By Steve Owen, Quantel
So here we are in the middle of 2010 and there’s a new 3D movie being released every 10 days, the World Cup has just been broadcast in 3D and a number of broadcasters have already launched 3D TV channels. 3D has truly arrived, and is the subject on everyone in the industry’s lips at conferences, trade shows, TV conventions and movie festivals.
Incredible then that it was as recently as September 2007 when Quantel showed the world‟s first viable high-end Stereo3D post production toolset at IBC that year. Since then, Quantel has sold over 100 3D-equipped Pablo and iQ systems and these have been put to work on more Stereo3D movies and TV programs than any other system. This article draws on the experience of those many users to look at the new challenges that Stereo3D post production has set, and how these can be overcome in post production.
1. Use the right system
Stereo3D post production is all about getting the whole pipeline right and running at maximum efficiency. Stereo3D doubles the data load with its two hi-res streams, and demands that the two are handled in sync and in realtime – with random access to any frame or clip at any time. And the system has to do this reliably, 100% of the time, working with full quality images right there in front of the client. It takes considerable muscle to deliver that – time for a plug! – and that‟s why Quantel has sold over 100 3D equipped Pablos and iQs.
Stereo3D media is also twice as much hassle to move between suites – and when you do, you need to ensure that everything stays in exactly the right place. This is another reason why Quantel is so successful in Stereo3D – the systems have all the finishing tools onboard so you don‟t have to move the job around for fixes, titles, compositing, re-editing, playout of versions or anything else.
But even if you‟re equipped with the most powerful system available with great 3D workflow, it‟s still a new area with new challenges. So read on for some more tips that should help avoid the most common Stereo3D pitfalls and produce great work on time and in budget.
2. Shoot it right
Don‟t expect post production to get you out of trouble – the best Stereo3D is the best not just because of post production but also because of the way it‟s shot. However creative you are, you will not be able to turn badly shot material into a great result. Vince Pace, widely acknowledged as the world‟s leading expert on 3D, puts it this way: “Stereo3D depends on quality – no compromises. The secret of producing successful Stereo3D is in simply having a great team – that means experience, quality engineering, quality personnel and quality equipment such as the Quantel Sid and Pablo.”
Though the talent pool is growing fast, there is still a real shortage of people who know how to shoot great 3D. So if you‟re quoting on a 3D job, try and see the rushes first. If they‟re not great, ask yourself how much the pictures can tolerate being „pushed‟. If you need to use up all the headroom just getting the stereo right, then you won‟t have anything left to make the pictures look great. Great 3D on-screen means great shooting and great post! So be careful, and don‟t get stuck with a job where you are going to spend most of your time compensating for badly shot material; however hard you try it‟ll never look great.
3. The Depth Budget
The Depth Budget – yet another new Stereo3D term to learn! – describes the limits for negative parallax (in front of the screen plane) and positive parallax (behind the screen plane). Keeping within the depth budget will ensure that eye strain is kept to a minimum – it‟s all about what‟s comfortable to watch not just for a few minutes but for two to three hours at a time for a movie.
You might be surprised how comparatively small parallax changes are needed to produce Stereo3D. For example, Sky TV in the UK recently prescribed a Depth Budget of 2% positive parallax and 1% negative parallax (measured as a percentage of the width of the frame) for the vast majority of the material with short term impact effects not exceeding 4% and 2.5% respectively.
The Depth Budget is set when the material is shot – changing it in post requires the new picture information to be generated – something to be avoided if at all possible. Once again, good Stereo3D comes back to shooting it right in the first place.
4. The Depth Pass
All Stereo3D post production will include a Depth Pass, which involves manipulating the point of interest within the clip in Z-space to ensure that it is comfortable to watch while meeting the director‟s brief for where the point of interest of the scene should be – otherwise known as Depth Balancing or Depth Grading. This is the stage in the post production process where the need for jumps in accommodation between scenes are minimised, frequently using „Depth Dissolves‟. Realtime convergence control and full quality playback are vital for producing good, watchable stereo in the shortest possible time.
5. Target screen size
There are different issues to consider in Stereo3D post depending on whether the finished piece is intended for the big screen or front room TV viewing.
For TV viewing, “Edge Violations‟ (also known as “Breaking the Frame‟) need to be avoided or fixed. When objects that are positioned in front of the screen (ie in negative parallax) suddenly disappear when they pass out of the sides, top or bottom of the screen, this spoils the 3D illusion, so care has to be taken in post to avoid this wherever possible. This is much less of a problem when watching Stereo3D on a cinema screen as the screen is much larger, making edge effects less noticeable.
The Quantel toolset can create Floating Windows which can minimise the visibility of objects breaking the frame.
On the big screen, too much positive parallax causes the viewers‟ eyes to diverge – not something they ever normally do, and which will quickly become uncomfortable. This doesn‟t happen on a TV sized screen because it is not big enough! This problem is much harder to fix in post, and once again reinforces the value of shooting it right in the first place, with a sensible depth budget.
This is by no means a comprehensive guide to Stereo3D post production – that would require a book, but it is a distillation of the knowledge and experience gained by our many customers around the world who have worked on Stereo3D projects.
To conclude though, I come back to the main ingredients for great Stereo3D – the absolute necessity for well shot material to work with, a great pipeline to cope with all that data smoothly, onboard tools to make the inevitable fixes and an interactive workflow so that you can work with the client to make great Stereo3D.
Copyright Quantel 2010.