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Re: filmscanners: Vuescan: "device RGB"



On Wed, 28 Mar 2001 17:20:11 -0800  shAf (michael@shaffer.net) wrote:

> ... Tony seems to be
> under the impression, for those scanners which have been chracterized,
> Vuescan will transform the scanned RGB data into "device RGB".  

The raw scan is in an unspecified device space, scanner RGB. Ed's transform, 
applied during the production of the Crop file, munges that against his 
characterisation and the result is a scan with altered data values within 
Vuescan's working space (which I previously said I thought was maybe sRGB, but 
as has been pointed out it ain't, it's Kodak's PCD space - too many facts, too 
little brain:). 

This isn't classical ICC-type colour management (=don't change the data, just 
append a tag which provides a map for interpretation of device colour). Vuescan 
does change the data, so you can't go backwards - the original scanner RGB has 
gone. However you do now have a scan in a known colour space (PCD) which can be 
mapped and tagged to any other colour space, sRGB, AdobeRGB etc. It's perfectly 
legitimate, nothing is broken - but you should regard VS internal working space 
as the device space here. So you don't want to go applying other profiles for 
the scanner, from other sources, at that stage, as the image is no longer in 
scanner RGB.

>(Tony
> ... correct me if I'm wrong ... I think this is what your
> 'step-by-step' Vuescan method implied.  This implimentation of "device
> RGB" makes me itchy, because while it is in Ed's evalutated "device
> RGB" space, it is NOT in the same RGB space as implied by a
> manufacturer supplied, or 3rd party calibration, device color space.

Quite. The whole point of VS is to avoid all that - either because VS does it 
better (=design aim) or because the OE scanner software doesn't use ICC at 
all.

> To impose (assign) one on top of the other makes me uncomfortable ...

It's an either/or proposition; you should never be applying scanner profiles to 
the Crop file. If you want VS to produce legit, tagged files, corrected for the 
scanner's deficiencies (and film characterisations too),
use the Crop file. If not, use the raw file, or other software, and DIY.

> I certainly am more comfortable with the scanned image inheriting the
> device space because nothing was done to it (... not implying the
> 'raw' scan' because we are still trying to use Vuescan's cropping
> tools ...) ...)

But VS doesn't implement CM 'properly' - if it did, Ed would have to bundle 
his scanner characterisations as ICC profiles and he declines to do that as 
everybody would pinch them and not buy VS. For the same reason, you'll find 
vanishingly-few PD profiles on the web, and people like Jon Cone making a 
living by selling them (for Epson piezos).

The downside is that this approach locks VS out of using any device profiles 
you might make yourself for your personal scanner/film combination, to 
produce the Crop file. However VS still gives you the wherewithawl to 
create and save a raw scan which you can then work with in PS, using 
device profiles or anything you like.




Regards 

Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner info & 
comparisons




 




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