Re: filmscanners: which space?

[TREVITHO@aol.com]

Dear Karl

As CMYK is a much reduced colour space compared to RGB I would have thought 
that made it exactly the case. The true test would be to make multiple 
conversions from RGB to CMYK and back and see if quality suffered, which of 
course it does.

The real test would be to make the conversion several times in different 
programmes. 

R=25%, G=15%, B=10% converts to:-

QUARK           C25 M50 Y65     K64
PAGEMAKER   C56 M74 Y83 K65
FREEHAND        C75 M85 Y90
PHOTOSHOP   C41 M62 Y69 K70

It all depends on your standards. For LVT output you can't even make one CMYK 
to RGB conversion without noticing adverse quality; for web use you can 
probably get away with several. 




In a message dated 26/5/01 8:29:01 am, karlsch@earthlink.net writes:

<< That's not exactly the case.  What is the case is that a particular Hue,

Intensity value - what our eyes perceive as a unique 'color value' can be

rendered with multiple combinations of RGB.  The same is not true for CYMK


So when you map from RGB into ANY color space, you essentially lose some

information.  Namely you lose the mapping back to the original value

settings.  That doesn't mean you can't get back to an RGB triplet that will

look the same, but it does mean that say if you had set the RGB triplet

value to Rx,Gy,Bz then mapped to CYMK and you went back, Rx',Gy',Bz' might

not have

x=x',y=y',z=z'.


This matters because you then can't just 'undo' any filtering you did prior

to the mapping.  Other color spaces have unique tuplet values.  This has to

do with the fact that in CYMK, intensity is mapped into the gray-scale K,

whereas in RGB, intensity is a function of the particulare RGB values. >>



Bob Croxford
Cornwall
England

www.atmosphere.co.uk