Explaining the Video Processing Tab

[ This article was first published in the April, 2006, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]

This technique was suggested by Bourne Ace, who wrote:

Larry I am having trouble understanding the Video Processing tab of Sequence Settings.

 

Could you help me out?

Larry replies: There are some little known settings inside Final Cut that can materially affect the final look of your sequences. When I mention these during my classes, I’ve discovered there is a lot of confusion about what these do, so here’s a more detailed explanation.

Your preference settings control what happens when you create a new sequence. However, once a sequence has been created, changing your preferences has no effect. To change the settings of an existing sequence, you need to open the sequence in the Timeline and make sure it’s active.

Then, go to Sequence > Settings.

Click on the Video Processing tab.

There are three sections to this dialog box. The top third determines render quality, the middle tells Final Cut how to handle white level processing, and the bottom third, which is new in FCP 5, affects rendering of motion effects. Let’s take a look at each one.

Video bit depth

The radio buttons at the top control the bit-depth that Final Cut uses to render your sequence.

Video bit depth determines how many shades of black and white, color, or alpha channel transparency each pixel can contain. 8-bit video allows 256 different shades of gray, or shades of a single color, such as red. 10-bit video allows 1024 shades of gray, or shades of a single color.

(Remember that the color of each pixel is determined by the mix of red, green and blue colors – so in a 10-bit environment, each pixel can have one shade to 1024 shades of red, one of 1024 shades of green and one shade of 1024 shades of blue.)

For black and white images, 8 bits is generally considered sufficient to represent the range of gray scale that is conveyed in a high-quality black and white photograph.

For color, however, 8-bit video is considered limited, especially when using gradients or compositing. In these instances, 10-bit video provides much better images.

Here’s how to choose.

• If you are shooting DV, HDV, BetaSP, or DVCPro-HD, select “Render in 8-bit YUV” because all these are 8-bit formats.
• If you are capturing using “Uncompressed 10-bit video,” select “Render in 10-bit…”
• If you are working EXCLUSIVELY with images created on your computer, for instance, animation, select “Always render in RGB.”
• If you want the highest quality for your compositing and effects, select “Render all YUV material in high-precision YUV.”

Update: Graeme Nattress notes:

Larry – have you ever seen setting this to “High Quality” to produce a quality improvement or difference? I’ve only seen bugs caused by > 8-bit render and much increased render times.

Update: Two notes: 1) All render files, regardless of quality, take the same amount of disk space, and, 2) video always creates YCrCb images and the computer always creates RGB images. When you are working with video always work in a YUV (YCrCb) color space. (YUV is the analog version of video, YCrCb is the digital form of video.)

Processing white levels

This setting determines how Final Cut handles white levels of imported graphics. This has NO effect on white levels inside video clips. (To control those you need to use the Broadcast Safe filter.)

Updated wording: The default for this setting changed in recent versions. In earlier versions of FCP, it was set to “Super-white.” In FCP 5, it is set to “white.” What’s the difference?

When you shoot DV, or create images on your computer, you are working in a pure digital grayscale space. However, analog video works in the more restrictive gray scale range of YUV.

Updated wording: In digital video, black is set to 0 on the waveform monitor. In NTSC analog, black is set to 7.5% (7.5 IRE to you video engineering types.) In Final Cut, always set your black level to 0. (In NTSC-Japan and PAL, analog black is set to 0.)

Update: Graeme Nattress writes:

It’s also good to differentiate between analogue voltages in IRE and FCP levels in % and not mix them. The % levels in FCP don’t always map to analogue voltages in the way you’d expect.

 

Most video formats shoot superwhite. If you have superwhite video in a white timeline, and do a dissolve even, you might see a luma shift effect as the rendered video gets clamped, whereas the rest does not. This setting doesn’t effect video unless it has a render.

Larry, again: In digital video, white is set to 109%, while in analog, white is set to 100%. The problem is when you broadcast whites that exceed 100%, the image will tear, edges will ripple, and there may even be a buzz in the audio.

Consequently, you need to make sure that your white levels don’t exceed 100% for anything you create that will be displayed on a TV set. These white levels are clamped in one of two ways: for graphics and text, and for video.

Video is clamped using the Broadcast Safe filter. Graphics and text are controlled from the Video processing tab. Here’s an example.

I’ve created a gradient that shades from white to black.

This is the waveform monitor with white levels set to “Superwhite.” See where the white level on the left exceeds 100%; shooting all the way to 109%? This far exceeds the technical standards for your TV set.

Here’s the waveform monitor with the white levels set to “White.” The image is the same. What’s different is that the gradient has been “clamped,” or adjusted, so that the maximum white level does not exceed 100%; making it safe to broadcast.

Updated wording: The rule is clear. If you are outputting to DV or the computer, and never expect to view your work on a TV set, you can set this pop-up menu to “Superwhite.” However, if you want to be safe, leave this set to “White.”

Motion filtering

New in FCP 5 is the bottom menu — motion filtering. This controls the quality of your renders for motion effects, including scaling and rotation.

In FCP HD, Apple chose to have everything render in “Fastest” mode. This provided the greatest speed, but there were problems with objects that changed in size or rotation. They wouldn’t look as good as they could.

So, with FCP 5, Apple provided two more choices: “Better” and “Best.”

In general, if you are creating motion effects, that is, you are changing settings in the Motion tab of the Viewer, you will get improved quality by changing these settings.

Here’s the rule: you can set your render settings to “Fastest” while you are editing your project. However, when you get ready for final output, change your setting to Best and re-render.

Update: Tom Wolsky adds:

Tests have indicated there is no real difference between Normal and Best, and the render hit in time is pretty big.

Larry, again: Changing this setting will ALWAYS delete all your existing render files for the currently active sequence.

However, there’s a bug in the current version of Final Cut (5.0.4) that effects this decision. If you add a keyframe for rotation, even if you only add one, your motion filter settings automatically reset back to Fastest.

If you are not changing motion tab settings, you can ignore this. If you are, experiment with these settings to see whether the improved quality is worth the extra rendering time. And, remember, rotation keyframes reduce the quality back to the same level as can be achieved in FCP HD.

 

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