With the introduction of the new Fusion tab, DaVinci Resolve 15 has evolved to become more than just a color grading and video editing suite, but also a full-fledged visual effects compositor with some really powerful features.
With the new tools included, multiple VFX and compositing tasks such as a simple sky replacement can be now pulled off with ease, all without having to go into any other third-party application. Seasoned colorist Casey Faris goes through this particular processing using the Fusion integration inside DaVinci Resolve 15.
To start off, you first need to add your footage to the timeline. Place your original clip on the bottom-first layer, and then add the sky image of your choice on top. Keep in mind that when you shoot your video, you’ll need to make sure that the sky is as flat/clear as possible, as the effect would not work with any obstructions (such as clouds) present.
After selecting both clips, right click and choose the option Create New Fusion Clip. You will then be taken to the Fusion tab where you can proceed with merging the two clips. To begin, remove all node connections except for the one between the Merge1 and MediaOut nodes.
Then connect the Sky node to the Merge1 node, making sure to place it in the background. Afterward, repeat the same step with your original clip’s node. Considering that you have setup your project, you will now have to remove the background using a Luma Keyer.
To do so, go into the Tools and under Matte, locate the Luma Keyer. Drag the effect in between your original footage and the Merge 1 node. Go to the Inspector and then select Invert, which is what will make the effect key out the sky rather than the foreground of the clip.
To properly remove the sky from the original footage, adjust the Low Threshold of the Luma Keyer until the sky appears as if it is behind the trees. This will take a bit of trial and error to find the right values, so be patient, experiment with the settings, and see what adjustments suit your footage.
After you’ve adjusted the Luma Keyer, you may notice that your sky clip is too small or positioned awkwardly. This can be easily fixed by adding a Transform node between the Sky image node and the original clip node, then adjusting the position and size to your liking.
The last step before completing the sky replacement effect is to track your footage so that the sky matches the movement of the camera. This can be done by going into the Tools>Tracking and selecting Planar Tracker. Again, just drag the effect between the original footage and Luma Keyer node.
In the Inspector, under the Planar Tracker Effect, change the Tracker setting to Hybrid Point/Area. Make sure you are at the first frame of your clip and then use your cursor to create your tracking area just as shown in the video above. Next, set the Motion Type to Translation, Orientation, and Scale. After you’ve adjusted all the tracking parameters, click the Track Forward button and the software will automatically begin tracking your footage.
When the tracking process is complete, make sure to click the Create Planar Transform button. This will create a node that contains the tracking data. The final step now would be to place the tracking node between the Sky image’s transform node and the Merge1 node.
If you’ve followed all these steps correctly, you should end up with a proper sky replacement, wherein the sky matches perfectly the movements of the camera. To further sell the effect, consider adding some color correction to match the colors of the sky with the rest of your footage.
[source: Casey Faris]
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