How to Use Blender Green Screen

Blender is an open-source cross-platform 3D graphics program, but this doesn’t mean it’s a low-rent option. Just like commercial packages like Lightwave 3D, it is also a very capable compositing package. Unlike Lightwave, it is a modern node-based compositor like Nuke or Fusion. It’s not what the software is designed for, but it does a bangup job of green screen compositing, as you will soon see.

Blender green screen uses technique of the chroma key a color is isolated (in our case the green of the green screen), or a particular luminance, it is removed and the area that was occupied by it becomes transparent, thus becoming part of the alpha channel. The transparent parts will thus show the video or the image below, which will thus define the environment in which the subject of the first movie will act.

How to Use Green Screen in Blender

So we need to pull these two elements into Blender and pull a key on the green bits to make the background show through in as naturalistic a way as possible. Blender is a node-based compositor which means the control mechanism is nodes or little LEGO blocks of love which you place on the screen and link with little strings which form your signal path.

Locate the drop-down (it goes up, actually, but you know what we mean) at the bottom of the view, and select “Movie Clip Editor.”

Click the “Open” button and choose and load your green screen footage. (You can also load sequences of images for uncompressed keys in this step if you have the space, and the footage is the right size.)

Once the clip is loaded, go back to the drop-down and select Node Editor.

The screen will be blank, but just go to the bottom of the view and click the middle button marked “Node Tree Type” to Display, and then check the Use Nodes and Backdrop buttons.

Select the “Render Layers” node, and because we won’t need it you can delete it (on the Mac this is the Forward Delete key). Then move the Compositing node out of the way because we won’t need it yet.

Note: to zoom in and out of the nodes, use the centre scroll wheel of the mouse if you have it. To zoom in and out of the images you are working on, use the V and Alt-V keys.

Compositing Nodes

Click the Add menu in the bar at the bottom of the view and select “Input -> Movie Clip.” Select the green screen clip you added in the Movie Clip Editor. This is the input. We have to push this through a keyer to remove the green and make those areas transparent.

Important: in this program flow goes from left to right, so node inputs are on the left of a node, and outputs are on the right of a node.

Now select “Add -> Matte -> Keying” to add a keying node. Also “Add -> Output -> Viewer” to make the output from the key visible. Click on the little yellow dot next to Image output on the Input node, and drag it to Image input on the Keying node. Then drag the little dot next to Image output on the keying node, and drag it to the image input on the viewer node.

You now have to select the key colour, the colour which the keyer is changing to transparent. Click the Key Colour button on the Keying node, and this displays a colour selector. Click the eyedropper, and click on the image in the background somewhere on the green screen.

If you look carefully, you will see that there are some areas which still have a bit of colour and are not fully transparent. You can check this more accurately by dragging the string from the Matte output on the Keying node and linking to the input on the viewer. This is the key you have made. As you can see, the dark bits are supposed to be totally black, and there are still greys showing through. (This is because the source material wasn’t perfect.)

There are many different ways to fix this depending on the shot, but if it’s a reasonably well-shot green screen, all you will need to do is the following.

Adjust the Black Clip slider to expand the amount of greens which turn to black. Then adjust the White Clip to push the whites to prevent them from becoming transparent.

Once you have pure white and pure black, reconnect the image output of the keying node to the image input on the viewer, and you’ll see you have a decent key.

You can adjust the amount of fringing and spill (reflections from the green screen on the model), but generally the keyer does a good job of guessing that for you with a decently-shot green screen.

Adding the background

After this, adding the background is more of the same with a slight twist. “Add -> Input -> Movie Clip,” navigate to your background clip and load it.

To blend the two layers, you have to make a mix of the two clips so that the background shows through the now transparent bits of the foreground.

“Add -> Colour -> Mix node”. Take the output from the background clip, and feed it to the top image input of the mix node. Take the output from the keying node, and feed it into the lower image input on the mix node.

Click the Alpha channel button next to the drop-down on the mix node.

And finally we have our key. The background is way too sharp and makes the green screen footage look really soft and crappy, so we need to soften the background. There is a really nice Bokeh Blur filter in blender for just this purpose to make the background look out of focus and add lots of gorgeous Bokeh blobs.

“Add -> Filter -> Bokeh Blur” and put it between the background clip and the mix. In Blender, if you add a node and place it over a string between two nodes, the string goes yellow, and dropping it will automatically insert the new node into the signal path connecting inputs and outputs.

Finally add an image to the Bokeh Blur for the shape you want the bokeh to be; we opted for a donut-shaped iris pattern.

To render out your video, connect the output of the Mix node to the input of the compositing node we left lying about earlier. It’s okay for this output to be connected to the input node of the viewer, too, as this means we see progress while rendering.

Make sure you are set up to render the right amount of frames at 30fps in the render panel on the far right. 30fps for 5 seconds (the duration of our clip) is 150 frames. Insert 150 where it says End Fr.

Select a place and a filename to output to in the Output panel further down the right-hand side. Then to render, select the info menu bar from the top-left drop-down, and finally choose “Render Menu -> Render Animation,” and the render will begin.

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Related FAQs

How do I get rid of the green screen in blender?

This is achieved by Compositing Nodes: Click the Add menu in the bar at the bottom of the view and select “Input -> Movie Clip.” Select the green screen clip you added in the Movie Clip Editor. This is the input. We have to push this through a keyer to remove the green and make those areas transparent.

How do I get rid of objects in green screen?

This can be done by following these prompts: Select “Add -> Matte -> Keying” to add a keying node. Also “Add -> Output -> Viewer” to make the output from the key visible. Click on the little yellow dot next to Image output on the Input node, and drag it to Image input on the Keying node. Then drag the little dot next to Image output on the keying node, and drag it to the image input on the viewer node.

Conclusion

Obviously, to get the best green screen composites you have to shoot good “plates.” “Plates” are the main bits of the shot that you bolt together in movie visual effects. You have the foreground plate and the green screen bit with an actor filmed in front of a green screen. Then you have the background plate which is the bit you want to show through the green bits of the foreground, making the whole thing look as though the background and foreground were filmed at the same time.