[argyllcms] Re: Use of calibrated display to profile digital camera

On Saturday 26 July 2008 02:14:40 pm Milan Knížek wrote:
> Hi all!
>
> I am aware that it is not usually recommended to use IT8 targets for
> preparation of ICC camera profiles for colour rendering of real scenes.
> Since one of the reasons is smaller gamut of IT8, 

No target gamut is really not a significant issue with these targets.  
Reflective IT8.7 targets have a dynamic range of about 7 stops (actually a 
little more than this) which is close to what most digital cameras are capable 
of producing.  The real issue with IT8 targets and other targets that use 
photographic paper like the HCT target is that the spectral characteristics of 
the target can be different than real world objects and this can cause 
problems in some lighting conditions.  This issue tends to only become 
significant under lighting conditions that have spectral charaterisics that 
are not smooth.  For example florecent lights tend to have large spikes and 
drops outs in the spectral distribution and this can cause issues for photo 
paper based targets.  But at least under lights that have smooth spectral 
characterisics (sun light, incandesent light  and strobes) you will be hard 
pressed to find sigificant issues with the resulting profiles related to this 
issue.  In other words unless you work under floresent lights or other types 
of lights with unsmooth spectral characterisics you will be fine with profiles 
created using a good IT8.7 target assuming that other aspects of your work 
flow are OK.

If you are concerned about spectral effects of the target one option is to use 
a target that is based on some other reproduction method that is designed to 
have more natural spectral characteristics.  For example there are the very 
expensive X-Rite/GretagMacbeth targets (around $300) or the less expensive 
DigitaL TargeT 003.  I have not used any of the X-Rite/GretagMacbeth targets 
but I do have a DigitaL TargeT 003 and I have been pleased with the results.  
These targets are hand measured and cost aprox. $100 including shipping for a 
letter size target.  These are intended specifically for profiling of digital 
cameras.  Considering that these are hand measured the price is very 
reasonable.

> I thought about use of
> a calibrated and profiled display (supporting near to Adobe RGB colour
> space). I did some research with Google and found that this is already
> patented in the USA: http://www.patentstorm.us/patents/6654493.html
>
> Have anyone tried to use calibrated and profiled display to create a
> profile for digital camera and got good results? Would it make sense
> considering low-end display calibration tools (Eye One II, Huey)?

You might have issues related to spectral charaterisics of the target which is 
dicated by the monitors primaries and which will be different for different 
monitors.  In addition the target in this case would not be a reflective 
target which is what the device you are profiling is designed to capture.  I 
would be inclined to think this will not work very well.

>
> P.S. At the moment, I use ICC profile in UFRaw (linux) based on IT8
> target, since it usually gives me better results than other alternatives
> (no profile, colour matrix, profiles from RAW converter by Canon).
>
> Best regards,
>
> Milan Knizek
> knizek (dot) confy (at) volny (dot) cz
> http://www.milan-knizek.net - about linux and photography

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