Digital BW, The Print

>... my R1800 sample is one of the few that would
> benefit from a 4th channel.
> 
> How would one go about using a 4th channel?

I think there is at least one list member who might have made some 4-
MK curves.  Unfortunately, no longer have the ones I experimented 
with.

I'd first see if there are channels that print smoother than others 
by putting the carts in different locations and printing 21-step test 
strips with each of the channels independent of the others.  It may 
be that you'll find there are some that are quite good and, when they 
are used as the 3 channels, are enough.

After finding the best 3, if there is still microbanding, I'd focus 
on where it is in the 21-step test prints and start the fourth MK a 
little before that, reducing the other three from that point on by 
1/3 the amount of the new channel's values.  This will have to be 
polished and linearized, but I think this basic approach will get you 
there.

Hope this helps.

Paul
www.PaulRoark.com