Fascinating! Ho do you subtract the two DNG? Is that in your R code?
Sure, all code is available for the four exercises (there is a link to the repo in the end of each article). The RAW subtraction is as simple as:
# LINEAR SUBTRACTION
imag=img[[1]]-img[[2]] # (Ambiente + Artificial) - Ambiente
imag[imag<0]=0 # clip negative subtractions
An animated GIF showing the before/after colour temperature matching:
Regards