Here is a graph of the ETM function for various exposure values, and a gain of 1.0. (Click it)

The bold line is Exposure=1.6, the default.

The bottom is Exposure = 1.0.

The top is Exposure = 2.2.

There is no such thing as a "do nothing" Exposure value.

This function never reaches 1, no matter how big x is.

The purpose of it is to map all values from 0 to infinity into the range 0 to 1. You can adjust the curve up or down, but you cannot change its shape.

An interesting observation, then, is that with ETM enabled, you cannot make a pure white pixel (RGB 255 255 255), unless you have a shader produce a luminance value in the thousands.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)