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Alex: January 2009 Archives

Avid's DNxHD codec and Apple's ProRes are both riffs on the Cineform theme of high-quality digital intermediate codecs for editing.  Both offer more efficient compression than some competitors (especially at larger frame sizes), plus 4:2:2 chroma subsampling (which provides greater color fidelity than DV's 4:1:1 subsampling or MPEG's 4:2:0).  But the advantage of one of the other cool features -- support for 10-bit color depth -- has gone largely misunderstood or overlooked.  [Ed.: Some readers have asked me to emphasize that BOTH DNxHD and ProRes offer 10-bit color depth.  Apologies for any confusion.]

For starters, it's worth pointing out that each of the "extras" that ProRes confers may at first seem irrelevant: after all, broadcast NTSC still (for another month or so) uses YCbCr, and broadcast ATSC and DVB still use a variant of MPEG-2, with all the associated limitations.  Don't be fooled, though. 

Your post process almost inevitably involves changing the source image in some way or another, either through color correction, transitions, or any number of other processes -- and when you have all of the "extra" information in the ProRes picture, you're able to create an edited master that still has more information than you'd need for a "perfect" quality broadcast.  Similarly, you'd never edit in MPEG-2 directly (I hope) -- so using the higher-quality intermediate codec gives your compressor more "wiggle room" as the compressor tries to paint the highest-quality picture for the MPEG-2 transcoding step.

But enough of that ... more on bit depth specifically after the jump.
In Final Cut -- in a lot of different video applications, for that matter -- you may have wondered about Import/Export functions based on XML.  In fact, Apple made a big deal about Final Cut's XML Interchange Format when it first released, and for good reason.

As studios and production houses and newsrooms shift to a digital workflow, more and more pieces of the production process have to "talk about" the same footage.  At one broadcast network where we recently conducted training, the entire workflow -- from ingest to scriptwriting, roughing, package editing, promos, and output -- relied on a central media repository. 

Needless to say, that's a whole lot of pieces of software that need to talk to each other -- and making a separate copy of the source media for every step in the process is inefficient (imagine the extra disk space to hold 6 different copies of the same full HD footage for a 24/7 broadcast), not to mention confusing.
One of the most impressive new capabilities in Photoshop CS4 is direct integration between Vanishing Point and Photoshop's 3D Layers.  Why is this cool?  Because you can turn this still photograph (a higher-res copy, obviously):

photoshop-vanishing-point-3d-tease1.png...into a fully-navigable 3D scene, letting you do things like this movie (download MOV):
...without ever leaving Photoshop.
supercharging-compressor.pngYou can find more compression settings articles in our Supercharging Compressor series index.

Note: There's something about me and GOP articles ... just as I did on the first part of this article, I seem to have accidentally published a blank draft a few hours ago.  This is the finished version.  My apologies.

Compressor, like most reasonably advanced MPEG2 compression tools, offers you some control over the size and structure of your GOPs.  You'll recall from the first part of this article that 15-frame (1/2-second) GOPs are the norm for MPEG-2 video, and this is appropriate for a wide range of video types.  Similarly, Compressor defaults to using a lot of "B"-frames -- those are the frames that take the least information to represent, but that depend most heavily on neighboring frames of video.

Read on for situations when you might want to change this around ...

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This page is a archive of recent entries written by Alex in January 2009.

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