Digital BW, The Print

Greetings, group.

When trying to linearize for a particular printer/paper/ink 
combination, what is the best way to determine the Aims for each %K 
value? Is linearization supposed to be determined strictly 
mathematically or is there some element of perceptual linearization 
involved?

I believe most RIPs like StudioPrint, InkJet Control, and probably 
QTR (I haven't tried it yet) either have built-in Aims or simply 
allow you to enter your density measures and then calculates it 
automatically, but I'm curious about the algorithm(s) that are used 
to establish the linearization.

Thanks for any insight.
Peter.

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Peter" 
<spamme2001@m...> wrote:
> Greetings, group.
> 
> When trying to linearize for a particular printer/paper/ink 
> combination, what is the best way to determine the Aims for each %K 
> value? Is linearization supposed to be determined strictly 
> mathematically or is there some element of perceptual linearization 
> involved?
> 
> I believe most RIPs like StudioPrint, InkJet Control, and probably 
> QTR (I haven't tried it yet) either have built-in Aims or simply 
> allow you to enter your density measures and then calculates it 
> automatically, but I'm curious about the algorithm(s) that are used 
> to establish the linearization.
> 
> Thanks for any insight.
> Peter.

I can tell you that with QTR the linearization idea is to make
the Lab values linear -- i.e. a straightline.  The numbers are
entered as density but it's just a matter of conversion to Lab.

Roy

With StudioPrint at least, it's a two-step process. To grossly simplify, the function of 
linearization is to map a straight line of input to output (linear). Following that is a dot 
gain adjustment curve setting. This value chosen for this setting adds a non-linear 
gamma-type curve which is better suited to human perception, as we don't "see" in a 
linear fahion.

amadou diallo

Amadou Diallo wrote:

> With StudioPrint at least, it's a two-step process. To grossly simplify, the function of 
> linearization is to map a straight line of input to output (linear). Following that is a dot 
> gain adjustment curve setting. This value chosen for this setting adds a non-linear 
> gamma-type curve which is better suited to human perception, as we don't "see" in a 
> linear fahion.
> 
> amadou diallo

Amadou,

That extra step is only applied in B&W calibration I guess ?

Any data available of that gamma curve ?

When Roy uses Lab's linear greyscale isn't he getting the same 
necessary deviation from strict linearity ?  A perceptive greyscale.

Ernst

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla <E.Dinkla@c...> 
wrote:
> Amadou Diallo wrote:
> 
> > With StudioPrint at least, it's a two-step process. To grossly simplify, the function 
of 
> > linearization is to map a straight line of input to output (linear). Following that is 
a dot 
> > gain adjustment curve setting. This value chosen for this setting adds a non-
linear 
> > gamma-type curve which is better suited to human perception, as we don't "see" 
in a 
> > linear fahion.
> > 
> > amadou diallo
> 
> Amadou,
> 
> That extra step is only applied in B&W calibration I guess ?
> 
> Any data available of that gamma curve ?
> 
> When Roy uses Lab's linear greyscale isn't he getting the same 
> necessary deviation from strict linearity ?  A perceptive greyscale.
> 
> Ernst

Yes, Ernst.  A straight line in Lab produces a distinct upward
curve when measured in density units.

Roy

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla
<E.Dinkla@c...> wrote:
> Amadou Diallo wrote:
> 
> > With StudioPrint at least, it's a two-step process. To grossly
simplify, the function of 
> > linearization is to map a straight line of input to output
(linear). Following that is a dot 
> > gain adjustment curve setting. This value chosen for this setting
adds a non-linear 
> > gamma-type curve which is better suited to human perception, as we
don't "see" in a 
> > linear fahion.
> > 
> > amadou diallo
> 
> Amadou,
> 
> That extra step is only applied in B&W calibration I guess ?
> 
> Any data available of that gamma curve ?
> 
> When Roy uses Lab's linear greyscale isn't he getting the same 
> necessary deviation from strict linearity ?  A perceptive greyscale.
> 
> Ernst

Ernst, I'm not Amadou but I can reply to that. The last step is in any
mode, including the individual colors for CMYK, overall for quad mode.
It's a dot gain slider. Obviously 0 dot gain is extremely light by
anyone's standard. This entire issue has been a bit of a mystery for a
long time. What is perceptually linear? Is LAB? Probably much closer
than 0 dot gain. What percent dot gain corresponds to linear L values?
I've heard IJC has output gamma setting for the user to select.
Obviously StudioPrint leaves it up to the user to select.
I've put this issue before some pretty extreme geeks, and no
definitive answer came up. LAB has been suggested as a good "probable"
enough times to buy into. But I have yet to correspond a particular
dot gain selection in SP to linear LAB output and I wonder if one
found a setting that gave equivalent 50% density, if they would also
be equivalent throughout the rest of the scale. This is a little
outside my color geek range, so for now I've settled on 20%, and work
in a 20% dot gain space, so far so good. I'm curious what Amadou and
others are using.
Tyler

Tyler Boley wrote:

> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla
> <E.Dinkla@c...> wrote:
> 
>>Amadou Diallo wrote:
>>
>>
>>>With StudioPrint at least, it's a two-step process. To grossly
> 
> simplify, the function of 
> 
>>>linearization is to map a straight line of input to output
> 
> (linear). Following that is a dot 
> 
>>>gain adjustment curve setting. This value chosen for this setting
> 
> adds a non-linear 
> 
>>>gamma-type curve which is better suited to human perception, as we
> 
> don't "see" in a 
> 
>>>linear fahion.
>>>
>>>amadou diallo
>>
>>Amadou,
>>
>>That extra step is only applied in B&W calibration I guess ?
>>
>>Any data available of that gamma curve ?
>>
>>When Roy uses Lab's linear greyscale isn't he getting the same 
>>necessary deviation from strict linearity ?  A perceptive greyscale.
>>
>>Ernst
> 
> 
> Ernst, I'm not Amadou but I can reply to that. The last step is in any
> mode, including the individual colors for CMYK, overall for quad mode.
> It's a dot gain slider. Obviously 0 dot gain is extremely light by
> anyone's standard. This entire issue has been a bit of a mystery for a
> long time. What is perceptually linear? Is LAB? Probably much closer
> than 0 dot gain. What percent dot gain corresponds to linear L values?
> I've heard IJC has output gamma setting for the user to select.
> Obviously StudioPrint leaves it up to the user to select.
> I've put this issue before some pretty extreme geeks, and no
> definitive answer came up. LAB has been suggested as a good "probable"
> enough times to buy into. But I have yet to correspond a particular
> dot gain selection in SP to linear LAB output and I wonder if one
> found a setting that gave equivalent 50% density, if they would also
> be equivalent throughout the rest of the scale. This is a little
> outside my color geek range, so for now I've settled on 20%, and work
> in a 20% dot gain space, so far so good. I'm curious what Amadou and
> others are using.
> Tyler

Tyler,

I'm not a colour guru or geek either. On the Wasatch SoftRip that 
I have I can linearise and build a profile on top of that.
I assumed that the profile actually takes care of the human eye 
responsiveness to grey levels etc. As good as the color 
management works (see below). In absence of a ICC profile in quad 
profiling I can imagine a curve is needed that takes care of that 
human grey level response.

The Wasatch allows me to add correction curves on top of the 
linearisation curve for ink limitation etc.There is however no 
prebaked curve for quads added that should take care of the human 
factor. One improvises a curve that suits one's eyes.The Wasatch 
SoftRip isn't very B&W quad aware so that could be the reason but 
on the other hand I find it strange that StudioPrint (ICC 
profiled) has that option for colour as well. Is this not just 
the same correction facility for ink limitation etc but in this 
case the prebaked quad "human factor" curve has been added as an 
extra service?  Good service by Ergosoft then. But you shouldn't 
use that particular curve when it is for color printing that 
already relies on a custom ICC profile. That's my guess at least.

On thin ice now and in my own words.... Lab is "more or less" 
perceptually linear.  On top of that the approach by colour 
management applications isn't always in respect of the shape's 
construction. Gamut mapping for instance asks for a more 
complicated approach with (3d?) curved mapping (or tables) to get 
good perceptual hue matches. Most of the time it isn't done like 
that and shifts like the blue > purple hue occur. Similar problem 
with density dot gain.  Some polishing of the original 
mathematical setup of Lab is also needed apparently. All Bruce 
Lindbloom's territory. See the density dot maths at the bottom of 
this page:

http://www.brucelindbloom.com/index.html?UPLab.html

Ernst

Ernst Dinkla wrote:

>All Bruce 
> Lindbloom's territory. See the density dot maths at the bottom of 
> this page:
> 
> http://www.brucelindbloom.com/index.html?UPLab.html

Sorry, that doesn't work. Use
www.brucelindbloom.com/
then "calc" and then scroll downwards.

Ernst

Thank you to everyone who replied to my message -- this is exactly 
the discussion I was hoping for. 

For a variety of reasons I've decided that I'm not prepared for all 
the control a RIP will provide, but I'd still like the ability to 
tweak an existing profile to account for variances in paper batches 
or the unique characteristics of my printer, for example. About a 
year and a half ago I used the Curves Template located in the Files 
section 
(http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/files/Ima
ge%20Processing/) to create a Photoshop adjustment layer but I 
believe this spreadsheet does a strictly mathematical linearization.

I'm hoping to do something similar (i.e. measure the density values 
in a stepwedge, compare to some Aims and make an adjustment curve) 
but would like to account for perceptual issues. I'll see what I can 
figure out with the Bruce Lindbloom calculators.

Thanks again for your insight (and if you have any hints, I'm all 
ears!).

Peter.



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Peter" 
<spamme2001@m...> wrote:

> Is linearization supposed to be determined strictly 
> mathematically or is there some element of perceptual 
> linearization involved?

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla
<E.Dinkla@c...> wrote:
...
> The Wasatch allows me to add correction curves on top of the
> linearisation curve for ink limitation etc.

SP has a few places to set ink limits, before or after linearizing.
The final dot gain curve one can apply is at the very end of the
process after linearization has been done taking the limiting (new end
point) into account. My assumption is that it amounts to the same
thing in the end as the controls you have in the Wasatch.

> There is however no
> prebaked curve for quads added that should take care of the human
> factor. One improvises a curve that suits one's eyes.

That's what kind of bugs me, we do it to taste instead of an accepted
standard. We can both be linear, but be printing considerably lighter
or darker than each other depending on our eyes. Of course we are
editing our files to suit, but one would think there could be some
widely accepted standard that once we are all linearized to, the same
file would print similarly across the board.
Really outstanding single channel icc profiles would put much of this
to rest, if we both had them, we could print the same file
theoretically identically.

> The Wasatch
> SoftRip isn't very B&W quad aware so that could be the reason but
> on the other hand I find it strange that StudioPrint (ICC
> profiled) has that option for colour as well.

I'm not sure why one would need these controls for color, everyone
advises linearizing to 0 dot gain before color profiling. However this
raises some questions in my mind that would be more appropriate on
some other forums.

>Is this not just
> the same correction facility for ink limitation etc but in this
> case the prebaked quad "human factor" curve has been added as an
> extra service?  Good service by Ergosoft then. But you shouldn't
> use that particular curve when it is for color printing that
> already relies on a custom ICC profile. That's my guess at least.

Mine too.

> On thin ice now and in my own words.... Lab is "more or less"
> perceptually linear.

I'm showing my lack of formal color education here, but I think you
are right. I think LAB was developed over time to come as close as
possible to human visual perception.

>  On top of that the approach by colour
> management applications isn't always in respect of the shape's
> construction. Gamut mapping for instance asks for a more
> complicated approach with (3d?) curved mapping (or tables) to get
> good perceptual hue matches. Most of the time it isn't done like
> that and shifts like the blue > purple hue occur. Similar problem
> with density dot gain.  Some polishing of the original
> mathematical setup of Lab is also needed apparently. All Bruce
> Lindbloom's territory...

Lindbloom to the rescue again. I ran some tests, if we assume LAB is
perceptually uniform from gray values of 0,0,0 to 100,0,0, then middle
gray must be somewhere near 50,0,0. This means a dot gain of something
like 31+%, much more than I would have guessed. Some other tests in
photoshop confirm this. So I'm not sure if that helps at all.
I've come at this problem from every conceivable direction, including
density.
At this point I can only conclude that "linear" simply means that as
tones progress they do so in a mathematically consistent manner. Other
factors thrown in to make it perceptually desirable, like gamma or dot
gain, remain subjective decisions.
But that makes comparisons of systems based on those factors (it
prints too light, or too dark) useless, particularly if it can be
varied easily by the user but remain "linear".
Tyler

>This is a little
> outside my color geek range, so for now I've settled on 20%, and work
> in a 20% dot gain space, so far so good. I'm curious what Amadou and
> others are using.
> Tyler

Tyler,
I too use the 20% dot gain adjustment in StudioPrint (it's the default). Printing a stepwedge 
I can distinguish paper white from 2% ink and between 98% and 100% K. I have set up a PS 
grayscale working space of gamma 2.0. I find this gets me a good screen to print match. 
Of course you could go the other way and adjust dot gain in StudioPrint to match your PS 
gamma, but I was happy with the print contrast at 20% and so decided to bring the 
monitor in line.

amadou diallo

Ditto. It would be great if we could restrict the specification 
of "intent" to the contents of the digital file itself and be free 
to print with consistency on any number of devices. With the unique 
strengths and weaknesses of different printers, however, I wonder if 
this would ever be possible.

Peter.


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Tyler Boley" 
<tyler@t...> wrote:

> 
> That's what kind of bugs me, we do it to taste instead of an 
> accepted standard. We can both be linear, but be printing 
> considerably lighter or darker than each other depending on our 
> eyes. Of course we are editing our files to suit, but one would 
> think there could be some widely accepted standard that once we
> are all linearized to, the same file would print similarly 
> across the board.

Pretty unlikely to make it work across all the various systems people
are using here. But one would think at least amongst those that are
hardware linearized a high degree of visual similarity would result if
there were indeed some standard.
I can do it now between different papers, and different ink tint
combinations, assuming dmax is in the same ballpark amongst them.
Also, if we were both profiled with good gray profiles, if I assigned
my profile to an image, then you converted it to yours and printed
there, a decent match could be expected.
Tyler

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Peter"
<spamme2001@m...> wrote:

> Ditto. It would be great if we could restrict the specification 
> of "intent" to the contents of the digital file itself and be free 
> to print with consistency on any number of devices. With the unique 
> strengths and weaknesses of different printers, however, I wonder if 
> this would ever be possible.
> 
> Peter.
> 
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Tyler Boley" 
> <tyler@t...> wrote:
> > 
> > That's what kind of bugs me, we do it to taste instead of an 
> > accepted standard. We can both be linear, but be printing 
> > considerably lighter or darker than each other depending on our 
> > eyes. Of course we are editing our files to suit, but one would 
> > think there could be some widely accepted standard that once we
> > are all linearized to, the same file would print similarly 
> > across the board.

Happy with 20% here too, I just run into occassional problems with
files from other sources. Some untagged, some from people with bad
monitors, some with proofs printed on bad or unprofiled systems.
Have you tried the softproof method nailed down for the i1 by Roy and
Carl? Works quite well.
Tyler

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Amadou Diallo"
<amadiallo2001@y...> wrote:
> >This is a little
> > outside my color geek range, so for now I've settled on 20%, and work
> > in a 20% dot gain space, so far so good. I'm curious what Amadou and
> > others are using.
> > Tyler
> 
> Tyler,
> I too use the 20% dot gain adjustment in StudioPrint (it's the
default). Printing a stepwedge 
> I can distinguish paper white from 2% ink and between 98% and 100%
K. I have set up a PS 
> grayscale working space of gamma 2.0. I find this gets me a good
screen to print match. 
> Of course you could go the other way and adjust dot gain in
StudioPrint to match your PS 
> gamma, but I was happy with the print contrast at 20% and so decided
to bring the 

> monitor in line.
> 
> amadou diallo

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Tyler Boley" <tyler@t...> 
wrote:
... 
> That's what kind of bugs me, we do it to taste instead of an accepted
> standard. We can both be linear, but be printing considerably lighter
> or darker than each other depending on our eyes. Of course we are
> editing our files to suit, but one would think there could be some
> widely accepted standard that once we are all linearized to, the same
> file would print similarly across the board.

I think we're using "linear" to mean reasonably smooth, so there's many
reasonably smooth curves from white to black.  For QTR I took a
strict sense of the word meaning a straight line when using Lab values.

Here's a reference that talks about it -- see #5  Lightness.
http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html

"The perceptual response to luminance is called lightness, and is 
defined by the CIE Publication ...  "
The text doesn't call it "Lab" but the formula given is exactly what shows
up in color formulas.

This isn't to say that's the only "correct" answer.  But it would be nice
if all our files would be printable under different systems.  From
what I've seen some systems end up printing a little lighter than
this -- i.e. the midtones are lighter than linear Lab.  I wouldn't be
surprised if this wasn't influenced by the thought "I want more
shadow detail" or "I want the print more luminous i.e. lighter".

Tyler, since you've picked the dot gain 20% for your linearized system.
I'm wondering how that compares with linear Lab.  For instance, on
one step wedge I have:  0 step = 97 L, 50 step = 57 L, 100 step =17 L.
So the 50 step is right in the middle.   What would your system give?

The trouble with all this is that no matter what you have that's what
your files are edited to so.   It's painful to switch even if you think its
the right thing to do.   I don't know how you can handle other
peoples files.

Roy

> Really outstanding single channel icc profiles would put much of this
> to rest, if we both had them, we could print the same file
> theoretically identically.
> 
....

> 
> > On thin ice now and in my own words.... Lab is "more or less"
> > perceptually linear.
> 
> I'm showing my lack of formal color education here, but I think you
> are right. I think LAB was developed over time to come as close as
> possible to human visual perception.
> 
> >  On top of that the approach by colour
> > management applications isn't always in respect of the shape's
> > construction. Gamut mapping for instance asks for a more
> > complicated approach with (3d?) curved mapping (or tables) to get
> > good perceptual hue matches. Most of the time it isn't done like
> > that and shifts like the blue > purple hue occur. Similar problem
> > with density dot gain.  Some polishing of the original
> > mathematical setup of Lab is also needed apparently. All Bruce
> > Lindbloom's territory...
> 
> Lindbloom to the rescue again. I ran some tests, if we assume LAB is
> perceptually uniform from gray values of 0,0,0 to 100,0,0, then middle
> gray must be somewhere near 50,0,0. This means a dot gain of something
> like 31+%, much more than I would have guessed. Some other tests in
> photoshop confirm this. So I'm not sure if that helps at all.
> I've come at this problem from every conceivable direction, including
> density.
> At this point I can only conclude that "linear" simply means that as
> tones progress they do so in a mathematically consistent manner. Other
> factors thrown in to make it perceptually desirable, like gamma or dot
> gain, remain subjective decisions.
> But that makes comparisons of systems based on those factors (it
> prints too light, or too dark) useless, particularly if it can be
> varied easily by the user but remain "linear".
> Tyler

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Peter" 
<spamme2001@m...> wrote:
> Thank you to everyone who replied to my message -- this is exactly 
> the discussion I was hoping for. 
> 
> For a variety of reasons I've decided that I'm not prepared for all 
> the control a RIP will provide, but I'd still like the ability to 
> tweak an existing profile to account for variances in paper batches 
> or the unique characteristics of my printer, for example. About a 
> year and a half ago I used the Curves Template located in the Files 
> section 
> (http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/files/Ima
> ge%20Processing/) to create a Photoshop adjustment layer but I 
> believe this spreadsheet does a strictly mathematical linearization.
> 
> I'm hoping to do something similar (i.e. measure the density values 
> in a stepwedge, compare to some Aims and make an adjustment curve) 
> but would like to account for perceptual issues. I'll see what I can 
> figure out with the Bruce Lindbloom calculators.

I don't know if this is really what you want, but I have a table of
my "ideal" densities for the 21 steps given a dMax.   It's in my
QTR download under CurveDesign, the file is called ideal_density.pdf

If you'd like, email me and I'll email the pdf to you.

Roy

> 
> Thanks again for your insight (and if you have any hints, I'm all 
> ears!).
> 
> Peter.
> 
> 
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Peter" 
> <spamme2001@m...> wrote:
> 
> > Is linearization supposed to be determined strictly 
> > mathematically or is there some element of perceptual 
> > linearization involved?

Roy

Can you tell me where to find the mathematics underlying the development of the table of 
ideal densities?

Thanks - Doug Nielsen

> I don't know if this is really what you want, but I have a table of
> my "ideal" densities for the 21 steps given a dMax.   It's in my
> QTR download under CurveDesign, the file is called ideal_density.pdf

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Doug Nielsen" 
<dougnielsen@c...> wrote:
> Roy
> 
> Can you tell me where to find the mathematics underlying the development of the 
table of 
> ideal densities?
> 
> Thanks - Doug Nielsen
> 
> 
> > I don't know if this is really what you want, but I have a table of
> > my "ideal" densities for the 21 steps given a dMax.   It's in my
> > QTR download under CurveDesign, the file is called ideal_density.pdf


The two main references that I've used are:
http://www.brucelindbloom.com/
http://www.easyrgb.com/math.html

There's a ton of stuff on these sites so it takes some exploring.
But the relevant formulas are:

Where L is Lab,  Y is luminance, d is density:
Y = ((L+16)/116)^3
d = -log10(Y)

So if you make the L's linear you get the d's in my table.

Roy

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington"
<roy@h...> wrote:
snip...
Roy, I think your approach using LAB is as sound as any other if not
more. I suspect many of the workflows used are based on a subjective
decision about what looks good, at least you are conforming to
something, and it also tends to look good.

> Tyler, since you've picked the dot gain 20% for your linearized system.
> I'm wondering how that compares with linear Lab.  For instance, on
> one step wedge I have:  0 step = 97 L, 50 step = 57 L, 100 step =17 L.
> So the 50 step is right in the middle.   What would your system give?

Give me a few days, I'm just changing inks around and relinearizing.
Since new ink is in, old linearizations won't be as relevant for this.

> The trouble with all this is that no matter what you have that's what
> your files are edited to so.   It's painful to switch even if you
think its
> the right thing to do.   I don't know how you can handle other
> peoples files.

I still think a color managed approach would help a great deal here.
It does work for color for the most part and I've used it for B&W. If
a file comes in tagged I can usually deal with it well, I've even
recieved RGB and CMYK files.
Tyler

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy 
Harrington" <roy@h...> wrote:

> I don't know if this is really what you want, but I have a table of
> my "ideal" densities for the 21 steps given a dMax.   It's in my
> QTR download under CurveDesign, the file is called 
ideal_density.pdf
> 
> If you'd like, email me and I'll email the pdf to you.
> 


Roy, is there any chance of getting  ideal–density.pdf posted in 
the files section of the group's page? 

I'm wrestling with the same problem, but I don't have OS X to 
support QTR. 

Allan Connery

This is exactly the chart I was going to make for myself. Thanks for 
saving me the trouble, Roy.

For comparison, I plotted Roy's ideal density measures along with my 
actual measures from output using the PiezoBW ICC profiles and Warm 
Neutral w/Museum Black ink. I printed a 21-step wedge on Epson 
Enhanced Matte, Epson Velvet Fine Art, Hahnemuhle Photo Rag, and 
Museum Bright White-148 paper (all measures taken after 24-48 hours 
of dry down). Several of the papers had different dMin values but I 
was mostly interested in seeing the approximate relationship between 
the curves.

Interestingly, the PiezoBW ICC profiles appear to have a very gentle 
S curve in relation to the Lab curve. For the most part, the values 
of K between 0 and 55% print below the Lab curve, cross over around 
60% and remain above the Lab curve through to 100%. Also of note, on 
each paper the 95% and 100% values measure approximately the same, 
which can be seen in slightly blocked-up shadows in my prints.

Here's a comparison of Roy's ideal densities (adjusted for a paper 
base of .05) and Hahnemuhle Photo Rag (HPR):

        Lab     HPR
0	0.05	0.05
5	0.10	0.10
10	0.15	0.14
15	0.20	0.19
20	0.25	0.23
25	0.30	0.29
30	0.36	0.34
35	0.42	0.39
40	0.48	0.45
45	0.55	0.50
50	0.62	0.52
55	0.69	0.58
60	0.77	0.70
65	0.85	0.86
70	0.94	1.02
75	1.04	1.21
80	1.14	1.34
85	1.25	1.45
90	1.37	1.57
95	1.50	1.66
100	1.65	1.63

Since the results from each of the PiezoBW ICC profiles was 
approximately the same I have to believe they did it on purpose ;~) 
I wonder if this is to account for specific perceptual issues that 
the Lab model doesn't account for?

Any thoughts?

Thanks,
Peter.


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy 
Harrington" <roy@h...> wrote:
> 
> I don't know if this is really what you want, but I have a table of
> my "ideal" densities for the 21 steps given a dMax.   It's in my
> QTR download under CurveDesign, the file is called 
ideal_density.pdf

> 
> If you'd like, email me and I'll email the pdf to you.
> 
> Roy
>

The "Lab" column is essentially what I use for all the inksets I've worked
on.

Paul
www.PaulRoark.com 

For UT2 information, curves, and settings see:
http://home1.gte.net/res09aij/
_____________________________________

-----Original Message-----
From: Peter [mailto:spamme2001@...] 
Sent: Tuesday, April 27, 2004 4:16 PM
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: [Digital BW] Re: Linearization - mathematical or perceptual?

This is exactly the chart I was going to make for myself. Thanks for 
saving me the trouble, Roy.

For comparison, I plotted Roy's ideal density measures along with my 
actual measures from output using the PiezoBW ICC profiles and Warm 
Neutral w/Museum Black ink. I printed a 21-step wedge on Epson 
Enhanced Matte, Epson Velvet Fine Art, Hahnemuhle Photo Rag, and 
Museum Bright White-148 paper (all measures taken after 24-48 hours 
of dry down). Several of the papers had different dMin values but I 
was mostly interested in seeing the approximate relationship between 
the curves.

Interestingly, the PiezoBW ICC profiles appear to have a very gentle 
S curve in relation to the Lab curve. For the most part, the values 
of K between 0 and 55% print below the Lab curve, cross over around 
60% and remain above the Lab curve through to 100%. Also of note, on 
each paper the 95% and 100% values measure approximately the same, 
which can be seen in slightly blocked-up shadows in my prints.

Here's a comparison of Roy's ideal densities (adjusted for a paper 
base of .05) and Hahnemuhle Photo Rag (HPR):

        Lab     HPR
0	0.05	0.05
5	0.10	0.10
10	0.15	0.14
15	0.20	0.19
20	0.25	0.23
25	0.30	0.29
30	0.36	0.34
35	0.42	0.39
40	0.48	0.45
45	0.55	0.50
50	0.62	0.52
55	0.69	0.58
60	0.77	0.70
65	0.85	0.86
70	0.94	1.02
75	1.04	1.21
80	1.14	1.34
85	1.25	1.45
90	1.37	1.57
95	1.50	1.66
100	1.65	1.63

Since the results from each of the PiezoBW ICC profiles was 
approximately the same I have to believe they did it on purpose ;~) 
I wonder if this is to account for specific perceptual issues that 
the Lab model doesn't account for?

Any thoughts?

Thanks,
Peter.


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy 
Harrington" <roy@h...> wrote:
> 
> I don't know if this is really what you want, but I have a table of
> my "ideal" densities for the 21 steps given a dMax.   It's in my
> QTR download under CurveDesign, the file is called 
ideal_density.pdf
> 
> If you'd like, email me and I'll email the pdf to you.
> 
> Roy
> 





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--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington"
<roy@h...> wrote:

> Tyler, since you've picked the dot gain 20% for your linearized
system.
> I'm wondering how that compares with linear Lab.  For instance, on
> one step wedge I have:  0 step = 97 L, 50 step = 57 L, 100 step =17
L.
> So the 50 step is right in the middle.   What would your system
give?

                                L          A           B
PaperWhite    98.3     0.1       1.4
50%gray          61.1     1.1       6.5
InkBlack           14.3     0.4    -1.6

I've included the a and b because this was from a linearization of my
warmest ink on a warm paper, and as you know accurate density is best
determined from spectral data. Since I don't have the spectral data
and real density for you the a and b is just to indicate the situation
though it may not be relevant. I am reconfiguring my printer and
haven't finished. Relinearizing the more neutral options on a whiter
paper, which might be a better comparison, is far from done. These
inks really settle in, dry down and get richer over a period of days
so all this takes time.
Anyway, dinking around in Photoshop and resetting these end points
seems to put my middle gray at around L 56, so I am printing lighter
than you.
These dot gain selections in StudioPrint are badly named, gamma would
probably have been a better choice. Dot gain is a very specifically
defined phenomena that occurs with ink on paper, and as we know a lot
of hoops have been hopped through to get a handle on it
mathematically. You can do things to try to offset it before printing
in a file, but it only occurs on paper during printing. It's not
really something you add with density adjustments. Just splitting
hairs here, but it adds to the confusion a it.
Don't know if the above contributes to the thread, but there we are.
Tyler

Sorry, the formatting made that very hard to read-
L A B
PaperWhite-   L=98.3,   A=0.1,   B=1.4
50%gray-   L=61.1,   A=1.1,   B=6.5
InkBlack-   L=14.3,   A=0.4,   B=-1.6
Tyler

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Tyler Boley" <tyler@t...> 
wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington"
> <roy@h...> wrote:
> 
> > Tyler, since you've picked the dot gain 20% for your linearized
> system.
> > I'm wondering how that compares with linear Lab.  For instance, on
> > one step wedge I have:  0 step = 97 L, 50 step = 57 L, 100 step =17
> L.
> > So the 50 step is right in the middle.   What would your system
> give?
> 
>                                 L          A           B
> PaperWhite    98.3     0.1       1.4
> 50%gray          61.1     1.1       6.5
> InkBlack           14.3     0.4    -1.6
> 
> I've included the a and b because this was from a linearization of my
> warmest ink on a warm paper, and as you know accurate density is best
> determined from spectral data. Since I don't have the spectral data
> and real density for you the a and b is just to indicate the situation
> though it may not be relevant. I am reconfiguring my printer and
> haven't finished. Relinearizing the more neutral options on a whiter
> paper, which might be a better comparison, is far from done. These
> inks really settle in, dry down and get richer over a period of days
> so all this takes time.
> Anyway, dinking around in Photoshop and resetting these end points
> seems to put my middle gray at around L 56, so I am printing lighter
> than you.
> These dot gain selections in StudioPrint are badly named, gamma would
> probably have been a better choice. Dot gain is a very specifically
> defined phenomena that occurs with ink on paper, and as we know a lot
> of hoops have been hopped through to get a handle on it
> mathematically. You can do things to try to offset it before printing
> in a file, but it only occurs on paper during printing. It's not
> really something you add with density adjustments. Just splitting
> hairs here, but it adds to the confusion a it.
> Don't know if the above contributes to the thread, but there we are.
> Tyler

Thanks, Tyler.  It does confirm that you and Steve are linearizing such
that the same file would print lighter.  In practice, of course, we edit the
files to print as we like.

It looks like StudioPrint allows you to linearize to various dot gains
giving different overall lightnesses.  I wonder what the color profiler
programs do with this.  It ought to be done the same if there's an
accepted standard.

Roy

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington"
<roy@h...> wrote:
snip...
> It looks like StudioPrint allows you to linearize to various dot gains
> giving different overall lightnesses.  I wonder what the color profiler
> programs do with this.  It ought to be done the same if there's an
> accepted standard.

Shouldn't matter, we're simply saying we're sending these particular
numbers to the device, in both the chart and the reference, and the
profiler shows us what the device does with them. 
So if I linearize to a different dot gain out, and reprofile for that,
the "preserve color numbers" should reflect that difference. Same as
if you had profiled to a different device or output method, yours vrs
mine, or SP 10% vrs SP 20%, etc..
Maybe the point is that if the DG is changed, reprofiling is necessary
as it's really now a different device.
Hope that makes sense.
Tyler

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Tyler Boley" <tyler@t...> wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington"
> <roy@h...> wrote:
> snip...
> > It looks like StudioPrint allows you to linearize to various dot gains
> > giving different overall lightnesses.  I wonder what the color profiler
> > programs do with this.  It ought to be done the same if there's an
> > accepted standard.
> 
> Shouldn't matter, we're simply saying we're sending these particular
> numbers to the device, in both the chart and the reference, and the
> profiler shows us what the device does with them. 
> So if I linearize to a different dot gain out, and reprofile for that,
> the "preserve color numbers" should reflect that difference. Same as
> if you had profiled to a different device or output method, yours vrs
> mine, or SP 10% vrs SP 20%, etc..
> Maybe the point is that if the DG is changed, reprofiling is necessary
> as it's really now a different device.
> Hope that makes sense.
> Tyler

Sure.  You can make any of the situations work for you.
I was just thinking that if someone already had a file they had
worked on in a color managed environment, it would be nice if they
got very close when they tried to move over to one of our B&W
managed environments.

Roy

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Roy Harrington"
<roy@h...> wrote:
...
> Sure.  You can make any of the situations work for you.
> I was just thinking that if someone already had a file they had
> worked on in a color managed environment, it would be nice if they
> got very close when they tried to move over to one of our B&W
> managed environments.

Right, sorry. I suspect you will be closer than I since you linearize
to LAB, since that's the reference for all icc profile conversions. As
long as any file is tagged though, I can convert it to print to match.
That's the idea anyway. In the reall world I've seen icc profiles that
don't print identically in terms of lightness, though they should. And
even though I convert all kinds of files here to my 20% gray space I
still usually have to do a slight bit of work after.
If you can make a custom dot gain grayscale space in PS that
corresponds precisely to LAB and save it out as a profile, you should
be able to do the same there. For that matter, if a file of yours came
in here tagged with that space, theoretically I could convert to 20%
and match.
I just hardware calibrated and profiled my monitor twice within a half
hour, and the two profiles don't look the same, so all of this still
has a ways to go. When I make color profiles I measure the chart
several times and then average them in Measure tool, sometimes it's
suprising how different they are.
My i1 just got back from a repair in Switzerland and is already acting
up a bit. I've had it about 9 months, it's been replaced once and
repaired once, and is not acting healthy today. My confidence in all
this is low today, so is my bank account.
Tyler