Datacolor User to User Support Group.

I'm not sure what those exact numbers mean, because they will depend
on what light the film has been shot in - and of course they would
also be changed by the use of filters. However, there is an
interesting feature: for Ilford and Agfa films, the B number is lower
than the G number. For Kodak films it is the other way round. 

Why is this? Maybe it is because the mixer settings have been
estimated from the published spectral response curves. Agfa and Ilford
published wedge spectrograms made in tungsten light (2850 K for
Ilford), at one density only. Kodak publish equal energy response
curves at two densities. This makes Kodak films look as if the blue
response is higher than the green response, and vice-versa for Ilford
and Agfa. It's just the way the spectral sensitivity is shown. You
need to compare wedge spectrograms or equal energy curves. You can't
compare one with the other - that is misleading, and whoever wrote
those channel mixer numbers appears to have been misled. Not that it
matters one bit for imitating B&W film digitally, but it does matter
if you wish to understand the differences between real B&W films.

Best,
Helen

 

--- In colorvision_group@yahoogroups.com, "John Vitollo" <jvlist@...>
wrote:

> Johnny,
> 
> I just uploaded to the File section a PDF titled:
> 
> Photoshop_Channel_Mixer_Settings_B_W.pdf 
> 
> The PDF has Cannel Mixer values that replicate many popular B&W film
responses.
> 
> Best,
> 
> John V.
>