Digital BW, The Print

ferdinand_paris wrote:

> The print from a RGB monochrome image was the lightest, and exactly
> matched the black channel in a CYMK version of the RGB image.  A print
> from a grayscale version was darker but still not dark enough, and
> again matched the black channel in a CYMK version of the grayscale
> image.
> 
> I don't know what the Epson printer driver is actually doing, but it
> looks like it is taking each image, converting it to grayscale, and
> print *only* the black channel.  I thought BO was supposed to print
> *all* the channels using the black cartridge.

Black Only printing will only use the black channel, head, ink. A 
greyscale file will most likely be kept as a greyscale file in 
the Epson driver's BO mode when the last computes the data that 
has to go to the black head.  The original information should be 
rasterised to greyscale for the black channel only whether it is 
a greyscale, greyscale RGB or greyscale CMYK file.  Some drivers 
do not have a real BO output, all the color channels are used 
instead and a composite grey is printed. That's like printing 
greyscale images in colour mode, the neutrality depends on the 
consistency of the printer and/or its profiling.

There's no way you will get a separate "black plate" "black 
generation" printing from an Epson driver other than by printing 
in color mode and either the color carts are empty or the color 
heads kaputt (or both:-).  The Epson driver is an RGB type that 
will always do a hidden RGB>CMYK conversion (in color mode) on 
any file that will be printed in color mode, even on a CMYK file. 
The last will first be converted to RGB and then again to CMYK 
internally. No chance to interfere there. So what may look like a 
black channel print must be something else or your color carts 
are empty.

I think you are actually printing BO but there's a gamma shift in 
the workflow somewhere. That's why I suggested to check the 
embedded profile influence and switching to sRGB to see what 
changes.

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla

 >> The other choice is BO printing only which is
 >> using the K channel only from 0-100%. Some Epsons don't have 
that
 >> last choice in practice.


 >I'd hardly call it a choice.  No selection of channels or 
percentages

That's why it is called an "RGB" driver, unlike a good RIP you 
can't influence the conversion to CMYK, profiling is done at RGB 
level and linearisation, ink limitation, black generation is in a 
black box internally. The paper settings you can select in the 
printer menu will have different values for the ink limits etc 
(at least in color mode) but they are not transparant either and 
the differences not that high. But it helps sometimes to get a 
bit more black with the right paper setting.

Archive that driver if I'm wrong, it could become a collecter's 
item one day :-)

Ernst