QTR-Quadtone RIP

Again, I found I am answering some of my own
questions posted to this list.

1. Convert or Not Convert?

In Mac OS X QTR Printing Tutorial ("Tutorial.pdf"),
the instruction is clear that we should let Photoshop
manage the color and convert the source image profile
to either "QTR Gray Matte Paper" or "QTR Gray Photo
Paper", Roy's standard QTR device profiles.  There is
also a separate instruction sheet explaining the
switching from using no such conversion ("No Color
Management" or "Same As Source" in Photoshop) to
using the standard profiles, a change made not long
ago, to address the different visual characteristics
of matte and photo paper, and for other purposes.

The QTR profiles come with a Gamma close to 2.5, so
unless you work in the same color space in your
source images the numbers will change during the
conversion process, stretching the lower midtone and
shadows little bit and compress the highlight
slightly when the source image profile has a Gamma
of 2.2, much more so when it is 1.8.  You can easily
watch such changes in your histograms.

If such conversion is an intrinsic necessary step in
the QTR printing workflow now, we would be logically
thinking that all the linearizations needs to be done
also with the same conversion in place.

But, on top of Page two, Roy instructed us not to do
so when linearize: "Print targets with QTR and all
the selections you want to profile or linearize. The
intended resolution is very important. The targets
are Untagged and should NOT be color managed in any
way. Do not Convert an image. Always print with No
Color Management or Same As Source."

After letting targets to dry for 48 hours, my
Eye-One measurements last night confirmed that,
the Roy's default QTR curves, at least for Epson
3800 for the papers I am dealing, were linearized
with no conversions.  When we print either the 21-
or the 51-step target with the default curves and
no conversions to the Gray Matte/Photo Paper
profile, the resulting linearity were nearly ideal
(ruler straight lines), while when the conversion is
inserted to the workflow, the resulting linearization
is off with reduced shadow separations (the lines
bend down at lower left, the high density region).

So, the conclusion is, we should NOT perform the
conversion described in the Tutorial, when the
source image Gamma is 2.2 and the default QTR curves
are used.  If you work on Gamma 1.8 you should first
convert the images to Gamma 2.2.  Thus, I believe the
Tutorial needs to be updated.

Then the question remains: what happens if we keep
the conversion in the printing process, but to build
costume QTR curves to fit the workflow?  I did more
experiments along this line, and found it not a good
idea.

First, for the Hahnemuhle Photo Rag 308 paper I am
mainly interested in with the Epson UC K3 matte ink,
and with the QTR Gray Matte Photo profile, it is
impossible to linearize in the K=95-100 region.
Looking through the Mac OS X's ColorSync utility,
the QTR Gray LAB and the QTR Gray Photo Paper
profiles contain gray transfer curves that start
from the origin (X=Y=0) while the QTR Gray Matte
Paper profile has a small intercept (X=0, Y=2 or 3).

With the conversion to the QTR Gray Matte profile,
this small gap in the transfer curve compresses all
the K values below 2 or 3, or RGB values below
around 5 or 6, to 0.  This is again easily seen with
the Photoshop histograms.  Such crushing of deep
shadow values may help some matte QTR print's looking,
but analytically makes linearization in the dark
shadow region impossible.  The pre-linearization
readings at K=95 and K=100 are always identical with
the curve (naturally), and as a matter of fact the
pre-linearization curves are almost vertical in the
K=85-100 region, making the inversion of the curves
difficult or impossible.

The real world results with the small intercept in
the profile is (A) the resulting linearization is
not mathematically stable, (B) the QTR curve making
program often fail in making the curves (.quad files)
from the curve description text source with the
measured linearization values in place, for a stated
reason in the error message that the linearization
values do not decrease monotonously (in the dark
shadow region), and (C) even when the linearized
curves are successfully made, the test results with
these curves are not good - still no tonal separation
between K=95 and K=100, since the QTR Gray Matte
Paper curve always brings them (nearly)together!

Actually when the (B) happens, the linearization
data is monotonically decreasing, but obviously the
differentials in the deep dark region are too small
so some kind of fitting routine failed inside the
program.  Also, when the conversion is in the
workflow, the resulting linearized curves produce
higher density at K=50 (around 0.61 against the
0.58 with the linearized curves without the
conversion, which is closer to the ideal value of
0.568), indicating Gamma value errors.

This re-confirmed that, the QTR curves should be
always used WITHOUT converting the source image to
the QTR's GRAY paper profiles, just keeping the
source image Gamma at 2.2 and print in Photoshop
with "No Color Management" to QTR driver, when
printing images, AND when making new curves, AND
when performing linearization.

2. Ink Limits, Black Boost, and D-Max

I also explored heavily on the effects of the QTR
curve's K Ink Limit and Black Boost settings.

The general result is that, we can gain a bit
D-Max from raising the K Ink Limit of the default
curves by 10 (45 to 55, 50 to 60, and 55 to 65)
and maximizing the Black Boost values to 100.

As Roy pointed out, the D-Max actually decreases,
when the ink limits are set too high, such as
typically 75 and higher for K.  Also, the overlap
of the inks does not raise the D-Max but only mess
up other things.

Here are the typical D-Max values I am getting from
the Eye-One measurements (the "Warm" curves tend to
produce the highest D-Max, since it uses no color
inks).  "Boost" means both increasing the K Ink Limit
by 10 from the original values, and setting the
Black Boost to 100.

       Paper         Ink   Driver    Boost     D-Max
------------------  -----  ------  ----------  -----
Hah PhotoRag 308    Matte   ABW        -       1.59
                            QTR        NO      1.55
                            QTR        YES     1.61

Museo Silver Rag    Gloss   ABW        -       2.21
                            QTR        NO      1.94
                            QTR        YES     2.47

Hah FineArt Pearl   Gloss   ABW        -       2.04
                            QTR        NO      1.92
                            QTR        YES     2.15

Ilford Smooth Pearl Gloss   ABW        -       2.23
                            QTR        NO      2.05
                            QTR        YES     2.44

Epson PLPP          Gloss   ABW        -       2.25
                            QTR        NO      2.08
                            QTR        YES     2.47

Remember every 0.3 increase of the D-Max is one
stop darker (double the density).

Thanks,
Leping

Hi Leping,

You've got a lot of inter-related issues going on and I think they tend 
to
confuse the situation.

In QTR there are two similar but different features.   First, there's 
the
Linearization in the QTR profiles and second, there's the ICC profiling
with either generic QTR Gray Matte/Photo Paper profiles or custom
Create-ICC profiles.

On Thursday, May 3, 2007, at 01:02  PM, Leping Zha wrote:

> Again, I found I am answering some of my own
> questions posted to this list.
>
> 1. Convert or Not Convert?
>
> In Mac OS X QTR Printing Tutorial ("Tutorial.pdf"),
> the instruction is clear that we should let Photoshop
> manage the color and convert the source image profile
> to either "QTR Gray Matte Paper" or "QTR Gray Photo
> Paper", Roy's standard QTR device profiles.  There is
> also a separate instruction sheet explaining the
> switching from using no such conversion ("No Color
> Management" or "Same As Source" in Photoshop) to
> using the standard profiles, a change made not long
> ago, to address the different visual characteristics
> of matte and photo paper, and for other purposes.
>
> The QTR profiles come with a Gamma close to 2.5, so

QTR profiles don't use a gamma function which is a pure exponential.
QTR linearization uses the Lab L* function.   The idea being to
make a straight-line in L measurements.  The line always goes
from dMin to dMax and the goal is a simple straight-line.
Gamma functions are a different shape.

> unless you work in the same color space in your
> source images the numbers will change during the
> conversion process, stretching the lower midtone and
> shadows little bit and compress the highlight
> slightly when the source image profile has a Gamma
> of 2.2, much more so when it is 1.8.  You can easily
> watch such changes in your histograms.
>
> If such conversion is an intrinsic necessary step in
> the QTR printing workflow now, we would be logically
> thinking that all the linearizations needs to be done
> also with the same conversion in place.
>
> But, on top of Page two, Roy instructed us not to do
> so when linearize: "Print targets with QTR and all
> the selections you want to profile or linearize. The
> intended resolution is very important. The targets
> are Untagged and should NOT be color managed in any
> way. Do not Convert an image. Always print with No
> Color Management or Same As Source."

This is specifically for printing targets that will be used for
linearization or ICC profiles.  You need to get "raw" density
measurements so that a curve can be fitted to correct/linearize
the output.

>
> After letting targets to dry for 48 hours, my
> Eye-One measurements last night confirmed that,
> the Roy's default QTR curves, at least for Epson
> 3800 for the papers I am dealing, were linearized
> with no conversions.  When we print either the 21-
> or the 51-step target with the default curves and
> no conversions to the Gray Matte/Photo Paper
> profile, the resulting linearity were nearly ideal
> (ruler straight lines), while when the conversion is
> inserted to the workflow, the resulting linearization
> is off with reduced shadow separations (the lines
> bend down at lower left, the high density region).
>
> So, the conclusion is, we should NOT perform the
> conversion described in the Tutorial, when the
> source image Gamma is 2.2 and the default QTR curves
> are used.  If you work on Gamma 1.8 you should first
> convert the images to Gamma 2.2.  Thus, I believe the
> Tutorial needs to be updated.

It sounds like what you are doing is measuring a stepwedge for
Lab linearity.  Since Lab linearity is what the basic QTR profile
goal is then naturally you'll get the best linearity with just the
basic QTR profile and No Color Management conversions.

Color Management and ICC profiles however have a different
purpose and goal.  It's much harder to measure the precise result
because the goal is matching of our perception not a specific
linearity.

When you print on matte paper there's a mapping of dMin's and dMax's
from the file to the paper.  In general you lose more at the shadow/dMax
end.  So with straight QTR profiles this will usually mean a lighter 
print
because the straight-line pushes the whole range lighter.  The idea
of Color Management is to do a mapping that better (but not perfectly)
matches our perception.  This sacrifices some of the shadow separation
in favor of midrange density.

In addition to this issue you also have to consider the source embedded
profile (or working space for untagged files).  Say you have a stepwedge
and look at K=95, it's really the corresponding L value that determines
how dark it is.  So for Gamma 2.2 there is very little separation 
between
K=100 and K=95.  Look at the eye-dropper in Photoshop, the difference
is only L=0 to L=1 -- much less than the separation between any other
steps.

The bottom line with all color management issues is how good the print
and the screen match with our perception not measurements with a
densitometer.

Roy

>
> Then the question remains: what happens if we keep
> the conversion in the printing process, but to build
> costume QTR curves to fit the workflow?  I did more
> experiments along this line, and found it not a good
> idea.
>
> First, for the Hahnemuhle Photo Rag 308 paper I am
> mainly interested in with the Epson UC K3 matte ink,
> and with the QTR Gray Matte Photo profile, it is
> impossible to linearize in the K=95-100 region.
> Looking through the Mac OS X's ColorSync utility,
> the QTR Gray LAB and the QTR Gray Photo Paper
> profiles contain gray transfer curves that start
> from the origin (X=Y=0) while the QTR Gray Matte
> Paper profile has a small intercept (X=0, Y=2 or 3).
>
> With the conversion to the QTR Gray Matte profile,
> this small gap in the transfer curve compresses all
> the K values below 2 or 3, or RGB values below
> around 5 or 6, to 0.  This is again easily seen with
> the Photoshop histograms.  Such crushing of deep
> shadow values may help some matte QTR print's looking,
> but analytically makes linearization in the dark
> shadow region impossible.  The pre-linearization
> readings at K=95 and K=100 are always identical with
> the curve (naturally), and as a matter of fact the
> pre-linearization curves are almost vertical in the
> K=85-100 region, making the inversion of the curves
> difficult or impossible.
>
> The real world results with the small intercept in
> the profile is (A) the resulting linearization is
> not mathematically stable, (B) the QTR curve making
> program often fail in making the curves (.quad files)
> from the curve description text source with the
> measured linearization values in place, for a stated
> reason in the error message that the linearization
> values do not decrease monotonously (in the dark
> shadow region), and (C) even when the linearized
> curves are successfully made, the test results with
> these curves are not good - still no tonal separation
> between K=95 and K=100, since the QTR Gray Matte
> Paper curve always brings them (nearly)together!
>
> Actually when the (B) happens, the linearization
> data is monotonically decreasing, but obviously the
> differentials in the deep dark region are too small
> so some kind of fitting routine failed inside the
> program.  Also, when the conversion is in the
> workflow, the resulting linearized curves produce
> higher density at K=50 (around 0.61 against the
> 0.58 with the linearized curves without the
> conversion, which is closer to the ideal value of
> 0.568), indicating Gamma value errors.
>
> This re-confirmed that, the QTR curves should be
> always used WITHOUT converting the source image to
> the QTR's GRAY paper profiles, just keeping the
> source image Gamma at 2.2 and print in Photoshop
> with "No Color Management" to QTR driver, when
> printing images, AND when making new curves, AND
> when performing linearization.
>
> 2. Ink Limits, Black Boost, and D-Max
>
> I also explored heavily on the effects of the QTR
> curve's K Ink Limit and Black Boost settings.
>
> The general result is that, we can gain a bit
> D-Max from raising the K Ink Limit of the default
> curves by 10 (45 to 55, 50 to 60, and 55 to 65)
> and maximizing the Black Boost values to 100.
>
> As Roy pointed out, the D-Max actually decreases,
> when the ink limits are set too high, such as
> typically 75 and higher for K.  Also, the overlap
> of the inks does not raise the D-Max but only mess
> up other things.
>
> Here are the typical D-Max values I am getting from
> the Eye-One measurements (the "Warm" curves tend to
> produce the highest D-Max, since it uses no color
> inks).  "Boost" means both increasing the K Ink Limit
> by 10 from the original values, and setting the
> Black Boost to 100.
>
>        Paper         Ink   Driver    Boost     D-Max
> ------------------  -----  ------  ----------  -----
> Hah PhotoRag 308    Matte   ABW        -       1.59
>                             QTR        NO      1.55
>                             QTR        YES     1.61
>
> Museo Silver Rag    Gloss   ABW        -       2.21
>                             QTR        NO      1.94
>                             QTR        YES     2.47
>
> Hah FineArt Pearl   Gloss   ABW        -       2.04
>                             QTR        NO      1.92
>                             QTR        YES     2.15
>
> Ilford Smooth Pearl Gloss   ABW        -       2.23
>                             QTR        NO      2.05
>                             QTR        YES     2.44
>
> Epson PLPP          Gloss   ABW        -       2.25
>                             QTR        NO      2.08
>                             QTR        YES     2.47
>
> Remember every 0.3 increase of the D-Max is one
> stop darker (double the density).
>
> Thanks,
> Leping
>
-
Roy Harrington
roy@...
Black & White Photo Gallery
http://www.harrington.com

Hi Roy,

Thank you so much for responding, and confirming that:

1. The linearization targets should be printed "raw" without
   any color management.

2. The linearization results (after inserting the linearize
   line to the source text file of the curves, remaking and
   installing the curves, and restart Photoshop) shoule be
   also measured "raw" without color management, for the
   objective of Lab linearity.

Since my densitometer is borrowed, I have been concentrating
in understanding the linearization process.  As you pointed
out, what really matters is how the real prints look, or match
the display on screen on different types of paper, the area
I have not explored yet.  It is then more in the area of
artistic preference, or personal taste, wheather to use the
QTR Matte/Photo Paper curves for printing, which is no more
in the domain of analytical discussion.  Some of my friends
have told me they have been happy printing with QTR curves
without the profile conversion, but some may perfer to do so,
I guess.

The only question remaining right now to me is that, with the
only tool I have to exam the ICC profiles, the OS X ColorSync,
your QTR Gray curves simply contain a gray transfer curve that
do not look linear.  They are probably not pure explential,
but I measured the interceptions and found it is close to
a Gamma 2.5 curve from calculations.  I put the curve side
by side to the Gamma 2.2 and 1.8 curves trying to understand
the differences, and certainly they look much closer to the
2.2 curve, with the exception of the small interception at
near the origin in the Matte Paper profile.  Then I measured
the difference of the QTR curve relative to Gamma 2.2, and
predicted it would crush in some extremely low shadows to
pure black (from the interception), but expand the other
shadow values, and compress the mid-highlight a little bit so
the prints would be a bit brighter in midtones.  Next, I
watched the spiked histogram line shifts with a gray step
wedge image before and after converting (from the untagged
file under my working space that is Gamma 2.2, to the QTR
Matte Paper profile), that confirmed these predictions.

If a profile is identical to Gray Gamma 2.2, for instance,
the conversion from the Gray Gamma 2.2 to it does nothing.
If your profile is a "linear" curve, a conversion to it from
the Gamma 2.2 work space changes the numbers a lot before they
are fed to the QTR engine.  Since converting to the QTR
profile in your specified QTR printing workflow only changes
the print's looking little bit, as you described, can we say
that the profiles are closer to the Gamma 2.2 ones than being
"linear", even they are linear to the Lab values?

Many thanks again,
Leping

--- In QuadtoneRIP@yahoogroups.com, Roy Harrington <roy@...> wrote:

>
> Hi Leping,
> 
> You've got a lot of inter-related issues going on and I think
> they tend to confuse the situation.
> 
> In QTR there are two similar but different features.   First,
> there's the Linearization in the QTR profiles and second,
> there's the ICC profiling with either generic QTR Gray
> Matte/Photo Paper profiles or custom Create-ICC profiles.
 
> QTR profiles don't use a gamma function which is a pure
> exponential.  QTR linearization uses the Lab L* function.
> The idea being to make a straight-line in L measurements.
> The line always goes from dMin to dMax and the goal is a
> simple straight-line.  xGamma functions are a different shape.

> This is specifically for printing targets that will be used for
> linearization or ICC profiles.  You need to get "raw" density
> measurements so that a curve can be fitted to correct/linearize
> the output.

> It sounds like what you are doing is measuring a stepwedge for
> Lab linearity.  Since Lab linearity is what the basic QTR profile
> goal is then naturally you'll get the best linearity with just the
> basic QTR profile and No Color Management conversions.
> 
> Color Management and ICC profiles however have a different
> purpose and goal.  It's much harder to measure the precise result
> because the goal is matching of our perception not a specific
> linearity.
> 
> When you print on matte paper there's a mapping of dMin's and
> dMax's from the file to the paper.  In general you lose more at
> the shadow/dMax end.  So with straight QTR profiles this will
> usually mean a lighter print because the straight-line pushes
> the whole range lighter.  The idea of Color Management is to
> do a mapping that better (but not perfectly) matches our
> perception.  This sacrifices some of the shadow separation
> in favor of midrange density.
> 
> In addition to this issue you also have to consider the source
> embedded profile (or working space for untagged files).  Say
> you have a stepwedge and look at K=95, it's really the
> corresponding L value that determines how dark it is.  So for
> Gamma 2.2 there is very little separation between K=100 and
> K=95.  Look at the eye-dropper in Photoshop, the difference
> is only L=0 to L=1 -- much less than the separation between
> any other steps.
> 
> The bottom line with all color management issues is how good
> the print and the screen match with our perception not
> measurements with a densitometer.
> 
> Roy

Hi Leping,

If you want to get into understanding the internals of ICC profiles 
there are a couple of
terms and definitions that are worth getting used to.

Y = Luminance,  the gray part of XYZ,  usually 0...1
    this is a basic physical property, the fraction of photons reflected 
from a surface
L = Luminosity or L*, part of LAB,  usually 0...100
    this is linear with human perception.

some standard formulas:
density = -log10(Y)
Y =  ((L+16)/116)^3   for L >= 8
Y =  L/903.3  for L<8

A good website for more of the math and some explanations is:
    http://www.brucelindbloom.com/

The ICC profiles can be based on either XYZ or Lab.  You can see this 
in the header.
-- the generic qtr icc's are XYZ,  but the custom ones from 
QTR-Create-ICC are Lab.

When you have a gamma based profile, its simply:
    datavalue = Y^gamma    or  Y=datavalue^(1/gamma)
where datavalues are logically 0...1  (in 8 bit that would be stored 
0...255)

------------------------------------

When people talk about "linear" they imply linear in Y or L but don't 
typically say which.
QTR curve linearization is linear in L values.  In the ICC files CM is 
does
interpolation with linear L values, but expansion/contraction of dMin & 
dMax is
done with linear Y values.  Why all the complication?  Mostly because 
that's
what works the best.

If you are comfortable with lots of math conversions this is not as bad 
as it may sound
but most people would rather just see it all as a magic black box.

Roy

On Friday, May 4, 2007, at 12:26  PM, Leping Zha wrote:

> Hi Roy,
>
> Thank you so much for responding, and confirming that:
>
> 1. The linearization targets should be printed "raw" without
>    any color management.
>
> 2. The linearization results (after inserting the linearize
>    line to the source text file of the curves, remaking and
>    installing the curves, and restart Photoshop) shoule be
>    also measured "raw" without color management, for the
>    objective of Lab linearity.
>
> Since my densitometer is borrowed, I have been concentrating
> in understanding the linearization process.  As you pointed
> out, what really matters is how the real prints look, or match
> the display on screen on different types of paper, the area
> I have not explored yet.  It is then more in the area of
> artistic preference, or personal taste, wheather to use the
> QTR Matte/Photo Paper curves for printing, which is no more
> in the domain of analytical discussion.  Some of my friends
> have told me they have been happy printing with QTR curves
> without the profile conversion, but some may perfer to do so,
> I guess.
>
> The only question remaining right now to me is that, with the
> only tool I have to exam the ICC profiles, the OS X ColorSync,
> your QTR Gray curves simply contain a gray transfer curve that
> do not look linear.  They are probably not pure explential,
> but I measured the interceptions and found it is close to
> a Gamma 2.5 curve from calculations.  I put the curve side
> by side to the Gamma 2.2 and 1.8 curves trying to understand
> the differences, and certainly they look much closer to the
> 2.2 curve, with the exception of the small interception at
> near the origin in the Matte Paper profile.  Then I measured
> the difference of the QTR curve relative to Gamma 2.2, and
> predicted it would crush in some extremely low shadows to
> pure black (from the interception), but expand the other
> shadow values, and compress the mid-highlight a little bit so
> the prints would be a bit brighter in midtones.  Next, I
> watched the spiked histogram line shifts with a gray step
> wedge image before and after converting (from the untagged
> file under my working space that is Gamma 2.2, to the QTR
> Matte Paper profile), that confirmed these predictions.
>
> If a profile is identical to Gray Gamma 2.2, for instance,
> the conversion from the Gray Gamma 2.2 to it does nothing.
> If your profile is a "linear" curve, a conversion to it from
> the Gamma 2.2 work space changes the numbers a lot before they
> are fed to the QTR engine.  Since converting to the QTR
> profile in your specified QTR printing workflow only changes
> the print's looking little bit, as you described, can we say
> that the profiles are closer to the Gamma 2.2 ones than being
> "linear", even they are linear to the Lab values?
>
> Many thanks again,
> Leping
>
> --- In QuadtoneRIP@yahoogroups.com, Roy Harrington <roy@...> wrote:
>>
>> Hi Leping,
>>
>> You've got a lot of inter-related issues going on and I think
>> they tend to confuse the situation.
>>
>> In QTR there are two similar but different features.   First,
>> there's the Linearization in the QTR profiles and second,
>> there's the ICC profiling with either generic QTR Gray
>> Matte/Photo Paper profiles or custom Create-ICC profiles.
>
>> QTR profiles don't use a gamma function which is a pure
>> exponential.  QTR linearization uses the Lab L* function.
>> The idea being to make a straight-line in L measurements.
>> The line always goes from dMin to dMax and the goal is a
>> simple straight-line.  xGamma functions are a different shape.
>
>> This is specifically for printing targets that will be used for
>> linearization or ICC profiles.  You need to get "raw" density
>> measurements so that a curve can be fitted to correct/linearize
>> the output.
>
>> It sounds like what you are doing is measuring a stepwedge for
>> Lab linearity.  Since Lab linearity is what the basic QTR profile
>> goal is then naturally you'll get the best linearity with just the
>> basic QTR profile and No Color Management conversions.
>>
>> Color Management and ICC profiles however have a different
>> purpose and goal.  It's much harder to measure the precise result
>> because the goal is matching of our perception not a specific
>> linearity.
>>
>> When you print on matte paper there's a mapping of dMin's and
>> dMax's from the file to the paper.  In general you lose more at
>> the shadow/dMax end.  So with straight QTR profiles this will
>> usually mean a lighter print because the straight-line pushes
>> the whole range lighter.  The idea of Color Management is to
>> do a mapping that better (but not perfectly) matches our
>> perception.  This sacrifices some of the shadow separation
>> in favor of midrange density.
>>
>> In addition to this issue you also have to consider the source
>> embedded profile (or working space for untagged files).  Say
>> you have a stepwedge and look at K=95, it's really the
>> corresponding L value that determines how dark it is.  So for
>> Gamma 2.2 there is very little separation between K=100 and
>> K=95.  Look at the eye-dropper in Photoshop, the difference
>> is only L=0 to L=1 -- much less than the separation between
>> any other steps.
>>
>> The bottom line with all color management issues is how good
>> the print and the screen match with our perception not
>> measurements with a densitometer.
>>
>> Roy
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
-
Roy Harrington
roy@...
Black & White Photo Gallery
http://www.harrington.com