Carnegie Mellon University / Introduction to the Electronic Media Studio (60110-A)

Unit 80

by Golan @ 9:09 am 16 November 2009

Videos used in this unit:


In-Class Exercise: A Composited Scene

In this intense in-class exercise we will learn how to:
— Shoot and record video with a camera;
— Digitize that video into the computer;
— Extract an actor from this video, using chromakeying or lumakeying;
— Composite that actor into a different background scene;
— Regulate time-based properties of video layers;
— Export files suitable for creating a DVD;
— Create a DVD.

Here are the overview steps for the exercise. Detailed instructions are below.

  1. Using a provided video camera, record a few seconds of video of your hand against the keying background. Usually, keying backgrounds are large pieces of colored material: white, black, blue, green, etc.
  2. Using Final Cut, log and capture these clips into files on the computer (“digitizing”). Detailed instructions for this operation are appear below.
  3. Select a background video for your clip. Here are some options: (VJ backgrounds)
  4. Composite your video, using either chromakeying or lumakeying as appropriate, onto the different backgrounds. Which clips work best for which kind of background? How visible is the edge of your keyed layer?
  5. Set the size and position of your layer to change over time.
  6. Export your video.
  7. Create a DVD.


  • Plug in the camera to the firewire port on the Mac.
  • Turn the Camera on, in VCR/Play mode (not Camera mode).
  • Open Final Cut. Don’t forget to set your scratch disks!!!! or you won’t be able to record…
  • Choose File->Capture (You may need to rewind your tape. You can control the camera through the software).
  • Click “Capture NOW.”
  • Press Play on Camera to start the tape rolling.
  • Press Escape to stop.
  • Close capture window.
  • Once you’re done, your captured video clips appear in the Project Window Tab.

A. Quick Colorkeying

  • Bring your foreground clip to the timeline.
  • Position it on the track above your “background video”.
  • After you have trimmed your clip, Double-click on it and select Effects->VideoFilters->Key. (You could also drag this effect onto your clip from the Effects tab.)
  • For green or blue screening, choose either “Color Key” (and use the eyedropper), or choose “blue/green Screen”.
  • For black or white backgrounds, choose Luma key Drag the filter to the clip on your timeline.
  • Adjust the parameters as described more below, this will take some tweaking.
  • Render the video!

B. Fine-tuning the chomakey effect.
Stretch out your Canvas to 100% size as you work. You’ll see a more accurate representation of your work on your Canvas.

  1. Apply Color Smoothing filter (ie drag the filter to your clip onto the clip in the timeline) Click on the Filters tab and then go to Effects>Filters>Key>Color Smoothing 4:1:1 (for ntsc footage only) The Color Smoothing filter will smooth out most of the “jagged edges” around your chroma keyed subject.
  2. Apply Chroma Keyer Effects>Filters>Key>Chroma Keyer.
    Now go about removing most of the blue or green background.
    For this, you’ll use Chromakey filter.
    In its tab select Visual, then select Color Eyedropper.
    Click on the Select Color Eyedropper and then click on a portion of blue or green screen near the subject.
    A good portion of the background color should fall away.
    Click on the Select Color Eyedropper once more and then hold the Shift key down.
    Return to the Canvas and click on a remaining chunk of blue or green.
    Continue this process until most of the blue or green is knocked out.
    You may want to zoom into the Canvas to select the smaller areas of green or blue with the Eyedropper.
    It’s OK to leave some of the blue or green around the subject for your edge detail.
  3. Open the tab for the chromakeyer. Look at the Visual tab and the Numeric tab: Adjust the following parameters until you see what you want: Color Control Strip Saturation Control Strip Luma Control Strip. Edge Control
  4. Check your keyed subject against black, white and checkerboard backgrounds. Go to the top View>Background and choose a color or checkerboard.That way you can more easily detect if there are any remaining areas of the background that have not yet been removed.
  5. Apply and adjust Green Spill suppressor filter, this will remove any green spillover on the subject.
  6. Render.
  7. Export, using Quicktime Conversion, a 640 by 480 .mov that has H.264 compression…

Burning a DVD using iDVD

  1. Open iDVD
  2. Create a new project
  3. Pick a background
  4. Go to File>Import>Select your video
  5. Drag the video or an image you like to the menu for a looping background clip
  6. Type a title in the menu, it will act as a play “button.”
  7. Hit Preview, ie press play or enter and then click on the title, if it works exit preview
  8. File>Burn DVD Insert DVD Let it burn Check and make sure it plays.

How to get the best results with a green screen!

These suggestions for chromakeying are adapted from Ken Stone:

  • Use the highest quality camera and acquisition format possible (Ideally a 3CCD video camera).
  • Use larger CCD chips, and quality lenses if possible. This may not be possible given the equipment currently available to you, but keep it in mind for the future. For work you do in the School of Art, you are probably using miniDV.
  • Pay special attention to the lighting. The background should be lit as evenly and flatly as possible. Strive for no shadows or creases in the backdrop.
  • Place your subject as far from the backdrop as possible, so they will not cast any shadows onto it. Another reason for this is so that the backdrop will not create “spill” (reflected green or blue light) onto the subject, making keying more difficult. The cameraperson should be the about the same distance from the subject as the subject is from the wall.
  • Smooth down any flyaway hair and avoid any fringe in the clothing. Avoid jewelry, like earrings and necklaces that might reflect blue or green or that might be difficult to key due to the relative size of the objects.
  • Make sure that the actors are not wearing green if you are doing a green screen shot (or blue if it is a blue screen shot). Black is also not a good choice, since it tends to absorb spill.
  • Zoom in! It actually benefits us to use a lower depth of field. A camera zoomed in from a distance has a far lower depth of field, which means that very little beyond what the camera is directly focusing on will be in sharp detail. And remember that we actually don’t want sharp detail in the screen. Detail (generally) means contrast or change in value, and we want the smoothest, most even green background we can get. So an out-of-focus background that nonetheless has the right luma and chroma value is better than a sharp focus background where the camera records every tiny shadow and bump.
  • Avoid moving the camera during shooting, ie no pans.

For today’s in-class assignment you are going to make Clones, using the videos provided with several techniques:

  • Cropping
  • Masking
  • 4 or 8 pt garbage mattes

Please note that the terms Mattes, Masks, and Keys are often interchangeable. They achieve a similar effect.
A. Cropping

  1. In Final Cut, Drag both left and right videos on the timeline. Place one directly above the other. Double click on the video on top on the timeline.
Viewer>Motion>CropAdjust: left, right, top or bottom
  2. Drag the third video to the timeline. Crop.

B. Masking

  1. Drag the third video, under the table, to the timeline. Although you can crop this in, you can also use a Matte called Mask Shape.
  2. Effects menu > Video Filters > Matte, select Mask Shape, drag onto the clip. Double clk on the clip in the timeline.
  3. Click on the Filters tab. There are four options for the shape of your Mask from the Shape drop down menu: Diamond, Oval, Rectangle, and Round Rectangle. Horizontal and Vertical Scale will size the Matte. Click on the ‘Center’ button (+) then click in the Canvas window where you want your Matte to be centered.

C. 4 & 8 point Garbage Mattes

The Four and Eight Point Garbage Mattes work in an identical manner. The Eight Point Garbage Matte has four additional crop points that can be set. (For the last clone you will use the fourth video (on_top_of_table)

  1. Drag the 4 point Garbage Matte filter from the Effects>Video filters>Matte>4 piont Garbage Matte. Drop it on to the clip on the Timeline. Park your playhead over the clip. Double click on the clip to load into the Viewer, click on the Filters tab.
  2. Now you can see the clip in the Canvas on the right and you can adjust the matte using the “Corners.” Clk the + for point 1, Go the canvas, you will see a red +. With your mouse move this to wherever it should be. Clk the + for point 2, Go to the Canvas and look for the red + for point 2 and adjust, do this for all four points.

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