep the peace, where do we really learn, then??
Done for now, in the woods, lightly snowing, time to go capture some compositions…
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Thanks for responding to what the question was about.
Well, I’ve begun to think that under my question of which parameter of an image is changed by the exposure slider, is a deeper philosophical question that ought to be addressed:
When does an image begin to exist?
Whatever parameter of the data of an image we’re changing by the program’s math, as user of an image processing program we can only directly observe its impact on the image as it is rendered on a screen or on a printed medium - which is the way we really work. This relates to the aspect I’ve touched upon as to whether the term used perhaps ought to be decided from a perceptual point of view. (Which should in this case likely lead us to “brightness” or “lightness”, the words most commonly used in this connection.)
“Luminance … describes the amount of light that passes through, is emitted from, or is reflected from a particular area”, but prior to any such rendering there is no such “area”.
Rather than me trying to say something wise about Kant’s “Das Ding an sich, Das Ding für mich”, I can just recommend:
“What the F*ck is a Picture?” in The Hitchhiker’s Guide to Digital Colour
which addresses some fundamental aspects of images.
(Warning: The meaning of the term “Scene” may possibly be read in new light afterwards … )
Although some of the discussion in this thread has come to address the naming/labeling of the Exposure module, and furthermore include some more camera-near aspects, topics I originally wasn’t concerned about, it’s anyway been lots to learn, as it luckily so often is in discussions here in the forum, so thanks to all that responded!
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Take a look around you. You’re making a continuous stream of images with the ‘camera’ shoe-horned into your head. What it’s using as a starting point is a ‘place’, with it’s attendant masses and energies. Pick up a camera and make an exposure, and your now engaging another imaging system that will eventually puke another picture for you to regard. I personally think the image is the rendition, the final product of whatever imaging system produced it, and the decisions we make to control the process.
I think Troy’s objection to the concept of a scene is with it’s intermediate-ness between the place and any rendition we may concoct. “Image-as-text” makes a lot of sense to me, with any means of imaging we’re just trying to describe where we were…
You keep asking these questions… 
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In a digital imager: when photons striking the sensor begin to increase the charge in the photo-sensitive elements, excluding shot noise, IMHO.
Is there room here for a thought about “latent image”?
Do you think an analog picture also begins when photons strikes the silver-bromide crystals, or when the film is processed?