QTR-Quadtone RIP

Howard

I plotted your density values to have a look and the values are fairly
linear (i.e. they are fairly far from the LAB curve). One thing you might
try is to increase the gamma value of the gray curve. I'm not sure if you've
changed it yet, but assuming it's at its default value of 1, you could try
something in the 1.5 to 2 range. That would bring the curve closer to the
target LAB values before linearizing and might make it easier for the
linearizer to work its magic.

I'm not sure what others do, but I go through several iterations for each
curve adjusting the highlight, shadow and gamma values to bring the curve as
close as I can (reasonably close anyway) to LAB, before linearizing. The
curveeval spreadsheet I posted makes it convenient to save and plot curves
over several iterations and gives you a sense for the effect of changing
values. It's set up for the 21 step wedge, but that's a lot more convenient
to use until you get the curve close anyway.

At some point early on with QTR Roy told me that it was better to bring the
curve closer to the target profile using the shadow and highlight (and gamma
if necessary). This way the linearization would be a small adjustment of the
curve rather than a major move. I've not seen much discussion of this
recently, but I still do it out of habit. It's fairly quick once you get a
feel for what the numbers do. The main thing to remember is that larger
numbers make the density curve lower. That's true for all three values,
although the gamma changes have larger effect.

Tom Moore

> -----Original Message-----
> From: QuadtoneRIP@yahoogroups.com [mailto:QuadtoneRIP@yahoogroups.com] On
> Behalf Of Howard Shaw
> Sent: Friday, October 28, 2005 12:12 PM
> To: QuadtoneRIP@yahoogroups.com
> Subject: Re: [QuadtoneRIP] Error message: Invalid linearize curve - not
> constantly increasing
> 
> I have ink limit at 90%, boost at 95%, shadow at 12 & overlap at 16. The
> paper is Permajet Alpha. The limit is quite high so I'm not sure how
> much effect black boost is having anyway. I chose the high limit as the
> dmax was at its greatest (1.72 absolute) on the 90% patch.
> 
> I'm using x-rite 810 for measurements and I've re-checked them and they
> are consistent.
> 
> I'll have a play around with reducing the boost & the overlap as I don't
> seem to get quite the dmax I did on the calibration strip.
> 
> Howard
> 
> 
> 
> 
> 
> John Moody wrote:
> > The last step has a much higher density increase than all others,
> > effectively asking the linearization to fix a sharp bend at the end of
> > the curve.
> >
> > Do you have black boost at a fairly high level?  If so, you may get
> > smoother results cutting back on black-boost, and upping the ink limit
> > to achieve the 1.69 Dmax you are getting.  A high shadow value can bend
> > the curve like that as well, but since it's only the last step, I'm
> > guessing black boost.
> >
> > Also, if you scanned the patches with an i1, you might go back and
> > re-read the last several in patch mode to see that you get consistent
> > values.  I have a hypothesis that the dark patch accuracy degrades with
> > increasing scan speed, but I have not seen others corroborate that.
> >
> >
> >
> > Best regards,
> >
> > John Moody
> >
> >
> >
> > -----Original Message-----
> > *From:* QuadtoneRIP@yahoogroups.com
> > [mailto:QuadtoneRIP@yahoogroups.com]*On Behalf Of *Howard Shaw
> > *Sent:* Thursday, October 27, 2005 5:51 PM
> > *To:* QuadtoneRIP@yahoogroups.com
> > *Subject:* [QuadtoneRIP] Error message: Invalid linearize curve - not
> > constantly increasing
> >
> >
> >
> > I was making a linearisation today with the following values from a
> > 51-step and got the above error message and the curve was not created:
> > 0.06
> > 0.08
> > 0.1
> > 0.12
> > 0.15
> > 0.17
> > 0.2
> > 0.23
> > 0.26
> > 0.29
> > 0.33
> > 0.36
> > 0.41
> > 0.45
> > 0.48
> > 0.53
> > 0.57
> > 0.61
> > 0.65
> > 0.69
> > 0.72
> > 0.75
> > 0.79
> > 0.83
> > 0.87
> > 0.91
> > 0.95
> > 0.98
> > 1.01
> > 1.04
> > 1.09
> > 1.12
> > 1.14
> > 1.18
> > 1.19
> > 1.22
> > 1.24
> > 1.28
> > 1.31
> > 1.34
> > 1.37
> > 1.4
> > 1.42
> > 1.46
> > 1.49
> > 1.52
> > 1.55
> > 1.57
> > 1.6
> > 1.62
> > 1.69
> >
> > All the values are increasing albeit not "constantly". If I change the
> > penultimate value from 1.62 to 1.63 the curve creation works. Any reason
> > this should be so?
> >
> > Howard
> >
> >
> >
> >
> >
> >
> >
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