> In order to compare to the target reference file, you actually need to use
> "-t 3" (i.e. absolute colorimetric).
 
Thank you Gerhard, for your help!
 
But the real problem is not the conversion to connection space (this is already quite good), it’s the conversion to sRGB, where I get huge errors, using command:
 
-        icctrans -I <custom profile> -o "sRGB Color Space Profile.icm" -t <color intent> <measurement_file>
 
It does not seem to make much difference, which rendering intent I use, the error remains on a high level.
 
I actually noticed, that I get much better results, when first converting to Lab with:
 
-        icctrans  -i <custom profile> -o *Lab -t 3 <measurement_file>
 
and then converting from there to sRGB with a different rendering intent (Perceptual):
 
- icctrans -I *Lab -o "sRGB Color Space Profile.icm" -t 0
 
 
I figured out that the problem arises again, if I use rendering intent absolute colorimetric (-t 3) in the last transformation.
 
I do not really understand, why an absolute colorimetric rendering intent leads to such an error.
 
Is there any way to use two different rendering intents for both parts of the color transformation (input and output profile) without using two separate transformations, as this may slow down runtime performance? 
 
 
Best regards,
Dietmar