Re: Designers, Color Management, and Xrite , some thoughts and comments.
Re: Designers, Color Management, and Xrite , some thoughts and comments.
- Subject: Re: Designers, Color Management, and Xrite , some thoughts and comments.
- From: "email@hidden" <email@hidden>
- Date: Sat, 19 Apr 2008 18:01:33 -0400
Hi Uli,
There are very good technical reasons for gamma 2.2 as a native
response. These reasons long pre-date the Mac and PC battle. I am NOT
trying to change your mind on this issue, because frankly, from the
standpoint of the Mac, you are right. Once they moved all their media
players to that mode, the die was cast.
Rather than call the PC a gamma 2.2 platform and a Mac a gamma 1.8
platform, I would call a PC a gamma-do-nothing platform, and Mac a gamma
1.8 transfrom platform. In a very grotesque fashion, Apple is actually
pseudo color managing all the media. Lets take a closer look at this:
Gamma 2.2 comes from two primary standards Rec 709 which had a 2.2 gamma
assumption and now has a "gamma" like transfer function proposed for
output from video cameras. sRGB borrowed the Rec 709 primaries and
introduced a slightly different transfer function that basically follows
a gamma 2.2 intent. There is a native gamma 2.2-like assumption for
both still and motion video (but they differ a bit in the details) .
Displays are generally set to around gamma 2.2 native, so the
"gamma-do-nothing" strategy works pretty well.
The two predominant specifications for digital video are divided by High
Definition (Rec. 709) and Standard Definition( Rec .601? I am not sure
that I have that spec number correct and I am not in the US today).
These two specifications have slightly different primary assumptions and
slightly different transfer functions, but both transfer functions are
close to gamma 2.2 in application. All moving media use a basic gamma
2.2 assumption. Apple's committement to gamma 1.8 means that they must
basically change the transfer function in all applications that import
video content to gamma 1.8. This would also imply that all
applications, must convert from Mac Gamma to some assumed gamma or
transfer function based upon the media when exporting. So we have here
a platform that universally must "touch" every piece of content that
passes through it.
Now here's the problem: if you are going to "touch" the content, then
you must touch it with great care. What we have learned from HD digital
video, standard def digital , and sRGB is that simple gamma manipulation
used multiple times will degrade the image, particularly in 24 bit rgb.
Each of these media, deal with the problem in a different way, by
introducing a linear portion in the dark areas that converts
unambigously via look up table and is also invertable via look up
table, so there is no digital roundoff or clipping with each subsequent
operation. More power to Apple if they are doing this, but given the
diffuseness in their technology across so many different groups, I
really do doubt that this is being handled universally correctly. A
transform to simple gamma 1.8 will, by definition, quantize the shadow
detail. This means that multiple editing sessions of the same media
will degrade the image.
So for the simple user, it might make sense, but for the pro, it IS a
real issue. Now I hope you better understand the technical reluctance
to move the product to gamma 1.8 . For a platform that emphasizes media,
holding on to Gamma 1.8 is an odd choice.
Regards,
Tom Lianza.
Uli Zappe wrote:
Am 19.04.2008 um 19:13 schrieb Uli Zappe:
If everything worked reproducibly (between different applications
etc.), then a few options wouldn't heard anybody.
uhm, that's "Hurt", not "heard" ... - sorry!
Bye
Uli
________________________________________________________
Uli Zappe, Solmsstraße 5, D-65189 Wiesbaden, Germany
http://www.ritual.org
Fon: +49-700-ULIZAPPE
Fax: +49-700-ZAPPEFAX
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