Is there a program available that can determine, with reasonable accuracy, dot gain based on Lab or spectral data?
The program should be able to determine dot gain for process and non-process colors.
You need density measurements to use the Murray-Davies equation… You can estimate the gain in C, M, Y or K with XYZ reflectance values.
For dot gain from Lab* measurements, check out the calculator section of Bruce Lindbloom’s website at brucelindbloom.com/
The one you’re looking for is at the very bottom, “Dot Gain from Lab or Profile.”
You cannot get gain for spot colors using this method, as reflectance values differ from standard CMY inks.
If you can take density measurements, use the Dot Gain Calculator which utilizes the Murray Davies equation. Use the visual density value for non-process inks.
There are also spreadsheets on Bruce’s site to calculate density (among other things) from spectral data. From there you could throw in the Murray-Davies equation to calculate dotgain. You can also get density measurements from Spectral data within MeasureTool if, for example, your using an EyeOne.
You could also build your own spread sheet, applying the Murray-Davies formula to density data. If you have an X-rite instrument and Toolcrib, you can set it up so density measurements pop into Excel where the dot gain values automatically update. This works great for process, but I can’t comment on spots.
There are some programs that do all this for you, like ColorMetrix for example as part of their quality control packages, but if your looking for a cheap solution, it requires a little work.
Thank you Brian and Michael for your informative responses.
Brian, when you refer to “visual density values,” is this the same as the “special density” value that I can choose within the PM Pro Measure Tool/Spot measurement?
If your software allows a custom filter set (or custom calculation with standard filters) that better describes the density of a spot color, then it’s likely those calculations would be more accurate. I’m speculating that the “special density” you refer to is this function. I do not know what “PM Pro” is.
With a standard reflectance densitometer, you can get density readings through a Red, Green or Blue filter. (For Cyan, Magenta and Yellow readings, respectively) Also, a third reading is derived from the other three, used to measure black and spot colors. That density is referred to as “visual” by the X-Rite instruments I use.
Thanks, Brian.
According to the ProfileMaker Pro help file, the “special” reading is defined as:
“Special: Special uses a mathematical filter that is oriented to the current maximum density of the measured color and so does not correspond to any standard filter.”
This kinda sorta sounds like the same animal - yes?
“Special” does not equal “Visual”. Choosing K for your color channel gives you the same measurement you would get from a visual density measurement of a standard densitometer, but perhaps the Special option will give you a more precise reading for spot color. 
I don’t know how you would verify that though, and I’m assuming that Pantone would simply recommend using the visual density, as it’s more readily available to most folk’s.
Yep.
I recall having a Gretag Macbeth instrument that would read a spot color with all the filters, derive some custom filter (mathematical filter) and then add that to the color list… it would show up with C, M, Y as CUSTOM and if you wanted to do calculations (dot gain, match, density) you could select that as the color. (If I remember correctly it would even auto-select that color if it was different enough from the other primaries)
In any case, using this setting would likely yield higher accuracy than using visual density alone. (especialy if it’s a color close to another primary or very light in color)
Christopher: “Same animal?”
Mike: “No.”
Me: “Yes.”
Christopher: “Wha…?”
Michael is right, special does not equal visual… I hope I made that clear in my post!
Okay, then…
Steve, Would you weigh in on this one, please?
Now that I’ve taken time to actually work with the Measure Tool “special” measurement function, I am sure that this is PM Pro’s designation for the visual density animal.
Why in the world they decided to not call it “visual” density is beyond me… (unless, of course, over in Europe this particular density value would always ride the short-bus to school )
Hmmm…your conclusions are different than mine. For example, If I measure the density of Pantone Reflex Blue C on an X-Rite 939, I get a density of V 1.71. Measuring that same patch with an i1 in MeasureTool, ANSI T with the Special color channel, I get a density of 2.29 along with the nanometer value. If I change the color channel to K and take a measurement, I get a density of 1.66, much closer to my original 1.71 density with the X-Rite instrument. I’ve tried this with a number of spot colors and get similar results.
Only recently has the ability to customize filter settings in order to create custom calculations been an option. For years, X-Rite has called the K channel reading “V” for visual.
It would be a mistake to change the symantics now… that visual density isn’t necessarily K only, but definitely isn’t suitable for all colors.
Suffice it to say that the “Special Density” function is definitely the best choice for measuring spot colors. A useable range of 0.0 to over 2.0 is much better in terms of making calculations, even if that number doesn’t necessarily correspond to a visual stimulus that we’re used to seeing.