Re: Responce to Chris
Re: Responce to Chris
- Subject: Re: Responce to Chris
- From: Phil Green <email@hidden>
- Date: Fri, 25 May 2001 17:43:40 +0100
- Organization: LCP
Eds Smith wrote:
>
Chris writes about the fact that there are 16 million colors in the sRGB
>
color space. That is not completely factual. The computers Hexadecimal
>
numbering system necessitates that ANY 8 bit / channel RGB color space is
>
divided up into 3 channels of 256 levels, which equals a theoretical
>
16,777,216 colors.
I think you are confusing the encoding space with the realizable gamut.
Sure there are 3x8bits of encoding space in any 3-channel 8-bit
encoding. The difference is that all the possible encodings in an RGB or
CMY(K) space correspond to physically realizable colours, while the
majority of encodings in an 8-bit CIELAB encoding are not realizable -
don't even correspond to visible colours. The fact that some colours in
the encoding are not discriminable from each other is a different issue.
>
> Also, ICC LAB is not infinite, and many RGB working spaces include
>
> colors outside of ICC LAB.
>
Are those colors reproducible on any device besides a theoretical model?
Not reflective colours but CRTs. In the case of AdobeRGB this applies to
all intensities of green primary with L* above about 50. Although
AdobeRGB green does not correspond to the phosphors of real CRTs, it's
possible to make them. EBU green phosphor at max intensity is also
likely to be outside the 8-bit encoding range.
The +/-127 limit is not just a feature of the ICC spec but of TIFF and
other common encodings.
--
Phil Green
Colour Imaging Group
School of Printing and Publishing
LCP
Elephant and Castle, London SE1 6SB
Tel: +44 020 7514 6759 Fax: +44 020 7514 6772
http://twinpentium.lcp.linst.ac.uk/digitalcolor/cig