Premiere Pro has a comprehensive suite of Video Effects in the box – blurs, warps, colour correction, and very powerful and precise chroma keying. Here we’ll look at the results achieved with the Ultra Key effect by hardware-accelerating the Mercury playback engine that drives Premiere’s real-time effects.
We’ll use a workstation accelerated with NVIDIA’s Maximus technology, which uses the company’s CUDA platform to combine a Quadro workstation-class graphics card with a Tesla companion card, delivering extreme performance. CUDA can tap a Quadro graphics card alone, but by including the Tesla card as well, we can achieve real-time full-resolution playback of multiple streams of mixed-format video, with a live chroma key.
The Ultra Key plugin allows us full control over the isolation of our subject from its background, while retaining the fine-edge detail around hair and clothes, all in real time. There are also controls for removing reflected colour artefacts via Spill Suppression and Colour Correction.
Here is a very complex nested sequence with many layers of video of different formats, and a variety of colour corrections, motion effects and mattes applied. In this instance, the system has been set to ‘Mercury Playback Engine Software Only’.
The timeline has a red bar at the top, and we have had to drop Playback Resolution to ¼. The system activity monitor indicates that the CPU cores are under high load; frames are being dropped.
Now we’ll use exactly the same timeline with the project set to ‘Mercury Playback Engine GPU Acceleration’. The timeline now has a yellow bar, and plays in real time at full playback resolution.
The CPU load has dropped substantially, thanks to the NVIDIA GPUs on the Quadro and Tesla boards taking up the video effects processing load.
Open the Effects Panel. It’s easy to find the effect you’re looking for using the Search box in the top left.
You can click on the ‘Accelerated Effects’ icon at the top left, shown in yellow, to restrict the list to display the many effects that are accelerated using NVIDIA’s CUDA technology. If you don’t havea CUDA card in your system, these icons will be greyed out.
Having created a sequence containing a clip shot against a monochromatic background, select the ‘Ultra Key’ effect from the Effects Panel, and drag it across to the shot in question. With that clip highlighted in the sequence, open the Effects Controls Panel.
Check that the panel indicates the name of the shot you are working on. Clicking on the triangle next to Ultra Key effect reveals the control parameters groups – Output (what you see in the Viewer), Setting (level of processing intensity), and Matte Generation, Matte Cleanup, Spill Suppression and Color Correction.
Click the Eyedropper next to the Key Color swatch. You can then click in the background portion of your image itself to sample the correct hue and saturation of the subjects’ background.
Click on the ‘Output’ dropdown to see the three display modes available for the Ultra Key effect – Composite, Alpha Channel and Color Channel. Select Alpha Channel to see a representation of the alpha matte being created by the effect.
Click on the ‘Setting’ dropdown and select ‘Aggressive’. This increases the effect processing intensity to the maximum, maintaining as much edge detail as possible – so it’s a good thing we’ve got our Quadro and Tesla boards to accelerate the process and maintain real-time performance.
You will notice in this case that the lighting on the greenscreen had poor uniformity, so there are still areas of the matte that need cleaning up.
Click on the ‘Matte Generation’ disclosure triangle to play with Transparency, Highlight, Shadow, Tolerance and Pedestal parameters until you achieve a matte that is as clean of background image as possible.
The values shown here (40, 10, 75, 90 and 50 respectively) give an indication of the ranges to work within.
Here we see the result after some time spent tweaking the parameters. We have achieved a very smooth matte excluding almost all of the extraneous background of the image. You can flick between the ‘Composite’ and ‘Alpha Channel’ outputs to check the integrity of the foreground subject.
Here we see the clip during playback, with the Ultra Key effect active. The yellow line above the timeline indicates that the system load is very low, that the Quadro and Tesla boards are taking the strain of the keying process.
There’s still a problem with our shot though. Besides being poorly lit, it’s also poorly framed, and the greenscreen background does not fill the frame. This leaves a remnant of the backdrop in the image. We need to crop this out.
Select one of the ‘Garbage Matte’ effects from the Effects Panel. Use the parameters for the Garbage Matte shown. Changing these values will move the position of the matte’s corner points within the image.
Modifying the ‘Garbage Matte’ effect can also be achieved by dragging the visible corner points around. The screen grab right shows the uncropped image, while the shot above shows the image with the Garbage Matte crop in place.
Here we have switched the Ultra Key output back to ‘Composite’, and superimposed this shot on top of another panning shot on the Video 2 track. The Video 1 shot with the Ultra Key effect was shot at 1080p on Panasonic DVCPro HD 100 (P2). The background image on Video 2 is 1080p also but at a very low bit rate, shot on a Samsung Galaxy S2 camera.
As you can see the system is capable of mixing the two formats in real time despite the DVCPro footage being Thin Raster (its real resolution is 1280 x 1080), and the S2 footage being full-frame HD (1920 x 1080), and with a different frame rate.
The timeline’s yellow bar shows that CPU load remains low because the Quadro and Tesla boards are providing the Ultra Key, the image scaling, and the blending between the two video channels. Performance is real time with no dropped frames.
Tip: Seamless set-up
It only takes a single step to configure Premiere Pro to take advantage of the power of Quadro and Tesla cards. Open Premiere Pro and select Project > Project Settings and then the General tab. Ensure you select ‘Mercury Playback Engine GPU Acceleration’.
Tap the power of Maximus
With a Maximus workstation, you can edit and encode video faster, better and more accurately than ever before. Offering a combination of GPU-based acceleration from both NVIDIA’s Quadro graphics cards and Tesla companion boards, a Maximus workstation delivers real-time performance that’s just not possible in software alone.
Edit in real time with more layers, and combine complex effects without having to settle for low-resolution previews – with Maximus you can see your work exactly as it will appear when output. And when it’s time to produce your completed project, you’ll see almost six times the performance of a similarly priced rendering/encoding station. Maximus enables you to spend more time being creative, and less watching crawling progress bars or guessing how an effect will be rendered. All this allows you to produce better work and hit tight deadlines with room to breathe.
To learn more about how Maximus can help take your workstation to the next level, visit www.nvidia.co.uk/maximus
Adobe Premiere Pro CS5.5 performance editing
Premiere Pro CS5.5 is part of the Creative Suite 5.5 Production Premium and Master Collection, as well as being available separately. The video editing application is underpinned by the Mercury playback engine.
This is the name given to describe the performance gains achieved now that the application is natively 64-bit and multithreaded. In many cases you can achieve realtime playback with native camera files, often even while mixing a range of formats and effects in a single timeline.
Further improvements to the workflow result when using a qualified NVIDIA CUDA-based graphics card, which allows many video effects to run natively on the GPU, freeing up resources and increasing overall system power.
For more details visit www.adobe.com/products/premiere