Thanks, DrDre! This is great stuff! Your results are excellent but, more important, the process subdues “personal perception” twiddling … to move the faded film back to specs (all things considered).
I suspect that other functions in my paint program (gamma, mid-tones, etc.) are wrong (that is, made for different purpose) but serviceable in proof-of-concepts. On this laptop, it appears my last picture “inexplicably” went bluish in the dark shadows of a “neutral color” bunker after application of “mid-tones” (contrast).
Are such “standard” functions in your process pipeline? Or would generalized functions, created to be more spectrum symmetrical, be more suited to this task? (I was thinking of testing such.)
For the color restoration algorithm I use mainly custom built functions, based on internal MATLAB functions for interpolation, and curve fitting. The function actually only contains about 50 lines of code.