21 Jun
2015
21 Jun
'15
3:42 p.m.
Hi Jim,
While teaching a group of people how to use
DCP-o-matic last weekend
(DCP-o-matic is now on the syllabus at London Film School!), I came
across the change in v1.79.0 that default colour space conversion is now
Rec709.
For the majority of the people who'd brought their film to test on, we
found that sRGB was the best setting for them. We were comparing their
source files (mostly Quicktime) to the resulting DCP viewed in Doremi
Cineplayer (evaluation version) and found that Rec709 was changing the
colour balance of the image (most notably, making it darker).
What was the rationale for changing the default to Rec709?
Rec. 709 is thought to be the best guess for HD (i.e. roughly 2K pixels
across) material; it is the default output from Final Cut Pro 7, for example.
And is there any way to examine a Quicktime file to
find out what colour
space it's in? With shorts filmmakers, they often don't know themselves!
There is, unfortunately, no easy way to do this. There are some
QuickTime headers that you can read with tools such as QT Edit
(http://www.digitalrebellion.com/promedia/) but I haven't personally
tried that.
Presumably the default output from Final Cut Pro,
Premiere Pro etc
remains sRGB rather than Rec709?
This would seem unlikely. Almost all "video" formats represent colour
as YUV, not RGB, so use of the sRGB colour conversion settings doesn't
make much sense.
It's strange that sRGB is closer to Cineplayer for you than Rec. 709.
If you use sRGB with DCP-o-matic you are going to get a gamma
correction which results in a lighter image than that for Rec. 709, and
it is odd that Cineplayer "agrees" with that lighter gamma.
Have you ever compared the output of Cineplayer on your system to a
projected image? Is it accurate?
Best regards,
Carl