Exposure control in a raw developer: misnomer?

Started Jan 30, 2013 | Discussions thread
gollywop Veteran Member • Posts: 8,283
Re: Absolutely correct.

Great Bustard wrote:

dosdan wrote:

As I understand it, the "Exposure Triangle" is composed of Scene Luminance, Shutter Speed, Aperture (or should that be "F-number"?). These 3 alone determine the number of photons captured by the sensor.


ISO Sensitivity plays a role in the rendered brightness of the outputted image. (As well as helping to mitigate the contribution to the total read noise of the ADC noise floor in most cameras.)


So, I take the phrase "exposing a shot" to refer to the capturing process, not the rendering process. With in-camera JPEG, these two processes are combined. When shooting raw, the development process is separated and postponed.


But most raw development programs have an "Exposure" adjustment control. But isn't this adjusting the brightness of the rendered output? If so, it has nothing to do with exposure and is a misnomer.

So what should this control be labelled? "Rendered Brightness"?


Well, there is a distinction to be made. In the earlier days of ACR, Exposure was basically an ISO slider that essentially multiplied all values by a given amount, altering all values in the same proportion (and quite able to blow out highlights). The "brightness control," by contrast, boosted the mids while holding the ends fixed; it was more nearly like taking a "curves" and lifting the center.

Raw converters like RPP have a Compressed Exposure slider that multiplies the exposure values up to a point, but compresses the highlights in the top, say, 2 EV to keep the highlights from clipping.

Nowadays, ACR doesn't have a "brightness" control in the sense of above, but you can achieve the same end in a number of ways.

So, rather than call the "exposure" control Rendered Brightness, I'd rather see it called ISO, or gain, or Exposure Multiplier. It clearly increases the brightness of the image (and doesn't in any way affect the image's actual exposure), but it doesn't protect the highlights, which is what a "brightness" control ought to do.

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