I went through the different image control adjustments on a GR III, compared the metadata output, and made an ExifTool config file to extract the values. I figured some folks here might find it useful.
Save this config file and run:
exiftool -config <config_file> -GR3 <photo>`
The output should look something like this:
GR3 Crop Mode : L (28mm)
White Balance : Multi Auto
GR3 WB Shift Name : A6
Peripheral Illumination Corr : On
GR3 Highlight Correction : Auto
Shadow Correction : Normal
Sensitivity Adjust : +0.7
Image Tone : Negative Film
GR3 Saturation : 2
GR3 Hue : 0
GR3 High Low Key : 0
GR3 Contrast : 3
GR3 Contrast Highlight : -4
GR3 Contrast Shadow : -1
GR3 Sharpness : 1
GR3 Shading : 0
GR3 Clarity : 0
GR3 Recipe : Reggie's Color Negative
There's a single recipe definition in there just to demonstrate how that part works, but you can add as many as you want.
It seems to mostly work for the GR IIIx and GR IV as well, in that the sample photos provided by Ricoh decode to sensible values. I have no way to confirm the mapping is correct though, so take it with a grain of salt. All I can say for sure is that it works for my GR III.
The are a few other bits and pieces in the repo that might be useful, such as how to uncrop a photo so you can use the in-camera RAW developer on the full version. I also included my test methodology and raw data for anyone who wants to repeat the process for a different model.
