Digital BW, The Print

Hi,

I am attempting to calibrate my printer output using a calibrated X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize that this question has come up in the past, but practical elements of technique were omitted.  Below you will find the reflective densitometer (visual) output vs a 21 step stepwedge.  I did measurements using both the Randall and Piezography workflows.  If you look at the numbers carefully, you will conclude as to how shockingly non-linear they are.  I would have expected, for example that the 50 % reading would have been close to 1.7/2 = .85.  The Measured value of around 0.6 is WAY off!

Has anyone else had this experience? I would not think that my paper choice would have that much effect.  Are there subtle differences in using a reflective densitometer as opposed to a spectrophotometer to do the measurements? It would seem that for grayscale work that a densitometer should be fine.  Please advise.

Thanks!

-John Chervinsky



STEPWEDGE  CONE      RANDALL
100.0     	1.71     	1.77
95.00     	1.54     	1.66
90.00	     1.40     	1.57
85.00	     1.26     	1.45
80.00	     1.15     	1.33
75.00	     1.05	     1.20
70.00     	0.96     	1.07
65.00	     0.86     	0.95
60.00     	0.78	     0.83
55.00     	0.69      0.76
50.00	     0.61     	0.66
45.00	     0.54     	0.58
40.00	     0.48	     0.48
35.00	     0.42     	0.39
30.00     	0.36	     0.32
25.00     	0.29      0.27
20.00	     0.24     	0.21
15.00	     0.19	     0.17
10.00      0.14      0.13
5.00	      0.09	     0.09
0.00	      0.05	     0.05

Hi,

I am attempting to calibrate my printer output using a calibrated
X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 1160
onto PhotoRag 308 paper; I am on a Mac computer.  I realize that this
question has come up in the past, but practical elements of technique
were omitted.  Below you will find the reflective densitometer
(visual) output vs a 21 step stepwedge.  I did measurements using both
the Randall and Piezography workflows.  If you look at the numbers
carefully, you will conclude as to how shockingly non-linear they are.
 I would have expected, for example that the 50 % reading would have
been close to 1.7/2 = .85.  The Measured value of around 0.6 is WAY
off!

Has anyone else had this experience? I would not think that my paper
choice would have that much effect.  Are there subtle differences in
using a reflective densitometer as opposed to a spectrophotometer to
do the measurements? It would seem that for grayscale work that a
densitometer should be fine.  Please advise.

Thanks!

-John Chervinsky



STEPWEDGE  CONE      RANDALL
100.0     	1.71     	1.77
95.00     	1.54     	1.66
90.00           1.40     	1.57
85.00           1.26     	1.45
80.00           1.15     	1.33
75.00           1.05	        1.20
70.00     	0.96     	1.07
65.00           0.86     	0.95
60.00     	0.78	        0.83
55.00     	0.69            0.76
50.00           0.61     	0.66
45.00           0.54     	0.58
40.00           0.48	        0.48
35.00           0.42     	0.39
30.00     	0.36	        0.32
25.00     	0.29            0.27
20.00           0.24     	0.21
15.00           0.19	        0.17
10.00           0.14            0.13
5.00            0.09	        0.09
0.00            0.05	        0.05

John,
You are at the same point as I am. Well, actually I'm a little 
ahead. The density readings are log to the base 10 so dividing the 
Dmax by 2 will not give you the expected 50% reading. I am currently 
trying to figure out the math.
I will let you know when I get there,

Barry

--- In DigitalBlackandWhiteThePrint@y..., John Chervinsky 
<chervinsky@d...> wrote:
> Hi,
> 
> I am attempting to calibrate my printer output using a calibrated 
X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 
1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize 
that this question has come up in the past, but practical elements 
of technique were omitted.  Below you will find the reflective 
densitometer (visual) output vs a 21 step stepwedge.  I did 
measurements using both the Randall and Piezography workflows.  If 
you look at the numbers carefully, you will conclude as to how 
shockingly non-linear they are.  I would have expected, for example 
that the 50 % reading would have been close to 1.7/2 = .85.  The 
Measured value of around 0.6 is WAY off!
> 
> Has anyone else had this experience? I would not think that my 
paper choice would have that much effect.  Are there subtle 
differences in using a reflective densitometer as opposed to a 
spectrophotometer to do the measurements? It would seem that for 
grayscale work that a densitometer should be fine.  Please advise.

> 
> Thanks!
> 
> -John Chervinsky
> 
> 
> 
> STEPWEDGE  CONE      RANDALL
> 100.0     	1.71     	1.77
> 95.00     	1.54     	1.66
> 90.00	     1.40     	1.57
> 85.00	     1.26     	1.45
> 80.00	     1.15     	1.33
> 75.00	     1.05	     1.20
> 70.00     	0.96     	1.07
> 65.00	     0.86     	0.95
> 60.00     	0.78	     0.83
> 55.00     	0.69      0.76
> 50.00	     0.61     	0.66
> 45.00	     0.54     	0.58
> 40.00	     0.48	     0.48
> 35.00	     0.42     	0.39
> 30.00     	0.36	     0.32
> 25.00     	0.29      0.27
> 20.00	     0.24     	0.21
> 15.00	     0.19	     0.17
> 10.00      0.14      0.13
> 5.00	      0.09	     0.09
> 0.00	      0.05	     0.05

This might help. 
 optical density (OD): For a given wavelength, an expression of the 
transmittance of an optical element. Note 1: Optical density is 
expressed by log10(1/T ) where T is transmittance. (188) Note 2: The 
higher the optical density, the lower the transmittance. Note 3: 
Optical density times 10 is equal to transmission loss expressed in 
decibels, e.g. , an optical density of 0.3 corresponds to a 
transmission loss of 3 dB. Def of optical density.

Jeff




> John,
> You are at the same point as I am. Well, actually I'm a little 
> ahead. The density readings are log to the base 10 so dividing the 
> Dmax by 2 will not give you the expected 50% reading. I am 
currently 

> trying to figure out the math.
> I will let you know when I get there,
> 
> Barry
> 
> --- In DigitalBlackandWhiteThePrint@y..., John Chervinsky 
> <chervinsky@d...> wrote:
> > Hi,
> > 
> > I am attempting to calibrate my printer output using a calibrated 
> X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 
> 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize 
> that this question has come up in the past, but practical elements 
> of technique were omitted.  Below you will find the reflective 
> densitometer (visual) output vs a 21 step stepwedge.  I did 
> measurements using both the Randall and Piezography workflows.  If 
> you look at the numbers carefully, you will conclude as to how 
> shockingly non-linear they are.  I would have expected, for example 
> that the 50 % reading would have been close to 1.7/2 = .85.  The 
> Measured value of around 0.6 is WAY off!
> > 
> > Has anyone else had this experience? I would not think that my 
> paper choice would have that much effect.  Are there subtle 
> differences in using a reflective densitometer as opposed to a 
> spectrophotometer to do the measurements? It would seem that for 
> grayscale work that a densitometer should be fine.  Please advise.
> > 
> > Thanks!
> > 
> > -John Chervinsky
> > 
> > 
> > 
> > STEPWEDGE  CONE      RANDALL
> > 100.0     	1.71     	1.77
> > 95.00     	1.54     	1.66
> > 90.00	     1.40     	1.57
> > 85.00	     1.26     	1.45
> > 80.00	     1.15     	1.33
> > 75.00	     1.05	     1.20
> > 70.00     	0.96     	1.07
> > 65.00	     0.86     	0.95
> > 60.00     	0.78	     0.83
> > 55.00     	0.69      0.76
> > 50.00	     0.61     	0.66
> > 45.00	     0.54     	0.58
> > 40.00	     0.48	     0.48
> > 35.00	     0.42     	0.39
> > 30.00     	0.36	     0.32
> > 25.00     	0.29      0.27
> > 20.00	     0.24     	0.21
> > 15.00	     0.19	     0.17
> > 10.00      0.14      0.13
> > 5.00	      0.09	     0.09
> > 0.00	      0.05	     0.05

Jeff, 
Thanks for the math! Now here's the question, If Dmax = 1.8 and Dmin 
= 0.05 What percentage of the dynamic range is, say, .6? Can you 
show us how to do it?

Barry

--- In DigitalBlackandWhiteThePrint@y..., "iwasnvrhere" 
<iwasnvrhere@y...> wrote:
>     This might help. 
>  optical density (OD): For a given wavelength, an expression of 
the 
> transmittance of an optical element. Note 1: Optical density is 
> expressed by log10(1/T ) where T is transmittance. (188) Note 2: 
The 
> higher the optical density, the lower the transmittance. Note 3: 
> Optical density times 10 is equal to transmission loss expressed 
in 
> decibels, e.g. , an optical density of 0.3 corresponds to a 
> transmission loss of 3 dB. Def of optical density.
> 
> Jeff
> 
> 
> 
> 
> > John,
> > You are at the same point as I am. Well, actually I'm a little 
> > ahead. The density readings are log to the base 10 so dividing 
the 
> > Dmax by 2 will not give you the expected 50% reading. I am 
> currently 
> > trying to figure out the math.
> > I will let you know when I get there,
> > 
> > Barry
> > 
> > --- In DigitalBlackandWhiteThePrint@y..., John Chervinsky 
> > <chervinsky@d...> wrote:
> > > Hi,
> > > 
> > > I am attempting to calibrate my printer output using a 
calibrated 
> > X-Rite 810 densitometer.  I am using MIS FS inks through an 
Epson 
> > 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize 
> > that this question has come up in the past, but practical 
elements 
> > of technique were omitted.  Below you will find the reflective 
> > densitometer (visual) output vs a 21 step stepwedge.  I did 
> > measurements using both the Randall and Piezography workflows.  
If 
> > you look at the numbers carefully, you will conclude as to how 
> > shockingly non-linear they are.  I would have expected, for 
example 
> > that the 50 % reading would have been close to 1.7/2 = .85.  The 
> > Measured value of around 0.6 is WAY off!
> > > 
> > > Has anyone else had this experience? I would not think that my 
> > paper choice would have that much effect.  Are there subtle 
> > differences in using a reflective densitometer as opposed to a 
> > spectrophotometer to do the measurements? It would seem that for 
> > grayscale work that a densitometer should be fine.  Please 
advise.

> > > 
> > > Thanks!
> > > 
> > > -John Chervinsky
> > > 
> > > 
> > > 
> > > STEPWEDGE  CONE      RANDALL
> > > 100.0     	1.71     	1.77
> > > 95.00     	1.54     	1.66
> > > 90.00	     1.40     	1.57
> > > 85.00	     1.26     	1.45
> > > 80.00	     1.15     	1.33
> > > 75.00	     1.05	     1.20
> > > 70.00     	0.96     	1.07
> > > 65.00	     0.86     	0.95
> > > 60.00     	0.78	     0.83
> > > 55.00     	0.69      0.76
> > > 50.00	     0.61     	0.66
> > > 45.00	     0.54     	0.58
> > > 40.00	     0.48	     0.48
> > > 35.00	     0.42     	0.39
> > > 30.00     	0.36	     0.32
> > > 25.00     	0.29      0.27
> > > 20.00	     0.24     	0.21
> > > 15.00	     0.19	     0.17
> > > 10.00      0.14      0.13
> > > 5.00	      0.09	     0.09
> > > 0.00	      0.05	     0.05

Barry,

If dmax is 1.8 and dmin is 0.05 then the Density Range is 1.75.
To find what percentage of the Density Range .6 is divide .6/1.75=0.34 
or 34%

Mike

On Tuesday, April 23, 2002, at 08:31 PM, flyfishingusa2002 wrote:

> Jeff,
> Thanks for the math! Now here's the question, If Dmax = 1.8 and Dmin
> = 0.05 What percentage of the dynamic range is, say, .6? Can you
> show us how to do it?
>
> Barry
>
> --- In DigitalBlackandWhiteThePrint@y..., "iwasnvrhere"
> <iwasnvrhere@y...> wrote:
>>     This might help.
>>  optical density (OD): For a given wavelength, an expression of
> the
>> transmittance of an optical element. Note 1: Optical density is
>> expressed by log10(1/T ) where T is transmittance. (188) Note 2:
> The
>> higher the optical density, the lower the transmittance. Note 3:
>> Optical density times 10 is equal to transmission loss expressed
> in
>> decibels, e.g. , an optical density of 0.3 corresponds to a
>> transmission loss of 3 dB. Def of optical density.
>>
>> Jeff
>>
>>
>>
>>
>>> John,
>>> You are at the same point as I am. Well, actually I'm a little
>>> ahead. The density readings are log to the base 10 so dividing
> the
>>> Dmax by 2 will not give you the expected 50% reading. I am
>> currently
>>> trying to figure out the math.
>>> I will let you know when I get there,
>>>
>>> Barry
>>>
>>> --- In DigitalBlackandWhiteThePrint@y..., John Chervinsky
>>> <chervinsky@d...> wrote:
>>>> Hi,
>>>>
>>>> I am attempting to calibrate my printer output using a
> calibrated
>>> X-Rite 810 densitometer.  I am using MIS FS inks through an
> Epson
>>> 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize
>>> that this question has come up in the past, but practical
> elements
>>> of technique were omitted.  Below you will find the reflective
>>> densitometer (visual) output vs a 21 step stepwedge.  I did
>>> measurements using both the Randall and Piezography workflows.
> If
>>> you look at the numbers carefully, you will conclude as to how
>>> shockingly non-linear they are.  I would have expected, for
> example
>>> that the 50 % reading would have been close to 1.7/2 = .85.  The
>>> Measured value of around 0.6 is WAY off!
>>>>
>>>> Has anyone else had this experience? I would not think that my
>>> paper choice would have that much effect.  Are there subtle
>>> differences in using a reflective densitometer as opposed to a
>>> spectrophotometer to do the measurements? It would seem that for
>>> grayscale work that a densitometer should be fine.  Please
> advise.
>>>>
>>>> Thanks!
>>>>
>>>> -John Chervinsky
>>>>
>>>>
>>>>
>>>> STEPWEDGE  CONE      RANDALL
>>>> 100.0     	1.71     	1.77
>>>> 95.00     	1.54     	1.66
>>>> 90.00	     1.40     	1.57
>>>> 85.00	     1.26     	1.45
>>>> 80.00	     1.15     	1.33
>>>> 75.00	     1.05	     1.20
>>>> 70.00     	0.96     	1.07
>>>> 65.00	     0.86     	0.95
>>>> 60.00     	0.78	     0.83
>>>> 55.00     	0.69      0.76
>>>> 50.00	     0.61     	0.66
>>>> 45.00	     0.54     	0.58
>>>> 40.00	     0.48	     0.48
>>>> 35.00	     0.42     	0.39
>>>> 30.00     	0.36	     0.32
>>>> 25.00     	0.29      0.27
>>>> 20.00	     0.24     	0.21
>>>> 15.00	     0.19	     0.17
>>>> 10.00      0.14      0.13
>>>> 5.00	      0.09	     0.09
>>>> 0.00	      0.05	     0.05
>
>
>
> Please visit the Group Homepage to check the Files, Bookmarks, Polls 
> and other resources as they are often being updated. The page is at:
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>
>

Jeff...

When measuring paper, you are measuring reflection.  When measuring film,
you are measuring transmission.  I believe the discussion at hand was about
measuring paper, so if you substitute "reflect..." for "transmitt..." in
what you wrote below, I believe it'll fit the discussion.

Regards,

Austin

>     This might help.
>  optical density (OD): For a given wavelength, an expression of the
> transmittance of an optical element. Note 1: Optical density is
> expressed by log10(1/T ) where T is transmittance. (188) Note 2: The
> higher the optical density, the lower the transmittance. Note 3:
> Optical density times 10 is equal to transmission loss expressed in
> decibels, e.g. , an optical density of 0.3 corresponds to a
> transmission loss of 3 dB. Def of optical density.
>
> Jeff

You might want to take a look at the document, RGB Scanning Guide, by Don Hutcheson 
(available on his website http://www.hutchcolor.com or in the files section of Yahoo 
ScanHi-End).  On page 5 there's a table that shows typical values for RGB, Luminence and 
Density. The information is for transmissive readings but it illustrates the non-linear nature of the 
luminence/density relationship.  With overall density ranging from 0 to 4.0, medium gray 
translates into a density of about 0.7.

- Tom Dunn

--- In DigitalBlackandWhiteThePrint@y..., "chervinsky02144" <chervinsky@d...> wrote:

> Hi,
> 
> I am attempting to calibrate my printer output using a calibrated
> X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 1160
> onto PhotoRag 308 paper; I am on a Mac computer.  I realize that this
> question has come up in the past, but practical elements of technique
> were omitted.  Below you will find the reflective densitometer
> (visual) output vs a 21 step stepwedge.  I did measurements using both
> the Randall and Piezography workflows.  If you look at the numbers
> carefully, you will conclude as to how shockingly non-linear they are.
>  I would have expected, for example that the 50 % reading would have
> been close to 1.7/2 = .85.  The Measured value of around 0.6 is WAY
> off!
> 
> Has anyone else had this experience? I would not think that my paper
> choice would have that much effect.  Are there subtle differences in
> using a reflective densitometer as opposed to a spectrophotometer to
> do the measurements? It would seem that for grayscale work that a
> densitometer should be fine.  Please advise.
> 
> Thanks!
> 
> -John Chervinsky
> 
> 
> 
> STEPWEDGE  CONE      RANDALL
> 100.0     	1.71     	1.77
> 95.00     	1.54     	1.66
> 90.00           1.40     	1.57
> 85.00           1.26     	1.45
> 80.00           1.15     	1.33
> 75.00           1.05	        1.20
> 70.00     	0.96     	1.07
> 65.00           0.86     	0.95
> 60.00     	0.78	        0.83
> 55.00     	0.69            0.76
> 50.00           0.61     	0.66
> 45.00           0.54     	0.58
> 40.00           0.48	        0.48
> 35.00           0.42     	0.39
> 30.00     	0.36	        0.32
> 25.00     	0.29            0.27
> 20.00           0.24     	0.21
> 15.00           0.19	        0.17
> 10.00           0.14            0.13
> 5.00            0.09	        0.09
> 0.00            0.05	        0.05

[Mahesi Caplan-Faust] I am trying to print A4's using cone inks on a new
1280 and I am getting heavy indentations. Has anyone had a similir
experience. Epson say I must use Epson papers but I have been printing on
Photo rag and do not want to change.

Adam

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----- Original Message -----

From: "flyfishingusa2002" <tflyfish@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, April 24, 2002 12:23 AM
Subject: [Digital BW] Re: Densitometry Help


> John,
> You are at the same point as I am. Well, actually I'm a little
> ahead. The density readings are log to the base 10 so dividing the
> Dmax by 2 will not give you the expected 50% reading. I am currently
> trying to figure out the math.
> I will let you know when I get there,

Every 0.30 is double or half the previous reading thus if 0.0 density = 100%
transmission (you should be so lucky) - 0.3 density =50% - 0.6 = 25% - 0.9 =
12.3% which is why 1.0 = 10% - 2.0 = 1%  (i.e.100-1 ratio) 3.0 = 0.1% (i.e.
1000-1 ratio) and on and on.

If you work in % numbers just use a set of log tables to the power of two to
find the density numbers.

A 1.7 log density for a four colour image using a good paper printed off-set
lithography would be considered about average.

A good coated art paper or if you like a glossy photographic image would
give a density of around 2.0 give or take a point which, |I might add, is
about the highest density you are likely to achieve.

Thanks Mike, Did that answer your question Barry? Oh and the switch 
to Reflectance from Transmittance is a good piont- I just copied the 
definition for the math. 

Jeff.

> Barry,
> 
> If dmax is 1.8 and dmin is 0.05 then the Density Range is 1.75.
> To find what percentage of the Density Range .6 is 
divide .6/1.75=0.34 
> or 34%
> 
> Mike
> 
> On Tuesday, April 23, 2002, at 08:31 PM, flyfishingusa2002 wrote:
> 
> > Jeff,
> > Thanks for the math! Now here's the question, If Dmax = 1.8 and 
Dmin
> > = 0.05 What percentage of the dynamic range is, say, .6? Can you
> > show us how to do it?
> >
> > Barry
> >
> > --- In DigitalBlackandWhiteThePrint@y..., "iwasnvrhere"
> > <iwasnvrhere@y...> wrote:
> >>     This might help.
> >>  optical density (OD): For a given wavelength, an expression of
> > the
> >> transmittance of an optical element. Note 1: Optical density is
> >> expressed by log10(1/T ) where T is transmittance. (188) Note 2:
> > The
> >> higher the optical density, the lower the transmittance. Note 3:
> >> Optical density times 10 is equal to transmission loss expressed
> > in
> >> decibels, e.g. , an optical density of 0.3 corresponds to a
> >> transmission loss of 3 dB. Def of optical density.
> >>
> >> Jeff
> >>
> >>
> >>
> >>
> >>> John,
> >>> You are at the same point as I am. Well, actually I'm a little
> >>> ahead. The density readings are log to the base 10 so dividing
> > the
> >>> Dmax by 2 will not give you the expected 50% reading. I am
> >> currently
> >>> trying to figure out the math.
> >>> I will let you know when I get there,
> >>>
> >>> Barry
> >>>
> >>> --- In DigitalBlackandWhiteThePrint@y..., John Chervinsky
> >>> <chervinsky@d...> wrote:
> >>>> Hi,
> >>>>
> >>>> I am attempting to calibrate my printer output using a
> > calibrated
> >>> X-Rite 810 densitometer.  I am using MIS FS inks through an
> > Epson
> >>> 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize
> >>> that this question has come up in the past, but practical
> > elements
> >>> of technique were omitted.  Below you will find the reflective
> >>> densitometer (visual) output vs a 21 step stepwedge.  I did
> >>> measurements using both the Randall and Piezography workflows.
> > If
> >>> you look at the numbers carefully, you will conclude as to how
> >>> shockingly non-linear they are.  I would have expected, for
> > example
> >>> that the 50 % reading would have been close to 1.7/2 = .85.  The
> >>> Measured value of around 0.6 is WAY off!
> >>>>
> >>>> Has anyone else had this experience? I would not think that my
> >>> paper choice would have that much effect.  Are there subtle
> >>> differences in using a reflective densitometer as opposed to a
> >>> spectrophotometer to do the measurements? It would seem that for
> >>> grayscale work that a densitometer should be fine.  Please
> > advise.
> >>>>
> >>>> Thanks!
> >>>>
> >>>> -John Chervinsky
> >>>>
> >>>>
> >>>>
> >>>> STEPWEDGE  CONE      RANDALL
> >>>> 100.0     	1.71     	1.77
> >>>> 95.00     	1.54     	1.66
> >>>> 90.00	     1.40     	1.57
> >>>> 85.00	     1.26     	1.45
> >>>> 80.00	     1.15     	1.33
> >>>> 75.00	     1.05	     1.20
> >>>> 70.00     	0.96     	1.07
> >>>> 65.00	     0.86     	0.95
> >>>> 60.00     	0.78	     0.83
> >>>> 55.00     	0.69      0.76
> >>>> 50.00	     0.61     	0.66
> >>>> 45.00	     0.54     	0.58
> >>>> 40.00	     0.48	     0.48
> >>>> 35.00	     0.42     	0.39
> >>>> 30.00     	0.36	     0.32
> >>>> 25.00     	0.29      0.27
> >>>> 20.00	     0.24     	0.21
> >>>> 15.00	     0.19	     0.17
> >>>> 10.00      0.14      0.13
> >>>> 5.00	      0.09	     0.09
> >>>> 0.00	      0.05	     0.05
> >
> >
> >
> > Please visit the Group Homepage to check the Files, Bookmarks, 
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Huh! (hits on the brakes, tires squeeling, pulls to the side of 
the road) Um, let's take two steps back here and let me ask this just 
to make sure were all talking about the same thing here. Are you 
trying to find the relationship between the % values on the stepwedge 
with OD measurements? If you are there is absolutely no relationship. 
The % marks are the K values for the Photoshop color picker. Use the 
dropper and pick a spot. If you click on the little window at the 
bottom of the tool bar the picker will come up. In it are the color 
space values and a CMYK % bar. That's what the % values are on the 
step wedge-the K value. This is what the system thinks should be laid 
down to hit that color or in our case density. 

 Paul reported getting close values with a one ink setup and that is 
because the printer would print 50% coverage with one ink(or use CMY)-
 but there's either lots of big dots or a process grey. The quads use 
4 inks (duh) and the plug in tells the printer a whole different 
command for a density target. i.e. Instead of printing 50% coverage 
of a max density ink it would print 100% coverage of a 50% diluted 
ink. This eliminates dots and allow for the smooth transitions 
between densities, the whole point of the quad system. Does that help?

Jeff.


> Hi,
> 
> I am attempting to calibrate my printer output using a calibrated
> X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 
1160
> onto PhotoRag 308 paper; I am on a Mac computer.  I realize that 
this
> question has come up in the past, but practical elements of 
technique
> were omitted.  Below you will find the reflective densitometer
> (visual) output vs a 21 step stepwedge.  I did measurements using 
both
> the Randall and Piezography workflows.  If you look at the numbers
> carefully, you will conclude as to how shockingly non-linear they 
are.

>  I would have expected, for example that the 50 % reading would have
> been close to 1.7/2 = .85.  The Measured value of around 0.6 is WAY
> off!
> 
> Has anyone else had this experience? I would not think that my paper
> choice would have that much effect.  Are there subtle differences in
> using a reflective densitometer as opposed to a spectrophotometer to
> do the measurements? It would seem that for grayscale work that a
> densitometer should be fine.  Please advise.
> 
> Thanks!
> 
> -John Chervinsky
> 
> 
> 
> STEPWEDGE  CONE      RANDALL
> 100.0     	1.71     	1.77
> 95.00     	1.54     	1.66
> 90.00           1.40     	1.57
> 85.00           1.26     	1.45
> 80.00           1.15     	1.33
> 75.00           1.05	        1.20
> 70.00     	0.96     	1.07
> 65.00           0.86     	0.95
> 60.00     	0.78	        0.83
> 55.00     	0.69            0.76
> 50.00           0.61     	0.66
> 45.00           0.54     	0.58
> 40.00           0.48	        0.48
> 35.00           0.42     	0.39
> 30.00     	0.36	        0.32
> 25.00     	0.29            0.27
> 20.00           0.24     	0.21
> 15.00           0.19	        0.17
> 10.00           0.14            0.13
> 5.00            0.09	        0.09
> 0.00            0.05	        0.05

--- In DigitalBlackandWhiteThePrint@y..., "iwasnvrhere"
<iwasnvrhere@y...> wrote:
>    Huh! (hits on the brakes, tires squeeling, pulls to the side of 
> the road) Um, let's take two steps back here and let me ask this just 
> to make sure were all talking about the same thing here. Are you 
> trying to find the relationship between the % values on the stepwedge 
> with OD measurements? If you are there is absolutely no relationship. 


I am beginning to find this out the hard way.  The mathematical
relationships posted thus far do not make sense to me.  Actually,
there is a relationship between the photoshop eyedropper and
reflective densitometer output, we just do not know what it is.  All
of this is leading to Paul's practical method of using a "standard" to
calibrate the densitometer.  If anyone else has any other ideas, I
would sure be glad to hear about it.

Thanks!

-John

> >    Huh! (hits on the brakes, tires squeeling, pulls to the side 
of 
> > the road) Um, let's take two steps back here and let me ask this 
just 
> > to make sure were all talking about the same thing here. Are you 
> > trying to find the relationship between the % values on the 
stepwedge 
> > with OD measurements? If you are there is absolutely no 
relationship. 
> 
> 
> I am beginning to find this out the hard way.  The mathematical
> relationships posted thus far do not make sense to me.  Actually,
> there is a relationship between the photoshop eyedropper and
> reflective densitometer output, we just do not know what it is.  

   Well yes there is the obvious relationship that at the stepwedges %
X you get density Y. But the % value listed on the stepwedge isn't 
the relation it seems to be. That's creating the confusion people 
have been posting. At 50% on the stepwedge people were expecting 50% 
of the max density but it doesn't work that way. 


Jeff

On Tue, Apr 23, 2002 at 05:45:05PM -0400, John Chervinsky wrote:
> I am attempting to calibrate my printer output using a calibrated X-Rite 810 densitometer.  I am using MIS FS inks through an Epson 1160 onto PhotoRag 308 paper; I am on a Mac computer.  I realize that this question has come up in the past, but practical elements of technique were omitted.  Below you will find the reflective densitometer (visual) output vs a 21 step stepwedge.  I did measurements using both the Randall and Piezography workflows.  If you look at the numbers carefully, you will conclude as to how shockingly non-linear they are.  I would have expected, for example that the 50 % reading would have been close to 1.7/2 = .85.  The Measured value of around 0.6 is WAY off!
> 
> STEPWEDGE  CONE      RANDALL
> 50.00	     0.61     	0.66
> 

The density numbers are just about right if we are distributing the data
according to human perception. If we say that we percieve a middle tone as
18% (as in a standard grey card) to 22% reflectance then this equates to 
densities of 0.74 and 0.66 respectively. This then is simlar to the results 
you are getting when doing your actual measurements.

I think where you (and indeed I until I thought about it more) are going
astray is in thinking of 50% as a middle between maximum and minimum
densities rather than just a standard deviation from minimum density.
Doesn't the eye always seek a white point and adjust from there?

-- 
Tony Terlecki
ajt@...
Running Debian/GNU 2.2 Linux

Adam,

Based on an e-mail exchange we had I checked my prints and I believe 
I have the same indentation characteristic you are speaking of.

For others who may not know, what Adam is talking about is a set of 
parallel lines of indentation that appear to be caused by the pizza 
wheels.  We are not talking about the pin pricks caused by the pizza 
wheel teeth.  Rather, it is a deformation of the paper that could be 
explained by the pressure of the pizza wheels pressing down hard on 
paper that is wet with ink and deforming it.

I noticed the same thing on my 1280 printer.  However, it is only 
visible (to me) if you look on the backside of the paper.  I do not 
notice it on the front side of the paper.  The print appears to 
disguise the indentations.

I think I am on the right track when I say that it is caused by the 
wet paper.  On the back side of the paper I only see the indentations 
across the area of the paper occupied by the print itself.

I do not recall seeing this with the 1200 printer.  My question is 
this.  Are the Cone profiles laying down too much ink on the 1280 
printers?  I am using EAM paper, MIS inks, Piezo driver with EAM 
profile printed in "Best" quality.  Note that Adam's situation is 
Cone Inks, Piezo driver, and some other paper.

I have also checked this out on some contact sheets printed 
in "Better" quality mode.  The indentations seem far less 
pronounced.  So, does anyone have any comments on this "feature" of 
the 1280 printer?  From what I understand Adam is fixing the problem 
with lightly wetting the back of the print and ironing them dry.

Regards,
Mike

--- In DigitalBlackandWhiteThePrint@y..., "Mahesi Caplan-Faust" 
<caplan@n...> wrote:
> [Mahesi Caplan-Faust] I am trying to print A4's using cone inks on 
a new
> 1280 and I am getting heavy indentations. Has anyone had a similir
> experience. Epson say I must use Epson papers but I have been 
printing on
> Photo rag and do not want to change.
> 
> Adam
> 
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