Re: sRGB vs. sRGB IEC61966-2.1
Re: sRGB vs. sRGB IEC61966-2.1
- Subject: Re: sRGB vs. sRGB IEC61966-2.1
- From: Graeme Gill <email@hidden>
- Date: Fri, 13 Sep 2002 14:13:47 +1000
John Gnaegy wrote:
>
> different. As it was explained to me by John Gnaegy - the Apple
>
> version uses the Bradford transform and the industry standard version the XYZ
>
> transform.
If by "Industry standard", you mean the one at www.srgb.com, then
it too uses the Bradford transform, see <
http://www.srgb.com/c55.pdf>
>
> I'm also advised that Kodak have another variation.
This would seem to work against the idea of a standard.
>
The alternative to Bradford is the Von Kries transformation. All the
>
profiles Apple now ships use the Bradford transform. XYZ is a kind of
>
intermediate space called a PCS (profile connection space), and its
>
alternative is Lab. Bradford vs. Von Kries, XYZ vs. Lab.
Not a reasonable comparison. The transform between XYZ and Lab is
(for any practical purpose) exact and reversible. Colors
transformed through one white point transform, and then reversed
through another, will generally not result in the same color values.
(Note that technically the Bradford transform is a Von Kries transform.
A Von Kries transform is a linear white point adaptation performed in a
sharpened cone space. The Bradford transform refers to a Von Kries
transform in a particular sharpened cone space).
>
The only difference between sRGB IEC61966-2.1 and the sRGB Profile
>
Apple ships is at the low end of the gamma curve. The standard
>
specifies a linear response at the very darkest end of the range, then
>
a 2.2 gamma curve for everything else.
This should read "2.4 gamma curve". See <
http://www.srgb.com/srgbgammacalculation.pdf>
>
Apple's sRGB Profile is a 2.2 gamma curve for its entirety, which
>
can be described by a smaller profile.
Is it really sRGB though, if it differs from the standard (albeit, to
a minor degree) ?
Is there a reason different vendors are cooking up their own sRGB
profiles, rather than using the ones from sRGB.com ?
Graeme Gill.
_______________________________________________
colorsync-users mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/colorsync-users
Do not post admin requests to the list. They will be ignored.