Re: The color of QuickTime 5
Re: The color of QuickTime 5
- Subject: Re: The color of QuickTime 5
- From: Eric Blanpied <email@hidden>
- Date: Thu, 04 Oct 2001 17:10:54 -0700
I know I'm chiming in a bit late, but someone just alerted me to this
conversation a few days ago. I work in the QT Engineering group at apple,
and while I don't do anything connected to ColorSync, I hope to help a bit.
You'll also need to deal with a less-than-thorough knowledge of color
management. I know PhotoShop well, and have been using it for multimedia
work for something like ten years, so I have been exposed to it all. Correct
me if I blow it.
On to the topic:
It sounds as though some users expect some kind of on-the-fly color control
of QuickTime movies, similar to the control provided for still images in
various apps. This is a tall order at present.
First off, the business of color matching a still is a discreet process:
apply the profile and display the image. It doesn't matter if it takes time
because it's a one-time event. Sure, you may need to do other
transformations as operations are conducted, but again, they are one-time
events.
Displaying QT movies is a continual process of decompressing frames and
displaying them. This process must occur on schedule, for obvious reasons.
For many codecs (compressor/decompressors) it can be rather
processor-intensive.
So an on-the-fly color matching system would have to fit into that. It would
need to intercept the image data somewhere in this process, apply the
profile and hand the new image off to be displayed. There are numerous
places that could occur, but they're all going to take time.
This is what the ColorSync QT Effect does, and as someone pointed out, a
fast processor is required for clean playback. I haven't tried it in some
time, but the final playback speed will depend on lots of factors, such as
frame size, frame rate, codec choice, other processor tasks (audio
decompression), etc.
Why not do it in QT Player?
QT Player does as little as possible to display a movie. It just drives QT
in as generic a manner as possible. By having QT do all the work other apps
get access to the same functionality (as long as they're written to use QT
as recommended).
How else could you do it?
Anyplace in the chain from file to screen. I could imagine a system which
takes color profiles into account while decompressing, producing a color
managed image right from the start, but different codecs work in very
different ways, so this would probably have to be handled in each codec.
This would be tons of work, and more prone to problems.
The most modular approach seems to be something which does it's business
after the codec has handed QT an image, and before the image has made it to
the screen. Which is right where QT Effects fit in, so it seems like that's
the right place.
Depending on your project (and audience), you may be able to optimize the
movie enough so that the ColorSync Effect doesn't cripple playback. I
suspect it would have to be a rather low-framerate movie.
If you're looking for color-management in the editing process, then playback
speed might not matter.
The other problem with the QT Effect approach is that the app makers need to
support it for you. You can apply the Effect using our free tool
(MakeEffectMovie, www.apple.com->qt->developer->tools), but if you want
After Effects, Premier, Final Cut, etc. to pass color-managed movies around
between them then those apps need to add the effect tracks, and use them
when they encounter them. Ask for it.
Has that helped at all, or does it just muddy the waters?
--
Eric Blanpied
QuickTime Engineering
Apple Computer, Inc.