Re: absolute luminosity
Re: absolute luminosity
- Subject: Re: absolute luminosity
- From: Roger Breton <email@hidden>
- Date: Sun, 13 Nov 2005 10:10:24 -0500
Eugene,
> I am using the word tone to distinguish out of gamut values from out of gamut
> tints and saturations.
OK.
> I am making the distinction because it appears as
> though the gamut warning makes it also. L* 0 would have to be out of range of
> every output profile yet gamut warning does not show this.
You are 100% right. To test this, I opened up a pure grayscale Lab image
made up of only a=b=0 "tones" going from 0 to 100, and, as you said, Out of
gamut Warning does not show any out of gamut colors here? So, I would have
to say that this feature is broken or severely crippled. Thank's for
bringing up!
> When comparing the
> colour spaces in Colorthink I can see clearly where the lower edge of the
> space is. These shades of colour protrude through the lower perimeter of the
> ouput space and are considered ³out of gamut².
Right.
> I am not sure why gamut warning clicks in when it does, for example using the
> same settings that you describe * swop v2 from Adobe RGB with relative ² it
> shows me that L*13 32, -13 is out of gamut, but everything down from L*13
> (L*12, 32, -13 to L*0, 32, -13) is shown to be in gamut.
Or at least "is not shown to be out of gamut" ;-)
> I can use soft proofing to see the maximum shadow of the output space, since
> it occurs visually on the screen. Without BPC all tonal distinctions south of
> the maximum shadow disappear, The info pallet shows me the data where the
> first visual distinction occurs, but gamut warning does not.
That's crazy.
> I had assumed, because of the difference in gamut warning while soft proofing
> with absolute and relative, that absolute was showing me the out of range
> tones, but the logic is inconsistent
To say the least!
> and appears to function differently with
> RGB output and CMYK output profiles. The only way to truly know for sure would
> be by applying the gamut warning to grey scale files but this is not possible.
OK.
> Ok I have rescanned the 4x5 transparency on the Eversmart to produce the exact
> same highlight value (in lab) as the Epson scan. Both scans now indicate L*88
> with relative configured in colour settings . The RGB data is of course
> different because the files are still in their input profiles. If I change the
> colour settings to absolute the Epson file remains the same and the Eversmart
> file drops to L*68.
>
> «énigme!» comme dirait Michel Rivard
>
> Thanks for your help.
>
> Eugene Appert.
Could you send a small sample file offlist with the reference data? I'd like
to replicate your findings here.
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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