QTR-Quadtone RIP

--- In QuadtoneRIP@yahoogroups.com, "Tom Moore" <r.t.moore@r...> wrote:
> Jamie
> 
> I see you have xrite's toolcrib and a densitometer. What I do, is
print a
> step wedge (I use the 21 step), and then measure the density of each
step.
> Using toolcrib, I pop the density readings into an excel spreadsheet
that
> displays the densities as a graph. I can see how the density of each
step
> increases over the 0% to 100% black range. It should be uniformly
increasing
> over the range (i.e. it should not decrease). I usually end up
printing the
> stepwedge several times as I adjust the Highlight, Shadow, and Gamma
> parameters to bring the density curve nearer to linear. My
spreadsheet is
> set up to store and plot the density values from a number of runs as I
> (hopefully) get closer to my final curve. Plotting several
stepwedges lets
> you see the effect of changing the parameters.
> 
> The spreadsheet also can compute L* values from density so I can use
Roy's
> utility to create an ICC profile of the final curve for previewing in
> Photoshop.
> 
> Tom Moore

Hi Tom

What is the formula to convert dMax to *L? -or- can you share the
spreadsheet.

Also, does anyone know if there is an "Ideal Densities for Various
DMax" chart available that goes as los as dMax 140. I have some not so
great matte paper that maxes out at 142 on my UC 7600.

Thanks!!
tim

Tim

I see John Moody has provided the formulas you're looking for. My
implementation is different (mines a VBA function that can be used in a
spreadsheet) but both implementations give the same result to 14 decimal
places, except for the discontinuity area when we agree to "only" five
decimal points :-).

I updated my spreadsheet to include LAB density curves down for dmax down to
1.35. If you want a copy rather than making your own, email me and I'll send
it back.

Tom

> -----Original Message-----
> From: QuadtoneRIP@yahoogroups.com [mailto:QuadtoneRIP@yahoogroups.com] On
> Behalf Of timlbatten
> Sent: Monday, August 29, 2005 3:08 PM
> To: QuadtoneRIP@yahoogroups.com
> Subject: [QuadtoneRIP] Re: Curve building?/Spreadsheet
> 
> --- In QuadtoneRIP@yahoogroups.com, "Tom Moore" <r.t.moore@r...> wrote:
> > Jamie
> >
> > I see you have xrite's toolcrib and a densitometer. What I do, is
> print a
> > step wedge (I use the 21 step), and then measure the density of each
> step.
> > Using toolcrib, I pop the density readings into an excel spreadsheet
> that
> > displays the densities as a graph. I can see how the density of each
> step
> > increases over the 0% to 100% black range. It should be uniformly
> increasing
> > over the range (i.e. it should not decrease). I usually end up
> printing the
> > stepwedge several times as I adjust the Highlight, Shadow, and Gamma
> > parameters to bring the density curve nearer to linear. My
> spreadsheet is
> > set up to store and plot the density values from a number of runs as I
> > (hopefully) get closer to my final curve. Plotting several
> stepwedges lets
> > you see the effect of changing the parameters.
> >
> > The spreadsheet also can compute L* values from density so I can use
> Roy's
> > utility to create an ICC profile of the final curve for previewing in
> > Photoshop.
> >
> > Tom Moore
> 
> Hi Tom
> 
> What is the formula to convert dMax to *L? -or- can you share the
> spreadsheet.
> 
> Also, does anyone know if there is an "Ideal Densities for Various
> DMax" chart available that goes as los as dMax 140. I have some not so
> great matte paper that maxes out at 142 on my UC 7600.
> 
> Thanks!!
> tim
> 
> 
> 
> 
> 
> 
> Yahoo! Groups Links
> 
> 
> 
> 
>

Tom,
Thanks for taking the time to check the functions.  Good to know they're OK.
My ink comes tomorrow, so I'll be putting them back to use.

Best regards,
John Moody

-----Original Message-----
From: QuadtoneRIP@yahoogroups.com [mailto:QuadtoneRIP@yahoogroups.com]On
Behalf Of Tom Moore
Sent: Monday, August 29, 2005 5:40 PM
To: QuadtoneRIP@yahoogroups.com
Subject: RE: [QuadtoneRIP] Re: Curve building?/Spreadsheet

Tim

I see John Moody has provided the formulas you're looking for. My
implementation is different (mines a VBA function that can be used in a
spreadsheet) but both implementations give the same result to 14 decimal
places, except for the discontinuity area when we agree to "only" five
decimal points :-).

I updated my spreadsheet to include LAB density curves down for dmax down to
1.35. If you want a copy rather than making your own, email me and I'll send
it back.

Tom

Tom,

I wonder if you might consider uploading that Excel file to the Files 
section here instead?

I do not have a densitometer so I have to use my Epson 3200 scanner 
for my first attempts at curve creation I now have underway with the 
UT7 inkset. Being able to convert luminosities to densities would be 
very handy and although I could just use the formula from John's post 
I would bet I am not the only one in the 'no densitometer' boat.

Also Tom, while I have you on line so to speak :~) I wonder if you 
can clarify something from your user guide. In the Ink Density 
Calibration section on page 15 you say:

"For Ultrachrome inks, the measurements above are all that is 
required. For QuadTone inks, this process is repeated for each 
lighter ink, comparing it to the next darker ink, calculating its 
density relative to that ink and then converting it to a density 
relative to black."

I believe that what you mean to say is simply that the process is 
repeated for each lighter ink, calculating its density relative to 
black. Is that not correct? All that one needs later in the curve 
generation is the percentage of the black ink stepwedge that 
corresponds (in density terms) to 100% of the other gray inks, 
correct? If so, it seems to me you do not need to in any way compare 
the other grays with each other, but only with the black stepwedge 
densities directly. Thanks to confirm if I've understood things 
correctly here.

Best wishes,

Dave Meddings


--- In QuadtoneRIP@yahoogroups.com, "Tom Moore" <r.t.moore@r...> 
wrote:
 
> I updated my spreadsheet to include LAB density curves down for 
dmax down to
> 1.35. If you want a copy rather than making your own, email me and 
I'll send

> it back.
> 
> Tom

You can also go to Bruce Linkbloom's site and use the Companding Calculator to go back and 
forth.  http://www.brucelindbloom.com/

Angelo

> 
> Hi Tom
> 
> What is the formula to convert dMax to *L? -or- can you share the
> spreadsheet.
> 
> Also, does anyone know if there is an "Ideal Densities for Various
> DMax" chart available that goes as los as dMax 140. I have some not so
> great matte paper that maxes out at 142 on my UC 7600.
> 
> Thanks!!
> tim

Dave

The CurveEval Excel spreadsheet is in the files section now. Note that you
may have to enable macros, depending on your security level setting in
Excel. No macros enabled - no work.

See response below regarding your other question.

Tom

> -----Original Message-----
> From: QuadtoneRIP@yahoogroups.com [mailto:QuadtoneRIP@yahoogroups.com] On
> Behalf Of David Meddings
> Sent: Tuesday, August 30, 2005 4:16 AM
> To: QuadtoneRIP@yahoogroups.com
> Subject: [QuadtoneRIP] Re: Curve building?/Spreadsheet
> 
> Tom,
> 
> I wonder if you might consider uploading that Excel file to the Files
> section here instead?
> 
> I do not have a densitometer so I have to use my Epson 3200 scanner
> for my first attempts at curve creation I now have underway with the
> UT7 inkset. Being able to convert luminosities to densities would be
> very handy and although I could just use the formula from John's post
> I would bet I am not the only one in the 'no densitometer' boat.
> 
> Also Tom, while I have you on line so to speak :~) I wonder if you
> can clarify something from your user guide. In the Ink Density
> Calibration section on page 15 you say:
> 
> "For Ultrachrome inks, the measurements above are all that is
> required. For QuadTone inks, this process is repeated for each
> lighter ink, comparing it to the next darker ink, calculating its
> density relative to that ink and then converting it to a density
> relative to black."
> 
> I believe that what you mean to say is simply that the process is
> repeated for each lighter ink, calculating its density relative to
> black. Is that not correct? All that one needs later in the curve
> generation is the percentage of the black ink stepwedge that
> corresponds (in density terms) to 100% of the other gray inks,
> correct? If so, it seems to me you do not need to in any way compare
> the other grays with each other, but only with the black stepwedge
> densities directly. Thanks to confirm if I've understood things
> correctly here.
> 

What I stated, I think is correct. You could do what you're suggesting
(simply estimating each lighter inks density as a percentage of black) but
doing it in two stages I think is more accurate and not any more work.

Basically:
You compare LK with K. Suppose it's 40% of K.
Next you compare LLK with LK. Suppose its density is 40% of LK. Then its
density is 16% (40% of 40%) of K. The 16% is what you use in QTR. What I was
describing in my document was how you determine the number.

Doing the comparison with K could be done and probably wouldn't make too
much difference in the example I gave. When there are lots of gray inks
(e.g. the K7), the numbers would get pretty small and inaccuracies would
creep in. 


... snip...


Tom

Thanks!  The VBA function is much more elegant than an excel formula.
Let's hope that the list does not get hammered with too many duplicate
questions about the spreadsheet.

Best regards,
John Moody

-----Original Message-----
From: QuadtoneRIP@yahoogroups.com [mailto:QuadtoneRIP@yahoogroups.com]On
Behalf Of Tom Moore
Sent: Wednesday, August 31, 2005 12:47 AM
To: QuadtoneRIP@yahoogroups.com
Subject: RE: [QuadtoneRIP] Re: Curve building?/Spreadsheet

Dave

The CurveEval Excel spreadsheet is in the files section now. Note that you
may have to enable macros, depending on your security level setting in
Excel. No macros enabled - no work.

See response below regarding your other question.

Tom