[Tig] Apple Color strange behavior

Jean-Francois Panisset panisset at gmail.com
Thu Aug 12 22:37:47 BST 2010


There has been a long-standing assumption on the Mac that all
RGB-encoded media has a native gamma of 1.8, whereas YUV/YCbCr media
has a native gamma of 2.2. This means that Mac libraries and apps (and
QuickTIme in particular) are forever applying "helpful" 1.8 -> 2.2 ->
1.8 gamma conversions, which works out to a gamma lift or drop of
around 1.222.

An example of this: take a QuickTIme created on a non-Mac platform
using an RGB-based codec, bring that into QuickTime Pro or Compressor
to transcode to a YCbCr-based codec (MPEG2 for instance), and you will
find a gamma lift of 1.222 has been applied.

The only Mac-based application that I know of that doesn't mess with
gamma at all is Shake (Nuke may also be in the clear, but I haven't
tested it yet). There's a helpful article in the Apple KDB that
explains the differences between the ways Shake and FCP deal with
gamma, I'm guessing that Color behaves more like FCP than Shake:

http://support.apple.com/kb/HT2912

There were rumors that under OS X 10.6, the default gamma for RGB
media would be changed from 1.8 to 2.2, but I have not been able to
verify if this is indeed the case.

JF Panisset
MPC
Santa Monica, CA

On Thu, Aug 12, 2010 at 9:51 AM, Rob Lingelbach <rob at colorist.org> wrote:

> Instead, I see a curve that appears to have a gamma of 1.22.  I have attached a figure of the RGB scopes below.  If I intercept the signal Apple is outputting to the grading monitor, it confirms this gamma 1.22 curve is indeed being transmitted to my grading monitor.
>



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