Opening an image I was sure didn’t have clipping, I was surprised to see the clipping indicator (set to 255) displaying. The raw histogram confirmed there was no clipping of the raw data. So what caused the clipping? There followed a process of turning off every single module possible to find the culprit. It was an educational exercise, helping me understand more about what effected the histogram. It also raised a few questions.
The closest match I could get to the raw histogram came with everything either turned off or set to ‘none’, except demosaicing, working space and output space (the latter two of which can’t be turned off). This surprised me, as I thought raw histogram represented data pre-demosaic, so why would setting demosaic to ‘none’ be less accurate than setting it to anything else?
Rawpedia says, “…the working profile will only specify the red, green and blue primaries, gamma will not change as RawTherapee’s processing pipeline is floating point with no gamma encoding (that is gamma = 1.0).” Yet when I change Tone Response Curve from ‘none’ to ‘custom’ and set gamma = 1, the results vary - the image gets much darker. It behaved this way with every working space tested. If Rawtherapee always uses a gamma of 1, why does changing the TRC in working profile to gamma = 1 give a different result?
I set profile back to neutral. Given the raw data wasn’t clipping, it was easy to retain the ‘clipped’ highlights in a variety of ways. Either by a) Reducing exposure, b) Lowering white point of exposure tone curve, or c) Lowering raw white point. As a starting point, are all these methods as technically valid as each other, or is their one superior/inferior option? Further, as someone accustomed to the scene-linear workflow in darktable, am I better off bringing those highlights back with dynamic range compression, similar to how I would use filmic? (In other words, set exposure for the midtones, and not worry about the highlights?)