OK, so we already saw how to make a black and white image out of a colour one using channel mixer in GIMP. We might select any proportion (even negative...) for each of the primary channels, Red, Green and Blue. This way, we can produce any interpretation of the original colour information.
Have you ever thought how it worked in "old" films? Silver halide salts (most commonly used chemical in B&W films) reacted in different ways to each light wave length (or colour...), depending on chemical composition and layering of the actual film. As a result, each brand and type of film had a
slightly different performance in similar light conditions. On the other side, panchromatic films were supposed to react in a similar way to all colours.
Left: Original - Center: Agfapan 100 - Right: Ilford Pan F
Independently from film grain (I might deal about this in a later post), the representation of colours in B&W film was quite personal, and most photographers ended up using a "preferred" film. Now, is it possible to reproduce that personal film "feeling" with image editors? Well, we can try...
Basically, what we will do is to use specific conversion values in the channel mixer, as a first approach. From the great Petteri blog page (http://www.prime-junta.net/pont/How_to/100_Curves_and_Films/_Curves_and_films.html), you can get, for example, the following proposals:
|Ilford Delta 100||21,42,37|
|Ilford Delta 400||22,42,36|
|Ilford Delta 400 Pro & 3200||31,36,33|
|Ilford Pan F||33,36,31|
|Ilford XP2 Super||21,42,37|
|Kodak Tmax 100||24,37,39|
|Kodak Tmax 400||27,36,37|
By using these values, you will obtain different results, depending on the selected "film setting". You might have not chosen these specific settings - but this is a fair approximation to what B&W films did...
Next: Film Simulation: 2 - Colour (Theory)