OK, the curves calculated were wrong because additionally to the exposure settings, the images used to calculate the curves had tonal curves applied (even if I asked the users to set everything to 0). I now repeated the exercise with the 'Linear' checkbox of DPP activated (this seems produce a gamma=1 output, which is irrelevant to calculate the curves, just will change their slope, but also ensures 0 processing).
The new curves show now that DPP's Exposure Control is a genuine exposure control
, performing on RAW levels the same linear scaling a change in exposure in the camera (aperture/shutter) would have produced:
(ignore the end part of the -1EV curve, your images simply didn't have data to calculate the curves there)
I found very strange that DPP's didn't have a proper exposure adjustment, it's a basic
tool (and besides the easiest to implement in the code, just need to multiply levels by a constant factor: 2.0 for the +1EV, and 0.5 for the -1EV). If using a linear profile, the same is achieved in PS with: