QTR-Quadtone RIP

On another group I wrote a fair amount about the linearization, icc 
profiling, etc.
I'm not sure I addressed all you questions but I think it will help a 
lot.

See:
http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/message/68052

Roy

On Monday, September 26, 2005, at 04:23  PM, Eric Ashworth wrote:

> Hello all,
>
> I'm hoping some of the ubertechs on the list can help me out.  I have
> been working with QTR off and on for a couple months and thought I
> had a pretty good grasp on the process. However, I recently purchased
> a densitometer to create more accurate linearizations. This has
> resulted in some serious confusion for me. I had mentioned a couple
> weeks ago that I was going to post some of the curves I had
> generated, but have decided not to at least for now as I discovered I
> am entirely unsure of their accuracy. I've read everything I could
> get my hands on re: QTR including searches through past messages and
> have still not found the answers I'm looking for.
>
> Before working with the densitometer, I was using my scanner and
> eyeballing the final curves. This was resulting in quite excellent
> screen to print matching (with a few discrepancies, depending on the
> image) without any need for a custom dot gain profile or any of the
> other methods used for screen/print matching. In other words, I was
> able to print an image straight through QTR and get essentially what
> was on my screen.
>
> Now however, using the densitometer readings, aside from getting a
> smooth ramp, after linearizing and achieving near ideal densities (at
> least as far as what is listed in the available documentation) the
> images print quite dark when printed directly and require a PS
> adjustment layer to print properly. It seems to me that the curve
> needs to be lighter, but if I make it lighter then the densities will
> no longer match the ideal values.
>
>  From what I understand of the average color management workflow,
> there are essentially two steps in the process of managing a device,
> ie: calibration and profiling/characterization. Calibration is the
> process of modifying the devices behavior (linearizing the inks,
> aligning the printhead(s) etc.)  in order to bring it to a standard
> state and profiling is the process of recording its behavior after
> calibration, and creation of the profile with its LUTs for future
> conversions so that the color that is printed, is approximately what
> we see on our screens. If working with color inks, the profile is
> clearly necessary as the linearization of the inks does not
> necessarily result in the exact expected colors when the inks are 
> mixed.
>
> So, in the case of BW, I assumed that since we're working
> monochromatically, there wouldn't really be any need for profiling,
> as the linearization should result in the desired values. To be a
> little more specific, since the process of linearization is setting
> up the curves so that the printer produces specific densities when
> receiving cmyk values in a single ramp (as opposed to mixing multiple
> ramps for color mixing), the process of profiling the printer's
> output would only be redundant as the only purpose would be to
> profile the output of values since there isn't any color to consider
> (aside from the issue of being able to soft proof with the correct
> tonality).
>
> Since a color management system is meant to translate values as
> accurately as possible from one device to another via the PCS, I
> figured that what appeared to be 50% grey on my monitor would
> correlate to the corresponding ideal density for the 50% patch on the
> test print. But, this has not been the case each time I have redone
> the process.
>
> So in specific, I'm hoping someone could clarify the following,
>
> 1. If an ink/paper combination is properly linearized, should the
> output be reasonably close to what's on the screen if the display has
> been properly profiled? Or is it also necessary to profile the BW
> output or use one of the other screen/print matching processes to get
> this type of match?
>
> 2. What exactly would be the purpose of profiling BW output, aside
> from being able to soft proof for tonal variations?
>
> 3. Since QTR will either take an image converted to 2.2 gamma and
> print it without altering the values or in the case of images not
> saved in 2.2 gamma, will convert to 2.2 gamma prior to printing, ie:
> change the numbers to correlate to the previous color space,  what
> would be the purpose of using one color space over another since what
> is seen on screen and subsequently encoded in the 2.2 gamma space, is
> what is printed?
>
> 4. Are the ideal densities meant to correspond to our visual response
> to changes in value? I thought this was the case but now I'm not sure.
>
> 5. Although the curves are not profiles are they meant to be used as
> such, or are they more like the Epson driver settings that just
> control the ink limits etc. and should be used in conjunction with
> destination profiles?
>
> 6. Am I just way off base, regarding my understanding of this
> process, or am I headed in the right direction?
>
> By the way, I'm working on a mac with OS X, the beta version of QTR,
> using an X-Rite DTP-32 (have calibrated it at least once a week), and
> using a 1280 with a modified version of the UT2 inkset that replaces
> the sepia ink in the yellow position for the light, cool grey FSN-Y.
> I'm also using a 2200 with UC inks, an R200 with some experimental
> inks and a 7600 with the UT7 inkset, so I really want to know how to
> do this stuff right.
>
> Thanks in advance for any help or information.
>
> Eric
> www.ericashworth.net
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
-
Roy Harrington
roy@...
Black & White Photo Gallery
http://www.harrington.com