I’m assuming that the colors in a scene-referred interpolated raw file (no “make it pretty” algorithms) are as close to the actual scene colors as most of us can get given that when we take pictures we don’t also measure scene colors using specialized equipment.
If the colors in the scene-referred interpolated image file are taken as the “not messed up” colors, then the degree that post-processing produces “messed up colors” can be quantified given suitable metrics. I used two metrics:
- How many degrees did the LCh hue change?
- By what percent did the LCh “Saturation” change?
For the above metrics, LCh “Saturation” is defined as the ratio of Chroma to Lightness, per Mark Fairchild, page 25 - as Fairchild notes, the Lab color space doesn’t have an officially sanctioned measure of Saturation:
Here are screenshots showing results of processing a sample raw file several different ways using darktable. The sample raw file was posted at the top of a “play raw” thread: [PlayRaw] Departing Storm - please note that in the screenshots below in this current thread I used a better white balance than I did for the files I posted in the “play raw” thread.
To measure “how messed up” colors might be as a result of using various darktable algorithms to make the image “pretty”, I pulled the darktable output into GIMP and placed four sample points, one each as follows:
- Blue sky
- Orange/brown field behind utility building
- Grass in front of utility building
- Dark area in the clouds
Above: scene-referred (no “make it pretty” processing) - these colors will be considered “base line” and “not messed up at all” other than the Lightness value being too dark in order to not have any clipped highlights.
Above: Scene-referred + base curve to stretch midtones and compress highlights (no toe to compress the shadows)
Above: Scene-referred + Exposure +Unbreak profile (tone curve module not yet applied), following this tutorial: Solving dynamic range problems in a linear way
Above: Scene-referred + Exposure + Unbreak profile + Tone Curve with automatic RGB to restore chroma, following this tutorial: Solving dynamic range problems in a linear way
Above: Scene-referred + Exposure + filmic, following this tutorial: https://github.com/darktable-org/darktable/pull/1811
OK, I’m going to hit the “Create Topic” button and then add the metric calculations in a separate post.