Green Screen


I wanted to try the example our teacher gave us the week before. So I started by selecting (using Ctrl+Shift) the darkest and brightest color of the plate. Then I created two different Constant nodes and merged them together in order to get a single background color. This passage was definitely pointless since the shades are not so different and quite undetectable.

So: since the character in the foreground has a big amount of hair and the furniture is quite blurred in the background, I decided to use an IBK node. This node is one of the best Nuke’s keyers for getting details out of fine hair or blurred edges.

To finally separate the character from the green screen, I added an IBKGizmo, to adjust red, blue, and green for despill fix.

To be fair, I played a lot with the Gizmo. I thought I would be able to match the two plates by using this node, but just later I realized that I should have used a grade node to modify the video’s color parameters in order to make it look similar to the background image.

So that’s what I did.

After having connected the IBK Gizmo node, I decided (even if pointless) to connect the two Constant nodes to the IBK node, by using a merge in minus, to isolate the color problem.

Finally, I added a Grade Node and modified some parameters.

Then I added a Roto to avoid that something, apart from the character, would appear in the video.

Then I added a Blur and merged it to the plate’s alpha with operation in mask [Merge (mask)].

Last but not least, I tracked the video. So I selected the plate, inserted a Tracker node, and put 4 track points. At first, I put those points both on the left and on the right, then I realized tho, that close to the video’s end, the character runs toward his right, and when I baked the match-move track, the background image was not matching the video’s move.

So I did it again, but properly this time:

I tracked four points on the left, then I exported a Transform (match-move baked) node and connected it to the background image. Before this, I added a Transform node to the image.

Final Result

As you can see tho, the match-move is still not working properly.

Basically what happened is that I forgot about setting the correct frame before tracking the points and baking the node.

Therefore, I made another track node; decided to track just the lights behind the computers on the foreground; set a frame into the Tracker dialog box “Transform”, and eventually play the tracking. Finally, you’ll create another Match-move from the tracking and connect it to the background image.

This is the final result.

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