Quote Originally Posted by Kirk Gittings View Post
I just did the tests scans on an Epson 750, 16 bit Grayscale, Silverfast AI Studio, white, red, green and blue channels. The differences, though subtle, are the same I would expect from separating the channels from an RGB scan. Similar to Tyler's examples but a bit subtler with slightly better sharpness, shadow detail and less noise in the green chanel.
I conducted a similar test to compare.

Interesting, within Silverfast, I was/am able to "select" separate color filters for both RGB and Grayscale. However, for each RGB scan with a separate filter for white, red, green and blue--I just didn't see discernable differences. This leads me to wonder that while "selection" is possible--it may not be functionally operational in either Silverfast or may be the 4990 scanner. Hmmmmm!

Also, I compared 16 bit grayscale with filters (white, red, green, blue) and 48 bit scans with similar color separations in P'shop. With the 4990, there are subtle differences--the 48 bit scans with green channel isolation in P'shop generally appear better in terms of detail and noise.