Never Retrack Magic Mask
Magic Mask 2 in DaVinci Resolve 20 is an AI rotoscoping tool. This tutorial demonstrates how to render out the matte to avoid re-tracking issues that occur when duplicating timelines or changing resolutions, which often cause the Magic Mask cache to be lost or invalidated.
Step 1: Ensure Clip and Timeline Resolution Match
Verify that your clip and timeline resolutions are the same for consistency.
Example: If your clip is 3840x2160, your timeline should also be 3840x2160.
Step 2: Duplicate the Clip
Hold ALT (or OPTION on Mac) and drag the clip to create a copy.
Add SHIFT while dragging (ALT/OPTION + SHIFT) to keep the duplicated clip perfectly aligned horizontally.
You can confirm alignment by checking timecode overlays.
Step 3: Apply Magic Mask on the Color Page
Go to the Color page.
Select the Magic Mask tool (person icon in the tools panel).
Ensure the overlay (red onion skin) is on.
Click a single point on the subject's body with the eyedropper.
Click "track forward and backwards" to track the mask.
Change the Clip White Value to 99 to fully solidify the inner core of the Magic Mask
Step 4: Connect the Alpha Output for Rendering
Disconnect the green output from the Magic Mask node.
Connect the blue output of the Magic Mask node to the green rgb color page output. This routes the mask as black and white color information.
Switch to the Edit page (the display might temporarily turn blue, but will revert).
Step 5: Render in Place
Right-click on the clip in the Edit page.
Select "Render In Place."
Choose a suitable format like ProRes 422 (plenty for a black and white grayscale matte).
Consider changing the file name to something like "roto" to auto-increment numbers.
Ensure "render at source resolution" is selected.
Click "Render."
Choose a location to save your rendered alpha channel.
Step 6: Composite and Smooth Edges in Edit Page
Modifying Magic Mask Edges: You can smoothen sharp edges of the magic mask using a blur, even though there's no alpha channel initially. A Gaussian blur can effectively smooth out the magic mask.
Pre-Multiply Images: To cut out an image underneath using the blurred magic mask, take a copy of the original image and place it above in the foreground.
Blending Modes: In the inspector, set the composite mode for the foreground (the actual image) to "foreground" and the matte (the blurred black and white image) to "luma." The color image should be on a video track above the matte.
Result: Disabling the duplicate clip underneath reveals the cut-out image, where the alpha channel (the blurred mask) has been applied.
Creative Uses: This technique allows you to modify the alpha channel separately, such as placing text behind objects to make them appear to live in the scene.
Compound Clips: You can also select both clips and make them a compound clip for further manipulation.
