Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: MirekElsner on June 17, 2010, 03:55:05 pm
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I feel bad about asking this question, because I am sure it was discussed before, either here or elsewhere. I could not find anything, though.
Is it possible to use ColorMunki to measure Dmax of a print? ColorMunki can read patch values in LAB. Is there any way to convert that to density?
Thanks!
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Go to Bruce Lindbloom's site http://www.brucelindbloom.com/ (http://www.brucelindbloom.com/), and choose the Companding Calculator under "Calcs."
This will let you convert L into density, which will give you Dmax.
Don't feel bad! If you couldn't find this info, there must be dozens of others looking for it too, and we just answered the question for them.
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A quick search gave me this:
What is the mathematical equation to convert Lab or XYZ to Density? (758)
I'm sorry, there isn't a direct conversion from CIELAB or XYZ to density. CIELAB and XYZ are based on visual color responses, while densitometers are designed to measure material properties (ink or dye amounts) of various systems.
from "Ask a Color Scientist!" by the "Munsell Color Science Laboratory" http://www.cis.rit.edu/mcsl/faq/#758 (http://www.cis.rit.edu/mcsl/faq/#758)
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Go to Bruce Lindbloom's site http://www.brucelindbloom.com/ (http://www.brucelindbloom.com/), and choose the Companding Calculator under "Calcs."
This will let you convert L into density, which will give you Dmax.
Don't feel bad! If you couldn't find this info, there must be dozens of others looking for it too, and we just answered the question for them.
Thanks Patrick. I wonder what formula is used for that. Do you happen to know?
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A quick search gave me this:
from "Ask a Color Scientist!" by the "Munsell Color Science Laboratory" http://www.cis.rit.edu/mcsl/faq/#758 (http://www.cis.rit.edu/mcsl/faq/#758)
Thanks. There may not be an equation, but apparently there is a way to convert
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Thanks Patrick. I wonder what formula is used for that. Do you happen to know?
http://www.digitalcolour.org/understanding/Density.htm (http://www.digitalcolour.org/understanding/Density.htm)
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Dmax is a measure of density. There are multiple formulas for calculating density and should be calculated from a spectral measurement. You can also calculate "colorimetric" density using the XYZ values of a color, although this value will not agree with DMAX measured from a traditional densitometer. Comparing Dmax values is much less meaningful than comparing L*a*b* values. If you really want to know send me the value as a CXF/CGATS file I can tell you the visual density value with my software.
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Thanks for the links and for pointing out the difference between colorimetric and visual density. I am now able to read cxf files generated by ColorMunki (that contains raw reflectance data for various wavelengths) and calculate visual density. The numbers are close to Bruce Lindbloom's calculator, even though I calculate it using reflectance and visual response and Bruce's calculator works from Lab. Perhaps because I'm looking at Dmax and Dmin, that are more or less gray values and the visual response does not matter so much here...
Why am I looking for Dmax? I was curious how my densities compare to traditional wet darkroom prints and I thought it would be easier to find Dmax numbers for those than Lab as the labs and producers used to measure it with densitometers.
Now I can go to the print forum and ask about typical densities. Thanks for help everyone!
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http://www.digitalcolour.org/understanding/Density.htm (http://www.digitalcolour.org/understanding/Density.htm)
Can anyone share the density.xls spreadsheet (L to visual density) because the site seems to be down.
I have Bruce spectral to visual density, and was looking for just L to density, patches are only gray.
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I am now able to read cxf files generated by ColorMunki (that contains raw reflectance data for various wavelengths)...
Could I ask for a pointer to software that can do it? Is Argyll capable of that?
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Could I ask for a pointer to software that can do it? Is Argyll capable of that?
Yes, Argyll will do that. Before I upgraded to an i1pro, I used a Munki for that exact purpose.
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Conversely, does anybody know how to convert from density to L*? I've read a Stouffer gray scale (T4110) with my transmission densitometer and would like to convert the density values to L*.
This page comes closer:
http://stonerosephotos.com/blog/2012/01/ink-density-reflectance-and-l/
But I can't make sense of the math (skipped that day in school)....he makes it sound obvious but it's not obvious to me. I'm interested in putting the formula into Excel or Numbers.
Terry
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Why am I looking for Dmax? I was curious how my densities compare to traditional wet darkroom prints and I thought it would be easier to find Dmax numbers for those than Lab as the labs and producers used to measure it with densitometers.
Now I can go to the print forum and ask about typical densities. Thanks for help everyone!
In my past life as a prepress tech for the screen printing industry, I had to use a Stouffer stepwedge to calculate development time in the darkroom for color seps, reproducing logos from business cards, processing continous tone B&W photos into 80-100 lpi line conversions so they'ld print beautifully on fabric and plastic.
Seeing it was dark in the darkroom I couldn't use my eyes to judge when to stop development so I had to rely on the Stouffer wedge to show step 5 before it went black where the rest of the wedge below 5 looked completely black. Switching to the light table to judge proper exposure I could now see all the 20 or so steps that I couldn't in the darkroom.
Why is "Grandpa Graphic" relating this to you? Because you folks are trying to determine making pictures by the numbers (for accuracy, consistency?) with no consideration to changing luminance levels as demonstrated in my "darkroom to light table" demo.
Numbers are a guide, not empirical evidence that you are coming up with a sure fire way for developing a process reproducing reality in a print with any consistency and precision.
Your curiosity will be satisfied of course but you won't be able to use any of the data on a consistent basis because a print looks best when you look at it under the same light not as a densitometer sees it which isn't the same as our eyes perceive density.
IOW you haven't factored in the luminance level the print's density will be viewed so the numbers become meaningless.
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Last time I was able to convert using Bruce xls file spectral to visual density, but this time I have only LAB data.
Perhaps somebody had the mentioned density file that converts L to density line Bruce companding calculator does?
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A quick search gave me this:
from "Ask a Color Scientist!" by the "Munsell Color Science Laboratory" http://www.cis.rit.edu/mcsl/faq/#758 (http://www.cis.rit.edu/mcsl/faq/#758)
There are a number of software products that do this from spectral data (MeasureTool, ColorAnt,BabelColor_CT&A). Not sure how Bruce came up with his method doing it from Lab. BabelColor_CT&A's Help document has a slew of information about all this: http://www.babelcolor.com/#CTandA
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Is it possible to use ColorMunki to measure Dmax of a print? ColorMunki can read patch values in LAB. Is there any way to convert that to density?
By using X-Rite ColorPicker,
if you are able to extract the reflectance data from a CxF exported file,
you can put them in a spreadsheet and get a very good visual density value estimation for the blacks by doing a simple calculation as follows:
=ABS(LOG(AVERAGE(A1:AJ1),10))
(assuming the reflectance data is a row from A1 to AJ1, as could be for a 380-730nm data set using 10nm steps).
You will see that, if the tone is reasonably neutral, the results will be very close to the ones you can get using the LindBloom "SpectralCalculator10nm.xls" spreadsheet.
If you get the reflectance data from Argyll chartread,
be sure to scale the values down by dividing it by 100 before doing the same above math
and pay attention to avoid the use of -H (hires) option.
I hope this could be useful.
Ciao.
Andrea :)
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There are a number of software products that do this from spectral data (MeasureTool, ColorAnt,BabelColor_CT&A). Not sure how Bruce came up with his method doing it from Lab. BabelColor_CT&A's Help document has a slew of information about all this: http://www.babelcolor.com/#CTandA
But how to do this from L values only?
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Thanks Patrick. I wonder what formula is used for that. Do you happen to know?
I think this boils down to the differences between radiometry and photometry. See this link (http://fp.optics.arizona.edu/Palmer/rpfaq/rpfaq.htm#radiometry). To quote from the article,
"Radiometry is the measurement of optical radiation, which is electromagnetic radiation within the frequency range between 3×10^11 and 3×10^16 Hz. This range corresponds to wavelengths between 0.01 and 1000 micrometres (m m), and includes the regions commonly called the ultraviolet, the visible and the infrared. Two out of many typical units encountered are watts/m2 and photons/sec-steradian. ...Photometry is just like radiometry except that everything is weighted by the spectral response of the eye."
Bill
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Very old thread, but since I stumbled upon it when searching for the answer I can add it here:
With argyll use spotread. Read the paper white note the Y in XYZ (Yw), then read a printed black patch and note the Y (Yb), then Dmax is -log10(Yb/Yw). Using a Colormunki my Hahnemuhle Photo Rag Pearl sample in front of me yielded -log10(0.348/93.067) = 2.43
If you don't have a scientific calculator at hand, you can use http://web2.0calc.com/ for example.
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With argyll use spotread. Read the paper white note the Y in XYZ (Yw), then read a printed black patch and note the Y (Yb), then Dmax is -log10(Yb/Yw). Using a Colormunki my Hahnemuhle Photo Rag Pearl sample in front of me yielded -log10(0.348/93.067) = 2.43
ArgyllPRO ColorMeter will give you this directly from the ColorMunki measurement too - see http://www.argyllcms.com/pro/cmdoc/readout_config.html#Densities.