Re: HDTV icc profile
Re: HDTV icc profile
- Subject: Re: HDTV icc profile
- From: Dan Reid <email@hidden>
- Date: Tue, 25 Mar 2003 17:07:41 -0700
on 3/25/03 1:40 AM, Shadi el-Hajj at email@hidden wrote:
>
hi,
>
thanks all for your help, let me try to get this straight :
>
>
> A.K.A, sRGB IEC61966-2.1, available in Photoshop v6 and higher.
>
> sRGB uses the HDTV chromaticies of ITU-R 709-2. HDTV monitors have a gamma
>
> response of 2.2 and white point of 6500K.
>
>
>
but does this mean sRGB and ITU-R bt.709 are strictly identical ? they
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have the same whitepoint and chromaticies that's for granted. however
>
ITU-R bt.709 specifies:
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>
Overall opto-electronic transfer characteristics at source(1)
>
V = 1.099 L<superscript>0.45 ? 0.099 for 1 ? L ? 0.018
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V = 4.500 L for 0.018 > L ? 0
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where:
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L : luminance of the image 0 ? L ? 1
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V : corresponding electrical signal
>
You got me. That's more math than I care to work with.
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and then:
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Conceptual non-linear pre-correction of primary signals: gamma = 0.45
I don't know about this either.
>
>
what i don't understand is how that relates to gamma 2.2 ? (excuse my
>
ignorance if i am saying a heresy here).
Both the NTSC (1953) and SMPTE-C ICC profiles use a gamma of 2.2 in their
profiles so I think the HDTV would follow that lead.
>
moreover, the quatization levels for 8 bit state that black level should
>
be 16 and nominal peak 235, doesn't this mean that the original 0-255
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signal; should be remapped to fit the 16-235 range ?
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thanks again.
>
>
cheers,
>
shadi
>
The ICC profile correctly compresses signals to fit with the 16 - 235 range
of broadcast standards even though the file will still relate to 0-255
because it's an 8bit file. You don't need to manually compress the signal to
16-235 as the profile handles that for you. Give it a try. I have had pretty
good results but maybe I missed something.
Good questions.
--
Dan B. Reid
RENAISSANCE PHOTOGRAPHIC IMAGING
http://www.rpimaging.com | email@hidden
Toll Free: (866) RGB-CMYK
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