RE: filmscanners: Vuescan: "device RGB"

["shAf" <michael@shaffer.net>]

Richard writes ...

> There is a lot that doesn't add up - - regarding PCD
> "space", and VS using PhotoCD "space".
>
> 1. You will note that you cannot do a profile
> conversion (profile to profile) in Photoshop ...
>
> 2. PhotoCD format - - and their ICC profiles ARE
> proprietary, ...
>
> 3. If you examine each PhotoCD ICC profile, you will see a
> number of CLUT listing, and the sources are labeled
> "secret". That word. ...
>
> 4. You can open a PhotoCD - ... you cannot
> embed (or format) Kodak's space.

        Probably the reason I found so little info regarding the color
capacity of PhotoCD space when I visited Kodak this morning ... plent
of info, yes ... but nothing to relate it in terms we use in the
normal context of profiles.  Still, the transforms were easily
downloaded, and I didn't have to sign or accept anything.  Presumably
Ed knows what he's doing, has permission, and simply anything remotely
associated with embedding PCD RGB.

> 5. If VS uses PhotoCD, what is he (Ed) using for tables,
> if the CLUTS are proprietary?
> ...  In an (off-list) correspondence with me Ed
> championed sRGB ...

        I cannot imagine he is using sRGB as an intermediate color space ...
it would then make any sense to offer other color spaces as sRGB is
the smallest.  Someone will simply have to ask him.

> 6. The scanner has its own RGB color response, ...
>  Most modernscanners have RGB responses far in excess
> of the media they scan, ...
> ... In fact, the Nikon LS1000 has a gamut,or
> color response that well exceeds Ekta Space; ...

        Interesting!  PS6 allows for rough comparisons of the LUT-type
profiles included with the LS-2000.  "Nikon_wide" was only a bit
bigger than Ektaspace (if you can believe the trismusthus intercept
PS6 calculates being a fair comparison).  According to Bruce Fraser,
PCD RGB isn't much larger either, but definitely large enough to not
clip scanner space (debatably), and to offer lossless conversions to
most working spaces (the exception being ProPhoto, which according to
Bruce is quite a bit larger than PCD RGB)

> 7. ...
>
> 8. All Kodak PhotoCD profiles exhibit very unusual gamut
> profiles, in either L.a.b., Yxy, or XYZ space.
> The are all complex. ...
> I don't know why Ed would even consider these spaces - -
> unless for PR reasons.

        When you say "all the PCD profiles", wouldn't Ed simply be using the
most appropriate one.  And, wouldn't this one offer a standard model
for mathematically converting to & from???

> 9. If VS is using some sort of "space" which alters
> the RGB values, and then doesn't "tag" the resulting
> image - you never know  how much distortion
> has been introduced from "real" values.

        After looking into it only a little bit, I came away believing PCD
RGB is sufficiently large and well defined to be used as an
intermediate space.  Vuescan does tag the images it exports in a
variety of working spaces (including ProPhoto and Ektaspace), the only
offering it doesn't tag is "device RGB" ... and it should be easy to
see if it is anything remotely resembling sRGB.  I'm quite curious ...
I would ask VS for an sRGB image, and Ektaspace image, and the "device
RGB" image.  Depending on which resembled which, as you assigned the
working space to dRGB with PS6, it should be obvious.

shAf  :o)