Digital BW, The Print

evanj1969 wrote:
> 
> when building curves in Photoshop for UT2/UT7 etc.. everyone seems to 
> be working RGB vs. CMYK.
> does RGB have an advantage over CMYK (excluding file size)?
> 
> would it not make more sense to control each color jet with its 
> corresponding channel in Photoshop???
> 
> i've always work in RGB, but is it better/easier?
> 
> anyone have thoughts or experience using each for the same thing?

The Epson driver knows only RGB as the input format. When you 
deliver CMYK (in any fashion) to the driver it will first 
convert it to RGB and after that apply its own CMYK conversion 
again. So there's no advantage to use the CMYK descriptions 
for B&W quad sets if you are using the Epson driver. There's 
even less transparency in what happens to the data through all 
the conversions when using CMYK curves in PS. That's also true 
for color printing with the Epson driver.

It would be nice to control each color jet (C-M-Y-K or 
C-c-M-m-Y-K(-k)) but even some commercial RIPs do not allow 
that: the "RGB" ones are like the Epson driver but there are 
also RIPs around that only use CMYK channels so the 6-7 
printers do not get a true 6-7 channel control. The special 
B&W RIPs now around are actually controlling the individual 
channels but you can't consider that to be CMYK curves either, 
they are grey + toner curves in a sense. K generation isn't a 
result of CMY amount in those curves.

I'm using a Wasatch SoftRip and have to use a kind of CMYK 
curves to get an Epson 9000 with UT in control. But I apply 
them in the RIP calibration software, the RIP gets a kind of 
greyscale images as input and the conversion is done with 
weird CMYK curves, K generation is taken out by other means

Ernst