> Quote - Rendered with default gamma, result measured in Photoshop: 82% brightness.

Right here, you went totally wrong. The value is not 82% - let's be explicit. The value is the integer 208. The luminance represented by this number, 208, is not 208/255 - that would be a linear interpretation, and the colors on your screen are NOT LINEAR. Your monitor does not agree with you that it should emit 82% of its max brightness given an input integer of 208.

Instead, the brightness is exponentiated by 2.2.

The brightness emitted by a pixel set to 208 is (208 / 255) ** 2.2. That would be .64 of the maximum brightness.

Given that the source (max white box) is transmitting here through an 80% transparent box, the resulting 208 is absolutely correct to cause 64% of that whiteness to show up on your computer screen.

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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)