Datacolor User to User Support Group.

I'm getting a very light 21 step grayscale after using Tools:Measure.
 I'm creating curves for Gold Fibre Silk using the QTR curves for
Silver Rag.  After clearing the Silver Rag values for, say, the cool
curve I print a 21 step grayscale without any values I then follow the
steps David outlined, measure and get the LINEARIZE="..." text file. 
I paste it to the QTR Linearization Values tab and create the curve. 
When I then print another 21 step grayscale using one of the created
curves it's way too light.  I calibrated the spectro using paper white
and not the tile.

What are the values the spectro produces?  The numbers I get range
from 2.07 down to 0.11.  The linearization values that come with QTR
for Silver Rag, for instance, range from 97.38 down to 5.16.  Are we
talking apples and apples here or is one Lab and the other density?

Thanks for any help.

Tom Husband
S3P 3.0

Tom

For the work we are doing, numbers in the range of 100 to 10(+or-) are LAB
L* values. Numbers in the range of .1 to 2.4 (also +or-) are visual density
values. Either values can be used for QTR linearization.

I know David Tobie suggested you calibrate using the paper. I'm not sure why
he recommended that. It could be that the paper you are using has
fluorescent OBAs that throw off the spectro and calibrating that way might
help in compensating for that situation.

You can convert between L* and density. There is Bruce Lindbloom's
companding calculator at:
		http://www.brucelindbloom.com/index.html

or you can use the curveEvalV2.xls spreadsheet I uploaded to the QTR mail
list web pages at:
		http://tech.groups.yahoo.com/group/QuadtoneRIP/files/Tools/

Using Bruce Lindbloom's calculator you can see that your values correspond
as follows
	Density 2.07   ==		L* 7.69
	Density 0.11   ==       L* 90.6

To me that value for paper white seems too dark. In fact, if I calibrate
normally and measure one of my papers I get a L* for paper white of 96.3. If
I calibrate using the paper and then measure the paper I get a L* for paper
white of 90.3. Calibrating with the paper doesn't make sense to me.

Hope this helps

Tom Moore

> -----Original Message-----
> From: colorvision_group@yahoogroups.com
> [mailto:colorvision_group@yahoogroups.com] On Behalf Of Tom Husband
> Sent: Thursday, February 07, 2008 10:49 PM
> To: colorvision_group@yahoogroups.com
> Subject: [colorvision_group] QTR Linearization Values
> 
> I'm getting a very light 21 step grayscale after using Tools:Measure.
>  I'm creating curves for Gold Fibre Silk using the QTR curves for
> Silver Rag.  After clearing the Silver Rag values for, say, the cool
> curve I print a 21 step grayscale without any values I then follow the
> steps David outlined, measure and get the LINEARIZE="..." text file.
> I paste it to the QTR Linearization Values tab and create the curve.
> When I then print another 21 step grayscale using one of the created
> curves it's way too light.  I calibrated the spectro using paper white
> and not the tile.
> 
> What are the values the spectro produces?  The numbers I get range
> from 2.07 down to 0.11.  The linearization values that come with QTR
> for Silver Rag, for instance, range from 97.38 down to 5.16.  Are we
> talking apples and apples here or is one Lab and the other density?
> 
> Thanks for any help.
> 
> Tom Husband
> S3P 3.0
> 
> 
> 
> 
> Yahoo! Groups Links
> 
> 
>

Thanks Tom for all the information.  I'll play around some more this
weekend.  Maybe I'll pull out the old X-Rite 810 and see what it says.
 I really want to use the spectro, however, as it streamlines the process.

Thanks David, I'll try measuring Lab rather than density although QTR
should be able to use either I believe.

Again, I appreciate your help.

Tom Husband
--- In colorvision_group@yahoogroups.com, CDTobie@... wrote:
>
> 
> In a message dated 2/7/08 10:49:19 PM, tom.husband@... writes:
> 
> 
> > What are the values the spectro produces?  The numbers I get range
> > from 2.07 down to 0.11.  The linearization values that come with QTR
> > for Silver Rag, for instance, range from 97.38 down to 5.16.  Are we
> > talking apples and apples here or is one Lab and the other density?
> > 
> 
> 97   to 5 would be L*a*b*, 2 to .1 would be visual density (or the
way you 
> did it, relative density). Definately a mismatch. Go back, calibrate
on the 
> white tile, and export Lab values, if thats what the QTR values use...
> 
> C. David Tobie
> International Product Technology Manager
> Digital Imaging & Home Theater
> Datacolor Inc.
> CDTobie@...
> www.datacolor.com/spyder3
> 
> 
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