[argyllcms] Re: Profile -r option

Thanks for that...very timely!

As it happens I am using a Wolf Faust IT8 target, and my scanner is a Minolta Multipro (dedicated film scanner).

I'm not sure if I have the time to run all the profilers myself, but I'd be happy to scan the special target that was being discussed and send the data somewhere. Who should I register interest with?

Cheers,
Milt

Gerhard Fuernkranz wrote: 

Milton,

since you obviously own a good film scanner, you might be a possible candidate for the following evaluation offered by Wolf Faust (the famous maker of IT8 targets):

http://sourceforge.net/mailarchive/forum.php?thread_id=10074837&forum_id=1912


This would give you the opportunity to find out, how good your profiles really perform (and also the opportunity to find the optimal smoothness trade-off).

Btw, Wolf Faust also seems to be rather sceptical when he sees "user reports from argyll CMS users with mean dE <0.35 on batch average slide film targets".

Best Regards,
Gerhard


Milton Taylor wrote: 
Hi Gerhard,

OK I understand, and I see the difficulty in making a call on this.

In this case the target scan is from a 35mm IT8 transmissive target scanned at 1600dpi. So the end result is that each patch on the IT8 has about 50x50 useful pixels in it. I'm not sure what scanin's sampling algorithm is, i.e. every pixel or just intermediate ones. If it samples and averages all of them, then that's 2500 samples per patch, so I would expect that noise and related imperfections in the patch would would have been virtually eliminated. (The scanner does multisampling to get rid of CCD noise too).

My scanner is fitted with a 'Scanhancer' lamp diffuser, which quite possibly introduces some spectral characteristics that don't follow a standard polynomial or gamma-curve TRC. That's why I would have tended toward a tighter fit LUT profile than a nice smooth polynomial curve.

Of course, there are also going to be measurement errors in the original target reference data, but I don't have a feel for how large those are.

Reproduceability: well, I would be disappointed in the scanner if it was introducing errors of up to dE of 4 from one scan to the next of the same slide. I really think the scanner is much better than that.

So my gut feel would be to run with the lower -r, perhaps 0.5.

Cheers...


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