I have a Nikon D90 DLSR and and from time to time I want to convert color photographs these into B&W photos. I use the open-source and completely free GIMP to edit the pictures and do B&W conversion.
Using the built-in grey scale conversion often doesn’t come out to nicely, so I was wondering how to emulated the classic B&W films using the channel mixer in GIMP. I turns out that Petteri Sulonen on his blog www.prime-junta.net had done just that. On the left I am showing the Channel Mixer window in Gimp to converting a color photography using the Ilford XP2 Super channel settings. Below is list of his findings (I have done this mainly to have a online copy in case his blog goes offline).
My only small contribution is a ZIP file with all the profiles saved as GIMP channel mixer settings files, so the profiles can easily be loadd: GIMP-BW-film-Channel-Mixer.zip 6KB.
|Ilford Delta 100||21||42||39|
|Ilford Delta 400||22||42||37|
|Ilford Delta 400pro||31||36||33|
|Ilford XP2 Super||21||42||37|
|Kodak Tmax 100||24||37||39|
|Kodak Tmax 400||27||36||37|
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hm .. I hope you know that, when doing B/W photography, one usually uses the highest available ASA aka ISO film. Back in 2002/2003, when I still did that excessively, I used at least ASA 400 films, most times 800s thou.
Anything below ASA 200 is just good for simple holiday pictures.
For one I haven’t discussed film speeds or their digital equivalents in this post and secondly I think you have misunderstood the concept of film speeds.
The more light sensitive the film the higher the ISO number and the light sensitivity is related to the size of the grains in on the film. So, if I wanted a very sharp photo without grains in a well-lit setup I would choose a low ISO number film, such as 100 or 200. If I on the other hand need a faster film in a badly lit environment and didn’t mind the increased graininess I would choose a higher ISO number such as 400, 800 or even higher. See the wikipedia article on film speed if you need more info:
So in summary I use the lowest ISO number possible in a given situation to achieve the least grainy/noisy picture I can get. If I later want more grains I can add the digitally.