Re: Apple RGB
Re: Apple RGB
- Subject: Re: Apple RGB
- From: Richard Wagner <email@hidden>
- Date: Tue, 29 Apr 2003 14:08:50 -0700
Roger Breton <email@hidden> wrote:
>
I think the name "AppleRGB" was coined by Adobe not Apple. Just as
>
Adobe
>
coined "Euroscale", not some european printing authority. But that's
>
OK.
I'm not sure if "coined" = "created" but Adobe says Apple RGB was
created by Apple...
<<<
http://www.adobe.com/support/techguides/color/cms_glossary/A.html
Apple RGB
The RGB working space created by Apple Computer, Inc. that reflects the
characteristics of the Apple Standard 13-inch monitor, and is used by a
variety of desktop publishing applications. >>
With regard to the 1.8 Gamma (which is no longer the gamma of choice
on Macs or PCs... neither of which generally use dithering or indexed
color with LUTs anymore):
<<
http://www.color.org/sRGB.html
LUT gamma
Two special circumstances will lead computer systems to systematically
deviate from the 2.2 CRT gamma and the 1.0 LUT gamma that we propose -
color dithering for 16 color systems and system imposed gamma
correction via look-up-tables (LUT).
The first of course was very common until a few years ago. Until about
1993 most Windows PCs were well described by a display gamma of 1.8
because despite having 2.2 CRT gamma systems, the colors were dithered
into the 4 bit frame buffers, resulting in a flattening of the system
transfer function. This happens because screen dithering mixes colors
linearly in the eye, making it less dependent on the CRT non-linearity.
Since currently most Windows PC support 16 or 24 bit color modes, 2.2
CRT gamma is now the average.
The second systematic deviation happens when the graphics system in the
computer hardware or software imposes its own gamma correction. This is
done for a variety of reasons, but is usually an attempt to compromise
between image display and graphics/image processing performance (most
computer graphic rendering assumes linear radiation space, e.g.
transparency operations, and so does image processing, e.g. scaling and
filtering). The gamma correcting of image data can be described by
applying an exponent to the image data. For the Macintosh the display
gamma is around 1.571 using a LUT gamma of 1.4 (2.2/1.4 = 1.571) and
for SGI workstations the display gamma is around 1.294 using a LUT
gamma of 1.7 (2.2/1.7 = 1.294).
There has been significant confusion derived from assuming the CRT
gamma value is identical to the exponent in equation 0.4. This has led
to many claims of CRT gamma values of 2.5 for video, 1.8 for the Apple
Macintosh and 1.4 for SGI monitors. Unfortunately, it has been our
experience that this misconception is not well founded in the actual
physics of the displays and solid measurements. >>
--Rich
<><><><><><><><><><><><><>
Richard Wagner
email@hidden
www.WildNaturePhotos.com
Member ASMP | NANPA
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