Filmic RGB vs in-camera Exposure Compensation

[alpinist]

@kofa

I don’t know how filmic computes the white and black relative exposure. However, there is very good reason for the exposure compensation:
Suppose I’m in a room on a bright day. This is much darker than the outside. There is a window visible in the picture, with the bright view outside.
Now, if I take a picture inside, the camera will most probably expose for the majority of the image, properly exposing the room, but blowing out the window (completely saturating the sensor where the window is projected, losing all details). I can either spot-meter for the window, and later raise the exposure manually, or I can use in-camera exposure compensation to reduce exposure by say 2 or 3 EV. This will keep (some of) the highlights, but underexpose the room.
I import the raw in darktable; the exposure module reverts my manual exposure reduction, exposing the room properly. The window will go very bright, but in filmic I can simply increase the white point to tone it down, and recover highlight detail. (I could do the same / something similar in other raw developers as well.)

When I first stumbled across this thread I thought it’s only about automatic undoing of dialed-in exposure compensation. Only later I realized that the defaults in the scene-referred workflow do not simply undo the exposure compensation that was set in camera but at the same time adjust the black and white point accordingly inside the filmic module.

I am trying to improve my intuition for what is actually going on here.

@Matt_Maguire

Let’s say you set your exposure module to automatically set the “exposure” slider to “+1EV”. Then, in your Filmic preset, you should set your white and black points to be:
WhitePoint = 4 + 0.8 * ( +1EV )
BlackPoint = -8 + 0.5 * ( +1EV )

This is almost the general rule that filmic applies to set the white and black point by default. That seems to be:

WhitePoint = 4 + 0.8 * ExpCompensation
BlackPoint = -8 + 0.5 * ExpCompensation

where ExpCompensation is the exposure compensation applied by the exposure module consisting of a constant 0.5 boost and the negative of the exposure compensation that was set in the camera.

Here are some effects of this

• We are using an input range of about 12 EV which is comparable to the theoretical 11.7 EV of sRGB. So filmic is not doing HDR-tone-mapping by default.
• What the camera thought ought be middle gray will be 0.5 EV brighter in filmic. (Why is there this offset?)
• The filmic white and black points will be shifted towards the range of intensities that is properly exposed in the raw file.

I can see the wisdom of this rule for the window example of @kofa (or “ETTL”): since we underexposed the image deliberately, there must be some interesting detail in the highlights that we would like to preserve (the bright window). In order to properly tone map this image, we will want a white point that is relatively farther away from middle gray and this is equivalent to using low paper “hardness”.

However, the same default rule does not seem to make that much sense for ETTR (which is its main advertised use). There, it translates to using a hard “paper” that will help to discern detail in the shadows. However, already at +0.7 EV dialed in the camera, filmic’s default curve becomes non-monotonic (orange lower part) and thus anomalous.

• What are some good general rules for setting the white and black point? In general, will one tend to stick with the 2:1 ratio of white point to black point as in the default, or perhaps more with a 1:1 ratio like in the auto filmic style of @anon41087856?
• I know that filmic is not supposed to be automatic, but for sure it would be possible to create an auto mode for filmic that better matches expectations for a default usable result. Filmic would stilll allow the same artistic expression, but it would be easier to process huge batches of boring pictures.