Digital BW, The Print

> I still don't understand.  Why can't you get the exact same effect in PS
on
> a file that is grayscale?  All a filter does is shift/modify the tonality,
> and you can easily do that in PS to a grayscale file.

It's not the same thing. Shoot a Macbeth colour chart in both colour and
B&W. When you scan the colour image in colour, and use the channel mixer in
PS to convert to greyscale, you can alter the translation of tonal
relationships between the colours, much as you can do with colour filters
when shooting B&W film. As the channel mixer is adjusted, the grayscale
portion of the Macbeth chart doesn't change much, whereas the tonal
placement of colour patches can be drastically changed.