Using Blender 2.8 it is possible to create a “green screen” video. Essentially you record a video in front of a green screen then superimpose that video over another background. To do this in Blender is fairly simple but you have to know what you are doing. It’s certainly not intuitive.
This picture shows the compositor window it’s important to understand that Blender has many different work benches in which you can manipulate “things” The compositor window allows us to take the source and apply nodes making it possible to filter out the green screen. This blog is just showing the very basic process of making a green screen video. It’s not intended to be perfect and much of the “tweaking” will depend on the final video used.
Here you can see three work benches are open the video editing, the rendering, and the compositing. You can switch between these work benches but for now it’s only necessary to use the compositing work bench. If the compositing work bench is not open, click on the + to the right and select compositing.
When you check the use nodes box (see previous picture) you will be presented with a rendering node and a composite node. You can delete the rendering node as we are not working a rendering as our source. To delete it, right click on the rendering node and select delete. Instead we are working with our green screen movie. Click add then input from the menu and insert a Movie Clip node. To place the node just move the mouse and left click in the position you want it to stay. It doesn’t really matter where you put it but input is usually left to right. At the bottom of the node you can see a file search box. Click that and select your green screen video. Of course at this point the green screen video is just something in front of a green screen that you can see, no magic has been applied.
Now add a keying node. You can find that under the Matte menu item. You will see that the keying node will allow you to select many different adjustment factors. More on this later.
Now connect the image output of the green screen movie clip node to the image input of the keying node. Don’t adjust anything yet, there are more nodes to add that will make the adjustment easier. Now add an Alpha Over node, you will find it under the color menu. Connect the image output of the keying node to lower image input of the Alpha Over node. You will see why later.
Finally add viewer node now connect the image out from the alpha over to the image input of both the composite node and the viewer node. This will show you the green screen picture in the background. You can adjust this image to make the green screen disappear. To start you will need to go back to the keying node.
Here you can see an item called Key Color. Click on the color and choose the color picker (pipet) and select a darker portion of the green screen in the video image. This will set the key color so that Blender will try to remove it. Now you can tweak all the settings in the keying node to try and make the green screen disappear. – You should wait for the change to render before you try another tweak. Eventually you may add other nodes to assist with removing the green screen but for now, let’s keep it very simple. Once you have the green screen removed (in my example it’s not quite gone but I don’t want to be perfect here just get the principle worked out.Now we can add a second movie clip node, this will be our background. It can be a static image or another video. The choice is yours. Once you have added the node use the file selector to insert the media you want to use. Make sure that it is large enough to fill the background. If it is not adjust it before you use it.
Once you have the media loaded in the second movie clip node just connect the output of that movie clip node directly to the upper image input of the Alpha Over node. This should put your image in the background.Before you render the video you need to make sure you have everything set up properly. The output should look like the picture above. Select an output folder and ensure you have ffmpeg video selected or it will just render frames. Select RGB for color output and an MPEG4 container. Make sure your end Frame is the end of the video you want, too short and you won’t get it all, too long and you will have a lot of black. And finally, and most importantly. Blender will by default render the sequencer (video editing work bench) you need to select just compositing in the post processing. Then just render the animation. I normally render the image first just to make sure it’s rendering what you want to see. Rendering takes a while, go get a drink and come back later and you should have a video in the output folder that you selected. You can take that video into the video editing work bench and manipulate it like any other video.
If you want to use a box matte to remove areas of the video that are not on the green screen. Ensure you connect to the garbage input on the keying node. The box matte node should connect right after the movie clip node and before the keying node.
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