[argyllcms] Characterizing a scanner using Argyll

Off and on for the past year or so I have been attempting to characterize a 
scanner using ICC profiles so that it can be used to acquire accurate Lab color 
measurements. The scanner is mainly used to analyze pages that come from laser 
printers although some inkjet printers have been used. The most common way that 
I have read to characterize a scanner is by using a target like the Q60, but 
because of the fact that I want to analyze printed output, as opposed to 
photos, I found that using an Argyll-generated target (using targen and 
printtarg) produces better results because the target matches the type of media 
that I want to  measure. Additionally, I usually modify the color values on the 
patches to include significantly more pure colors because I am predominantly 
measuring a printers ability to uniformly print pure colors (CMYK) on a page. 

When measuring the error involved in a measurement I calculate the delta E 
(1976) between the value that comes from the ICC profile and the value that 
comes from the Gretag Spectrolino. The results vary based upon several factors, 
the most important of which seems to be the gamut of the printer that was used 
to create the profile. For example, if I create a profile using pages from a 
printer and then use the ICC profile to measure pages that were printed on the 
same printer, the average delta E value when compared to the Gretag Spectrolino 
is consistently under 2. However, if I measure pages using a printer that has a 
larger gamut than the one used to create the profile, then the out-of-gamut 
colors tend to produce extremely large max delta E value ranging anywhere up to 
100 depending on the printers used. 

Is there any way to increase the accuracy of the profile when faced with 
out-of-gamut colors?

When I create the profile from a ti3 file I generally use the following command:
colprof -v -qh -u -al <base_name>

There are several options that the colprof function provides that I am not 
utilizing. Do you have any suggestions for options that I should use that might 
help alleviate this problem? I have tried several combinations but my lack of 
expertise on the subject matter seems to make it more of a guessing game than 
anything else. 

Any comments, suggestions, or criticisms would be greatly appreciated, 

Andrew

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