Final Cut Pro HD | H•O•T Hands-On Training [Electronic resources] نسخه متنی

1.

If Final Cut is not running, start it and open Chapter 11 Lesson. Double-click Seq Key Chroma to load it into the Timeline. Double-click Track Jump to load it into the Viewer. Click the Filters tab to make it active. Position your playhead on the marker.

You are going to create a surreal sky as a background for a snowboarder. To do this, you will replace the blue sky with a computer-generated background.

A couple of notes before you start. First, the snowboarder was not shot with chroma key in mind. Because of this, you won't get a perfect key.Don't worry about perfection; concentrate on learning the process.

Second, I knew at the outset that I was not going to get a perfect key, so I selected a background that would hide any blue edges caused by a poor key. Inserting a background with a similar color to your chroma key color is a useful technique when you know that "pulling a clean key" (creating the effect) is going to be difficult.

Third, this effect can be improved by first color-correcting the snowboard shot, then pulling the key. You already know how to color-correct a clip, so you can experiment with it for extra credit at the end of this exercise. I suggest you put the color correction filter in first, then add the chroma key filters.

2.

The process of chroma keying involves three different filters, and they need to be applied in a specific order. So, select Track Jump, then choose Effects > Video Filters > Key > Color Smoothing 4:1:1. This filter tries to compensate for the loss of color created by compressing video to DV. This filter is either on or off. Leave it on.

Next, choose Effects > Video Filters > Key > Chroma Keyer. This is the filter that does the heavy lifting.

Finally, choose Effects > Video Filters > Key > Spill Suppressor (Blue). This filter compensates for blue halos around your subjects, after you create the key. I've found this filter to be only somewhat useful. For now, turn it off.

3.

Click the Visual button on the Chroma Keyer filter. This switches the filter from a numeric display to a visual interface.

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The chroma key filter is divided into three sections: color selection, edge enhancement, and controls. You'll work with all three in this exercise.

Each of the three bars has two small gray buttons at the top and bottom. The top two gray buttons determine the selection range. The bottom two buttons determine feathering, that is, what amount of adjacent values will be included.

Color bar:
Used to select the Hue of the color to be removed.

Sat bar:
Used to select the saturation range of colors to be removed.

Luma bar:
Used to select the luminance range of the colors to be removed.

Edge Thin:
Use to restrict or expand the edges of the selected color.

Softening:
Blurs the edges of a key. Use in very small increments (one to three mouse clicks).

Enhance:
Tries to remove color fringes at the edges of a key by using a complementary color. Use this in very small increments as well (one to three mouse clicks).

4.

The best way to work with this filter is from the top down. Get your color set first, then move to the next row.Don't jump around. Click the eyedropper to select the key color. (The "key color" is the color you want to remove.) Then, click in the dark blue sky near the top-right corner.

Instantly, part of your sky disappears and is replaced by the background.

5.

Next, extend the range of your selected color by clicking the eyedropper again. Hold down the Shift key and click near the middle of the frame.

(Notice how the eyedropper has a very small plus sign next to it? This indicates it is adding to the selection.)

6.

Finally, select the eyedropper again, hold down the Shift key, and click a third time, near the bottom right of the picture.

The light-gray edge between the trees and the sky is very difficult to remove. Still, there's more you can do to improve this key, so move on to the next two lines: Sat and Luma.

7.

In order to see how well your key is progressing, click the Key icon. The Canvas changes from showing the final key, to a mass of white against the background. The white is the "matte," or the visual information you want to retain for your key. Your goal is to get this white matte as solid and firmly edged as possible. (This is far easier to write than it is to do…)

When you are viewing the matte, the Key icon is a black key on light gray background. When you are viewing the source video, the Key is red and the background blue. When you are viewing the final composite, the Key is red on a gray background. Click the Key icon to switch between these three variations.

8.

I've also learned that not all three bars are necessary to pull a good key. In this case, turn off Sat and see if the matte improves. Nope. Better leave Sat on.

9.

Turn off Luma and see if the matte improves. In most keys, leaving Luma off improves it. In this case, due to the noise in the lower-right corner, the key is better with Luma left on.

[View full size image]

10.

Slowly tweak the buttons at the top of the Sat and Luma bars until your matte looks as solid as possible. Periodically, click the Key icon to switch between the Matte, Source, and Final views. Only when the key looks as good as you can make it should you start adjusting the sliders at the bottom. This screen shot shows the values I came up with when creating this key.

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11.

Switch back to the Final video of your key (click the Key icon) and start adjusting the Edge Thin slider. Generally, I move this wildly in both directions until I see if things improve. If not, I leave it set in the middle. If so, I gradually narrow down the range of movement until the key looks as good as it can.

Finally, when everything else is set, click once or twice on the right arrow of Softening. This will blur the edges of your key. Any more than three mouse clicks and things deteriorate quickly. I generally use just one mouse click.

I'll use Enhance when I have a close-up and want to cancel out small blue edges. In this case, it doesn't help a whole lot, so I just used one click.

Before color correction (left) and after color correction (right)

12.

You're done. Render and play your key. The image on the left is my key.

The image on the right is what I came up with after adding color correction. In correcting the image, I pulled down black and midtone levels, significantly boosted the whites, and increased saturation. The image is darker here due to the midtone correction. But this also got rid of the noise in the lower-right corner. You can view my version (without color correction) by playing Seq Chroma key finished.

13.

That's it for chroma key. Save your work and quit if you need a break. Otherwise, keep this project open. There's one more exercise to go in this chapterone of my favorites: creating a travel matte.