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Chroma Keying DV in Sony's Vegas

Step by step through the process By Keith S. Kolbo

As budgets have become tighter and tighter, and the technology has improved, chroma keying in video has become commonplace. It is said that chroma keying in DV is unacceptable. New specialized tools have greatly improved the chroma keys in DV, but with a little understanding of DV and the right process, you can get good results with your NLE. We are going to step through the process of producing a quality chroma key with Sony's VegasŪ NLE. You may find that many of the tools used in Vegas are available in your NLE. If so, the process should be very similar.

We are going to start with a nightmare for raw footage. The talent has light blond hair that is fine and flyaway. She is standing in front of a wavy curtain with plenty of shadows. Notice the hot spot behind her and how the picture darkens at the top and bottom. We have one thing going for us, she is well backlit.

DV chroma keys usually have a number of problems, but the most annoying is the blockiness of the key (see the purple arrow below). The jaggies are caused by the nature of the color sampling in DV. Not every pixel has full color information. This means that where one color begins and another ends can be in big blocks. The color sampling in DV is 4:1:1. Don't worry if that does not mean a lot to you, we are going to go through the steps to deal with it.



Your first step to create your chroma key is to place your source clip on the timeline. Now drag the Chroma Blur video effect onto the event. When the dialog opens, select a medium blur to start. When Vegas modifies video, it decompresses the video into a 4:4:4 color space. The best way to think of it is that this gives color information to each pixel. The Chroma Blur smoothes the colors in that space. Now instead of cutting out the object in big blocks, you can cut it out in smooth almost one pixel lines. You can see the difference in the pictures.

Next drag the Chroma Key video effect onto your clip. Trust me on this one, but to start, turn off the effect by un-checking the box in the effect chain. (see yellow arrow below) Now click on the eyedropper (red arrow below). You are now going to select the color to key on, but you are not going to select just one color. You are going to select a range. Draw a large box by clicking and dragging with the eyedropper in the video preview window.




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Related Keywords:chroma keying, DV, Sony Vegas, NLE

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