Digital BW, The Print

> Going through the last print exchange (I'm not rubbing this in but am
> studying it) - I noticed that several used the channel mixer to
> convert to greyscale.
> 
> Could a few people comment on why they might use the channel mixer
> vs. Image/Greyscale (dump color info) &/or simply desaturate?

Control. 

When you use CHMX you control the blend ratio of the RGB channels. If your
original started out as color film this gives you a huge amount of tonal
control, less so if your original was BW. (In both cases a color scan is a
given however).

Image/grayscale is based on a blend of roughly 60% RED/ 29% Green/ 11% Blue.
Channel mixer allows you to choose your blend ration.

I'm not sure what desaturate is based on, but I'd guess it's the Luminosity
channel from LAB.

If it's not than that makes a fourth option. Additionally you could take any
single RGB or CMYK channel too, as another option.

Bottom line is that the other options just give you what they give you while
CHMX allows *you* to play with it. They're all viable options, and which
gives the best result may vary from one image to another.

If you have the interest to get into a channel by channel understanding of
PS I recommend Professional Photoshop 6, by Dan Margulis. Expect to read it
a couple of times. It ain't for the faint of heart, but it really gets into
the architecture of a digital image.

Todd