Overview of Compositing Using the Chroma Keyer Filter

Although you can use one of several different filters for keying, you often use more than one filter, depending on the qualities of the video clip. In general, the process of compositing two shots together by keying consists of seven main steps, using several different types of filters. For more details, see Example: Using the Chroma Keyer Filter.

  1. Stage 1: Starting with the Color Smoothing Filter

    Apply the Color Smoothing filter to the clip that you want to key the background out of. This filter improves the quality of chroma keys and reduces the diagonal “stair-step” look that occurs in video clips with areas of high-contrast color.

    Use 4:1:1 Color Smoothing with NTSC or PAL DV-25 video sources. (The exception is PAL mini-DV/DVCAM, which uses 4:2:0 color sampling.) Use 4:2:2 Color Smoothing for DVCPRO50 and 8- and 10-bit uncompressed video.

    As you add additional key filters, make sure that the Color Smoothing filter remains the first one listed in the video section of the Filters tab.

  2. Stage 2: Applying the Chroma Keyer Filter

    Now you can apply the Chroma Keyer filter to the clip. Choose a color or level of brightness to key on, and then make adjustments to select the range of color or brightness that most effectively keys out the background, without eliminating the details of your foreground subject, such as hair, fingers, or the edges of clothing. You can also use the Thin/Spread slider to adjust the fringing that appears around your foreground subject, but don’t use it too aggressively.

    Tip: Although the Chroma Keyer filter is the fastest and easiest to use, you may find that the Blue and Green Screen filter, in conjunction with the Matte Choker filter, can perform a closer key on certain clips that have more subtle detail around the edges of the foreground subject. For more information on the controls of the Blue and Green Screen filter, see Key Filters.

  3. Stage 3: Eliminating Fringing with the Matte Choker Filter

    After keying out as much of the background as you can without touching the foreground subject, apply the Matte Choker filter to eliminate any faintly remaining blue or green fringing or pixels surrounding the edge of your foreground subject. Using the Matte Choker filter to eliminate this fringing works similarly to using the Thin/Spread slider in the Chroma Keyer. You may find that, for some clips, the Matte Choker filter works better than using more aggressive settings in the Chroma Keyer, giving you a better chance of preserving as much fine detail around the edges of your foreground subject as possible. Drag the Edge Thin slider to the right to remove faint areas of the key color around your foreground subject and to smooth out the rough edges of your key.

    A second Matte Choker filter can also be applied to fill holes in the foreground subject that appear as a result of aggressive settings applied to key out the background. By dragging the Edge Thin slider to the right, you can fill in semitranslucent areas in your foreground subject, without changing the background areas you’ve already keyed out. For more information about the Matte Choker filter controls, see Matte Filters.

  4. Stage 4: Readjusting the Chroma Keyer Filter’s Settings

    When keying, additional filters you add usually affect the overall results of previously applied filters, so after applying the Matte Choker, you’ll probably want to readjust the Chroma Keyer filter’s settings to take into account the effect the Matte Choker is having. Changes you make to the Chroma Keyer filter’s settings affect what the Matte Choker does, so go back and forth between the Chroma Keyer and Matte Choker filters until you find a balance of settings that effectively removes the background without eating into your foreground subject.

  5. Stage 5: Desaturating the Key with Spill Suppressor Filters

    If you have some slight color spill from the background around the edge of your foreground subject, you can use the Enhance control of the Chroma Keyer to desaturate the color spill so that it’s not noticeable.

    If you have other regions of color spill that appear within your foreground subject—showing through a sheer dress, for instance—you may want to use the Spill Suppressor - Blue or Spill Suppressor - Green filter to selectively desaturate just the key color so that it’s not noticeable. The spill suppressor filters may affect the overall color of the foreground subject, however, so you may need to use a color correction filter to compensate for this effect.

  6. Stage 6: Cropping Out Elements Using the Garbage Matte Filter

    If there are “unkeyable elements” other than your foreground subject that you want to eliminate from the frame, such as props, lighting fixtures, or other undesirable objects, you can use one of the Garbage Matte filters to remove those elements. For more information on using Garbage Matte filters, see Using Mattes to Add or Modify Alpha Channels.

  7. Stage 7: Color Correcting the Foreground and Background Clips to Match

    Even if you shot your background and foreground clips to match one another, it’s unlikely the lighting you used matches perfectly. For this reason, it’s usually necessary to color correct either the foreground subject or the background to make sure the two match. For more information on color correction in Final Cut Pro, see Using Color for Color Correction.

    Tip: When shooting video you intend to composite together using key filters, it’s important to make sure that the direction of the lighting matches in both the foreground and background shots. You can color correct for color temperature, relative brightness levels, and contrast, but lighting direction cannot be altered.

  8. Stage 8: Performing Additional Adjustments to the Background Layer

    Finally, you should spend some time working on the appearance of the background layer. Editing a foreground clip in front of a background clip is just the beginning. There are numerous details you must now consider to make the shot look convincing. For example, the foreground and background of video you shoot in the field are seldom both in focus, so the shot may look more realistic if you put the background out of focus with a blur filter.

    You may also need to consider other strategies for making the background look suitably distant, such as adding a translucent gradient layer to create haze over a landscape or adjusting the appearance of the sky. Adding other keyed foreground elements can also make your shot look more interesting and add depth to the shot you’re creating.