Chroma key compositing

This article covers features which are only available in Reeltime Pro

Reeltime Pro allows you to apply a real-time chroma key filter to any live or playback signal and composite the isolated image as a foreground with a background plate that you imported or recorded into the clip library and loaded into a library slot. This article describes creating a green screen compositing with the keyer filter and the overlay layout option in the composite slot and fine-tuning your composite with additional filters such as basic color adjustments and a blur filter.

1. Apply a keyer filter#

If you want to key one or more incoming live signals, you can apply the “Keyer” filter directly in the input slots.

The “Keyer” filter uses a very efficient method to remove green or blue areas in the image signal, which allows it to be applied in real-time without introducing additional latency.

Note: The “Keyer” filter is designed to work only within the green or blue color ranges. If you select another color, the filter may not have the desired effect.

For the best outcome, you can customize your key with dedicated viewing modes and a range of “Matte Control”, “Matte Fill” and “Spill Control” parameters:

  • Mode: Switch between the viewing modes:
    • Preview (=filtered image) and
    • Screen (transparent areas in black / non-transparent areas in white)
  • Channel: Choose the desired target color channel for your key (green or blue)
  • Color picker: Pick a color in the area of the green or blue screen
  • Noise level: Increases the amount of pixels included in the transparent area
  • Details level: Retains more details in the non-transparent areas
  • Amount: Increases the overall red/green (or orange/blue) color difference mask
  • Black fill: Increases the transparent areas of the final mask
  • White fill: Increases the non-transparent areas of the final mask
  • Spill level: Neutralizes color spill in the overall image

Follow these steps to apply a chroma key to your green screen live signal:

  • Select the input slot with the green screen signal.
  • Choose the “Keyer” filter from the “Add Filter” button menu.
  • Use the color picker to pick a greenish color in your green screen background.
  • You can switch to the “Matte” viewing mode to inspect the key.
  • Refine your key with the “Matte Control”, “Matte Fill” and “Spill Control” parameters until your keyed area is black and the foreground is white.
  • Switch back to “Preview” viewing mode to inspect your final key.

The keyer filter will automatically be saved in the upcoming recording. You can change the filter parameters anytime when loading the clip into the playback mode of an input slot or a library slot. Ensure that you save the filter settings when you want to keep your adjustments (with the “Save” button in the filter settings or the associated menu items or Stream Deck controller actions).

Tip: There are menu items and Stream Deck controller actions for copying and pasting your filter settings from one slot to the other if you have more than one camera that captures the green screen.

2. Import background plates#

You can import clips as background plates into your project’s clip library via the movie import function. Note that imported movies need to be in a ProRes codec (as Reeltime Pro uses the built-in ProRes hardware acceleration of Apple Silicon processors to achieve the best performance).

Follow these steps to import your background plates:

  • Select a folder and bin in your clip library into which you want to import your background plates.
  • Choose “File” > “Import Media…” and select the movies you want to import and proceed.
  • Create a library slot or select an existing library slot.
  • Load the imported movies into the library slot and find the most appropriate background plate.
Tip: Use the auto-load mechanism of library slots to quickly toggle between your background plates (by selecting the first clip in the bin and toggling between clips using the arrow up and down keys).
  • When you find the desired background, start playback and enable loop playback if it makes sense.

3. Composite the masked image signal with a background plate#

Now, you can blend your masked image signal with a background plate using the “Overlay” layout mode in a composite slot.

Follow these steps to create your final green screen compositing:

  • Create a composite or select an existing composite slot and switch to the overlay tab.
  • Set the masked image signal (e.g., input slot “A”) as the first source of the composite slot (= your foreground).
  • Set the background plate (e.g., library slot “Lib 1”) as the second source of the composite slot (= your background).
  • Expand the “Overlay” settings in the composite slot and set the opacity to 100%.
    • The “Overlay” settings also allow you to scale the size and offset the position of your foreground. However, please note that those parameters will not be saved in the clip library. If you instead apply filters to your input or library slots you can save your adjustments to your clips.
  • To crop and offset the position of your background and/or your foreground, you can apply a “Crop” filter to the library slot and/or the input slot.
  • To match the color of your background and/or foreground, you can apply a “Color Adjust” filter.
  • To separate your foreground and background, you can soften your background plate with a “Blur” filter.

For live monitoring and recording, you can loop your background plate. If you have set an in and out range in your background plate, it may make sense to enable ranges playback and combine it with looping. After the recording, the background plate remains as is and keeps looping. With the composite slot selected you can keep previewing your composite also during playback.

Tip: You can also arm and record a composite slot together with your input slots, e.g., for convenient recording and playback of a green screen compositing preview together with the individual recordings of foreground and background.

4. Control and sync the sources of a composite slot#

In a composite slot’s viewer controls, you can toggle between

  • The composite’s global controls,
  • the foreground’s viewer controls and
  • the background’s viewer controls.

You can cycle through those individual controls by clicking on the composite slot’s slot name label or using the menu item “Cycle Viewer Controls of Composite Slot” or the associated Stream Deck controller action.

If needed, you can sync the playhead position of your recording with the background plate by switching to the individual controls and changing the playhead position, or the in and out range of the clip.

For example, you can adjust the background plate’s in and out range to match the duration of the foreground clip. Then, you can switch back to the global controls, move the (global) playhead to the in points, and start playback (with ranges playback and looping if desired).

Tip: An info label is displayed when hovering over an in and out range. Inspect the label to see the currently set in and out points and the duration of a range.

Audio monitoring and playback with green screen compositing#

When working with green screen compositing, you will usually have a composite slot selected. Sometimes, you will also switch to an input or library slot. However, you will want to keep hearing the audio of the input slot to listen to the live audio or the original audio that was recorded. Consequently, disabling the automatic audio source selection and keeping the audio pinned to the input slot is recommended.

Audio source pinned to slot “A”

Last updated: July 23, 2024