Working with the Chroma Keyer Filter

Despite its name, the Chroma Keyer actually uses a combination of chroma and luma keying to achieve a good key. Using the Chroma Keyer, you can create a key using any range of color you want, including (but not limited to) the usual blue and green. You can also fine-tune your composite by adjusting the color value, saturation, and luma ranges used to define your key, together or separately. For example, if you only want to perform a luma key, you can turn off color and saturation. Even when performing a color key, you’ll get superior results by manipulating the Color Range and Saturation controls separately.

The Chroma Keyer filter is available in the Key bin, within the Video Filters bin in the Effects tab of the Browser. When you add this filter to a clip, a Chroma Keyer tab appears in the Viewer.

Specifying the Type of Controls to Use for the Chroma Keyer Filter

The Chroma Keyer has a set of visual controls, as well as standard numeric interface controls. The visual controls are those you’ll probably use most often, but you can switch between the two.

To use the visual controls
  • In the Filters tab, click the Visual button next to the Chroma Keyer filter.

    The visual controls appear in the Chroma Keyer tab.

    Figure. Chroma Keyer tab showing the Copy Filter controls and the visual interface.

Note: The visual controls also include several Copy Filter controls. For detailed information on these controls, see Working with the Copy Filter Controls.

To use the standard numeric controls
Do one of the following:
  • In the Chroma Keyer tab, click the Numeric button.

    Figure. Numeric button in the Chroma Keyer tab.
  • Click the Filters tab.

    Figure. Filters tab showing the standard numeric interface of the Chroma Keyer filter.

Visual Controls in the Chroma Keyer Filter

The following controls appear in the Chroma Keyer tab in the Viewer.

Figure. Controls in the Chroma Keyer tab.
  • Enable/Disable checkbox: Make sure there’s a checkmark in this checkbox for the controls you want to use. This lets you add or remove color, saturation, or luma from the criteria used to define a key.
  • Reset button: Click to restore the Color Range, Saturation, and Luma controls to their default values. Shift-click the button to reset all three controls at once.
  • Color Range control: Allows you to fine-tune the range of color that you want to key on.
    Figure. Color Range control showing top and bottom handles and the color gradient.
  • Top handles: Let you select a larger or smaller range of colors that are keyed, based on the original colors you selected with the Select Color eyedropper tool. These handles correspond to the Width control in the Key on Chroma area of the filter’s numeric controls.
  • Color gradient: Drag left or right within the color gradient to shift the overall hue of the color range you’ve set with the top set of handles. This corresponds to the Center On control in the Key on Chroma area of the filter’s numeric controls.
  • Bottom handles: Allow you to define the tolerance of your key. These handles correspond to the Softness control in the Key on Chroma area of the filter’s numeric controls. Use these handles to gently eliminate additional fringing from your key while attempting to preserve fine detail around the edges of your foreground subject.
  • Saturation control: Allows you to adjust the degree and range of saturation that contributes to defining your key. The top and bottom handles work the same as those in the Color Range control. Drag left or right within the gradient to move all four handles simultaneously.
  • Luma control: Lets you adjust the degree and range of luma that contributes to defining your key. The top and bottom handles work the same as those in the Color Range control. Drag left or right within the gradient to move all four handles simultaneously.
    Figure. Select Color eyedropper, View Final/Matte/Source button, and the Invert Selection button in the Chroma Keyer tab.
  • Select Color eyedropper: When you click this button, the pointer turns into an eyedropper you can use to select a color from a clip in the Video tab of the Viewer or in the Canvas.

    Clicking this button and then Shift-clicking with the eyedropper in the Viewer or Canvas allows you to select another region of the background screen that wasn’t keyed out by your first use of this control. This broadens the range of colors to be keyed out and enlarges the keyed-out area. You can do this repeatedly to broaden the range of keyed-out color to include shadows or highlights on the background screen, if necessary.

  • View Final/Matte/Source button (the key): This button has three states: Final, Matte, and Source.
    • Final: The default state (a key against a gray background) lets you see the end result, the effect happening within the keyed area.
    • Matte: The second state (a black key against a white background) displays the key itself as a grayscale image, so you can fine-tune the key without being distracted by the image.
    • Source: The third state (a key against a blue background) shows only the original video image.

    Important: Before you render or output video using the Chroma Keyer filter, make sure that the View Final/Matte/Source button is in the Final state.

  • Invert Selection button: Click this button to invert the key you’ve defined. For example, if you’ve set up a key based on the color of a green car and used a grayscale copy of the clip in the background so that the car is grayscale and the background is color, clicking the Invert Selection button reverses the key so that you see the car in color and the background appears in grayscale.
    Figure. Edge Thin slider, Softening slider, and Enhance slider at the bottom of the Chroma Keyer tab.
  • Edge Thin slider: Drag this slider to make the size of the currently defined key larger or smaller. This can help you remove unwanted edging around your subject.
  • Softening slider: Use this slider to blur the edges of your key to make it blend better with the background image. This can come in handy to soften the jagged edges that sometimes develop when chroma keying material captured with the DV codec.
  • Enhance slider: Adjust this slider to selectively eliminate any spill of the key color that may be visible in the semitranslucent areas of your key, such as edges and holes.

Example: Using the Chroma Keyer Filter

The following example illustrates a typical use of the Chroma Keyer filter.

To apply the Chroma Keyer Filter
  1. Edit the green-screen clip you want to key into the Timeline.

    If you wish, you can use a superimpose edit to place the green-screen clip over a clip you want to use as the background.

    Tip: If you edit the clip into track V2 of the Timeline, you’ll have room to insert another clip as the new composited background.

  2. Apply the Chroma Keyer filter to the green-screen clip you just edited in.

    For more information, see Applying a Filter to a Clip.

  3. In the Timeline, double-click the green-screen clip to open it in the Viewer; then, in the Viewer, click the Chroma Keyer tab.

    Note: In this example, you won’t use the numeric controls that appear in the Filters tab.

  4. Click the Select Color eyedropper to pick a color in the clip to key, move the pointer to the Canvas (it turns into an eyedropper), then click the desired key color. Choose a color that’s fairly close to the edge of your foreground subject, so that the area near the subject is the first area of color you key out.

    The color range you select with the eyedropper becomes transparent in the clip.

    Figure.  Canvas windows showing the results of the first key color with the eyedropper tool.

    Next, you want to expand the keyed area to include regions of the background that weren’t immediately eliminated by the first key.

  5. Click the Select Color eyedropper, and in the Canvas, Shift-click another region of the background you want to key out to enlarge the region of transparency.

    Figure. Canvas windows showing the results of keying out another region by Shift-clicking with the eyedropper.

    You can perform this step as many times as you need to. The goal is to eliminate as much of the background as you can without affecting the foreground subject. If you start encroaching on the outline of your foreground element, you’ve gone too far and should undo. It is not necessary to remove all the background fringe around your foreground subject with this step; you should focus only on eliminating the major areas of the background screen.

    Tip: As you key out more and more of the background, you may find it helpful to use a different background in the Canvas. The Checkerboard 1 and 2 backgrounds may make it easier to see fringing areas of your picture that aren’t yet keyed out. You can also use other background shades and colors to compare the key effect against a lighter background.

  6. If necessary, adjust the Color Range, Saturation, and Luma controls to remove more of the key color from the background and eliminate more fringing from the foreground layer without affecting the foreground subject.

    The top handles adjust the overall range of hue, saturation, or luma keyed out, while the bottom handles blur the difference between the range of color that’s keyed and the range of color that isn’t.

    Note: You should remove the majority of the green screen using the top handles, but stop at the point where there’s still some fringing around the areas of fine detail in the foreground subject. This is the point where you should start using the bottom handles to expand the keyed area more softly. It is not important, at this point, to completely eliminate this fringing, only to make sure that it’s soft and translucent, rather than pixelated and solid.

    Figure. Chroma Keyer tab and Canvas showing the majority of a green background removed.
  7. Depending on how the edges of your foreground subject look, you may want to make adjustments using the Edge Thin slider. The Edge Thin slider allows you to shrink the alpha channel created by the Chroma Keyer to begin to eliminate the light fringing that remains around the edges of the foreground subject.

    Figure. Chroma Keyer tab and an image in the Canvas before adjusting the Edge Thin slider.
    Figure. Chroma Keyer tab and an image in the Canvas after adjusting the Edge Thin slider.
  8. An optional step at this point is to use the Softening slider to blur the edges of the foreground subject. This is especially helpful if the edges of your foreground subject look rough because of compression artifacts that appear as blocky edges around your foreground subject. Don’t overdo this adjustment, as you could start to lose details in the subject that you’re trying to preserve.

    Figure. Before and after images that illustrate the results of adjusting the Softening slider.
  9. If you still see light fringing at this point, or if you were forced to use settings so extreme in the Chroma Keyer that some of your foreground subject was eaten away around the edges, apply the Matte Choker filter. After you apply the Matte Choker filter, adjust the Matte Choker’s Edge Thin and Edge Feather sliders. This is the point where you should work to eliminate all the background fringing.

    Moving the Edge Thin slider to the right further shrinks the alpha channel around the foreground subject, eliminating still more fringing. Moving the Edge Thin slider to the left expands the alpha channel, allowing you to replace areas of the foreground subject that were lost. The Edge Feather slider allows you to blur the edges even further, if necessary.

  10. If you’re satisfied with your key, but there is some color from the background that is spilling onto the edges of your foreground subject, go back to the Chroma Keyer tab in the Viewer and adjust the Enhance slider to desaturate this spill so that it’s not noticeable. Don’t move the Enhance slider too far, or you may get undesirable coloration in the edge of your subject.

  11. If there’s still more colored spill on your foreground subject that the Enhance slider didn’t eliminate, apply the Spill Suppressor filter.

    The Spill Suppressor filter desaturates color spill that may appear anywhere on the foreground subject, not just on the edges. For example, a little of the background color may show through translucent areas of the foreground subject, such as wispy hair or sheer clothing. Once you’ve applied the Spill Suppressor filter to your keyed clip, adjust the Amount slider to determine how much to desaturate the spill color in the foreground image.

  12. To eliminate any unwanted elements that didn’t get keyed out, such as rigging and lights around your subject or the edge of the blue or green screen itself, use the Crop parameter controls in the Motion tab of the foreground clip to cut those elements out of the picture. If the area you need to crop is irregular, you can apply a Garbage Matte filter, instead.

    Figure. Canvas window showing an image cropped on both sides to remove extraneous elements.
  13. Finally, you’re ready to insert the background image. Make sure that the clip you’re editing into your sequence to use as the background image appears in a video track below the foreground clip being keyed.

    Figure. Canvas window showing a composite image of a woman against a new background, and the Timeline showing that the background image is placed on the track below the foreground clip that was keyed.
  14. To really make the foreground and background look as if they were shot together, it may be necessary to perform additional compositing steps such as blurring the background to make it look out of focus, color correcting the foreground subject to have the same color temperature as the background, or using motion effects to move the foreground subject. Even with a successful key, these are the details that make a composite look like a finished shot.

    Figure. Canvas window showing the resulting composite image of a woman against a different background.