The only reason I enter this discussion is to raise caution in computer conversion to gray scale analysis (and have written a book covering this).
Color computer images are represented as Red, Green, Blue values generally in the range 0-255.
Grayscale images are represented as a single value (usually 0-255) as well.
A basic conversion from color to grayscale is to do something like (with some oversimplification here):
G = x*R + y*G + z*B
where x+y+z <= 1 (And in most common conversions x, y and y are not the same.
A Color to Grayscale conversion depends upon a relative weighting of the three colors in the conversion. And different conversion methods weight the colors differently. A tool like Photoshop has multiple such conversions available.
Likewise various films and even batches of the same type of monochrome film respond to red, green, and blue differently.
Furthermore, each grayscale color corresponds to a range of colors.
This kind of analysis can give pointers but it is not conclusive.