Re: sRGB is sRGB, right?
Re: sRGB is sRGB, right?
- Subject: Re: sRGB is sRGB, right?
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Fri, 05 Jan 2001 10:10:56 -0600
Dan Reid wrote:
>
When I plot the sRGB ICC profile created by Apple against the sRGB IEC61966
>
-2.1 from HP (manufactuer IEC?) I get slight descrepancies. What gives? Does
>
anyone know why there would be a difference between these two ICC/ICM
>
profiles?
I have discussed this topic before on this list. Technically, although the
two profiles are indeed different, both are correct. How can this be?
The sRGB colorimetric specification is with respect to D65. The ICC profile
specification is with respect to D50. Therefore, the sRGB reference
primaries must be adapted from D65 to D50 in order to comply with ICC
conventions. Unfortunately, the ICC specification does not have any
provision for dealing with the adaptation _algorithm_ used to accomplish
this conversion. If you examine the two sRGB profiles in question, you will
find that the profile "sRGB IEC61966-2.1" used the Bradford transform. The
Apple profile "sRGB Profile" used XYZ scaling. They produce different
results, but since the ICC specification does not indicate any preference
between the two, both must be considered correct.
If a finger must be pointed, it should be pointed to the ICC specification
because it neglects to deal with the adaptation _algorithm_. This oversight
is also the reason why you cannot guarantee Absolute Colorimetric results
from an ICC profile unless you know the adaptation algorithm that was used
by the software creating the profile.
--
Bruce J. Lindbloom, Pictographics Intl. Corp.