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     áòèé÷ :: Filmscanners
Filmscanners mailing list archive (filmscanners@halftone.co.uk)

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Re: filmscanners: creating correction curves from scanned calibration chart?




I've come of retirement for this one :-)

>From: Todd Flashner <tflash@earthlink.net>

>However, for a neutral gray
>they (RGB) SHOULD all be the same number.

no, total rubbish. the profile defines the relationship between the value 
and the actual colour output. Profiles do NOT attempt to balance the RGB or 
CMYK or CMYKOG or whatever values, they are simply the actual transfer 
functions between RGB (say) and XYZ (for example). They could be 157,23,45 
for mid grey - it doesn't matter.

>Forget what Ned said about RGB
>being device dependant (sorry Ned), that was pre Photoshop 4, when your
>monitor profile was used as your system profile (before my time so don't
>ask). The idea of abstract color spaces, like Adobe RGB, or sRGB, is
>precisely that they ARE device independent.

Adobe RGB and sRGB are simply attempts to define a device-independant RGB - 
which is totally pointless when you could use XYZ or even at a push LAB, but 
they are there so most other programs like image viewers and web browsers 
can simply display the images raw without any colour transformations and 
still look reasonable. Those two profiles are hopelessly compromised and 
should be avoided if at all possible. If your scanner outputs in a true 
device-independant manner, such as LAB, choose that.

Ned



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