Digital BW, The Print

> I worry about it, too.  There is a very widespread but 
> mistaken belief that the images produced by any B&W film can 
> be duplicated by some magic manipulation of a color image in 
> Photoshop.

There are other problems with this approach as well. If you use the
channel mixer and make large adjustments in the relationships between
colors you often end up with grainy images, loss of detail and halos
around objects in the transition areas between colors.

Here's an example:
http://daniel.staver.no/img/channelmixer1.jpg

The picture is a high quality jpeg from a Minolta Dimage 7i (which I
sold again last year in favor of my old analogue cameras btw).

Picture 1: Here I've used channel mixer to tone down the blue and
brighten red. I like contrasty images, so for me this is a look I'd
often like in my pictures.

Picture 2: Here I've made a mask of the flower (a really poor mask, but
it's just an example), converted to grayscale and applied curve
adjustment to the image with the mask in place to simulate adjustments
similar to what I did with the channel mixer. 

Picture 3: The original image. 

The result in the second image is much better than the first since
detail from all three channels is combined, and adjustments are then
made while the channel mixer simply discards information from channels
you don't use which results in exaggerated grain and loss of detail.

I notice the same effects on 16bit scans I make with my FS4000 and then
convert to BW using channel mixer, so the problem is not limited to
JPEG's from digital cameras.

So all technicalities aside, these problems have made me wary of doing
big tonal adjustments with the channel mixer, and I've mostly switched
from trying to make good BW from color film and now try to make it right
with BW film and filters when I record the image instead.

--
Daniel Staver
http://daniel.staver.no