[argyllcms] Re: Determining proper error value for -r

> -------- Original-Nachricht --------
> Datum: Wed, 24 May 2006 11:02:51 +1000
> Von: Graeme Gill <graeme@xxxxxxxxxxxxx>
>
> > Like I said, I used 39 test patches from an Argyll 39-patch chart,
> > with eight copies of each patch.
>
> OK, seems pretty reasonable then.

Except probably, that a sample size of 8 per color is rather very small to 
estimate the population variance by the sample variance reliably. I have done 
basicallly the same experiment some time ago (also with about 50 patches and 10 
replications each) in order to get an estimate of the reproducibility of my 
laser printer. Basically there is a trend in evidence that some colors are 
reproduced with a lower and others with a larger variance, however one must be 
very careful judging this, since for such a small sample size, a difference 
between say 1.8dE and 2dE is statistically not really significant; i.e. the 
color with 1.8dE sample standard deviation and the other color with the 2dE 
sample standard deviation could very likely also be just two different samples 
from the same population, or the color with the 1.8 dE sample standard 
deviation could even come from a population with a larger population standard 
deviation then the color with the 2dE sample standard deviation.

I'm in fact wondering whether it might be worth to attempt to fit a very smooth 
RGB/CMYK -> variance RSPL mapping to this data, and to use this RSPL during 
profile generation to obtain an individual weight for each training set data 
point (i.e. weight[i]=1/variance[i], probably normalized such that the sum of 
the weights is 1.0 in order that the per data point weights do not interfere to 
much with the existing avgdev -> raw smoothness mapping).

Regards,
Gerhard

> The real overhead is in making
> several separate prints to exercise that source of error.

-- 
Gerhard Fuernkranz
nospam456@xxxxxx

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