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Now some plug-ins, notably the green screen plug-in, does not work on one particular variety of Apple and those are Macs that have a Nvidia card and if you own one of those computers, I would encourage you to write to Apple and ask them to update their support for that particular video card and update their driver. Otherwise, you might also too just want to not use the plug-in and want to process the green screen using the nodes, and I really haven't shown you how to integrate the output of the Compositor into the Sequencer, so I thought I would take this opportunity to kill two birds with one stone.
So instead of using this video strip here. I'm going to right-click on it. Press X to delete it, because we can't use it. And what we need to do is come up here and switch of our Compositing desktop layout and add a new empty scene and we are going to call it comp, just because that's short for compositing. Now any scene that we are working in, we have to have a camera. So I have to switch over here real quick to the model layout and choose my comp scene and just add a camera.
It doesn't matter where it's pointing or what its orientation is. It just has to be there so that Blender can render the output. While we are here, we are going to go and switch to using the Composite output instead of the Sequence output. So switching back to our compositing desktop, we are now setup to transfer the output from our Compositing desktop layout to the Sequencer. All of the different settings on those, as far as the size of the video and the frame rate and everything like that, is copied over when we created this scene.
So it's all set up perfectly for us. There is nothing we have to fiddle with over there. So now that we are in our Compositing desktop layout, we just click on Use Nodes. We don't need the Render layer node. So just press X to delete that one when it's selected. I'm going to grab and drag the Composite output node over to the right there, and we want to add an image input node and load up that green screen video. We select the GS_Intro movie and that brings it in. We want to use all 1660 frames of the video and I'm going to click Auto Refresh.
So to pull a green screen you have your choice of Matte nodes. I'm going to use the Chroma Key Matte node and click this color swatch, the eyedropper, and sample a representative image of the green screen background. Now to see how we are doing, I'm going to select the Chroma Key node and add an Output > Viewer Node and we can see we've pulled a pretty good matte. However, there is a couple of issues. One is there is this green halo around her and some colors spill onto her clothes and like that.
Hair is notoriously pretty difficult to pull a green screen from. So we are going to do a little processing on the matte that's used. First of all, this matte is not a perfect black background, so we need to make that a really a sharp black-and-white image. So we need to do some contrast enhancement on that. Also this edge here is pretty aliased, so we are going to have to blur that edge a little bit. And to get rid of that green halo that I just talked about, we are going to have to shrink this mask down just a little bit. To process the matte, I like to use the ColorRamp node, which is in your Converter Group.
I'll thread this now to the Viewer Output. I'll cut my Alpha channel. I don't really need that auto threading for me. And now as I click and drag on my left handle, I'm bringing up the black level. So then a medium gray is in the middle of this ColorRamp. Any medium grays or dark grays even are now mapped to pure black. Next up, I'm probably going to get rid of that green glow and add a Dilate/Erode filter.
And now the Dilate/Erode filter I'm going to cut the thread that was auto-threaded for me, because I want to thread from the-- and I'm going to go ahead and move. Do a little housekeeping here so you can see. I'm going to thread the image output socket to the mask and press Shift+D with this Viewer node selected and drag-and-drop it over here, so I can see the output of my erode. Now as I shrink this erode down let's say 1 or 2 pixels, you could see down here in the UV Image Editor, you could see that mask shrink down just a little bit.
Then I want to blur this edge and so I'm going to with the Dilate/Erode node selected, go ahead and add in a Blur filter. For this particular image, after I thread it in to my, let's say I'm going to reuse this Viewer node to see how I'm doing, to blur the outline of this image. It's in high def. It's 1200X768 pixels, so it's a pretty huge image. I've found that about 5 pixels up and down provides a nice blending that we can use to then combine this image with a background color.
So we are going to add the Color > Alpha Over Node. Then use this blurred Mask to feed the factor socket of the Alpha Over. All we do is we take our Chroma Key Output node and thread it to the bottom socket of the Alpha Over, because it's the foreground image that we want. Then thread the output of the Alpha Over to our Composite output. I am going to select a Viewer node, press Shift+D, and drag it over there, and hook it up to the Alpha Over node and now we can see that we have a very nice neutral white background pulled against her key.
Now we have a little bit of an Alpha Over halo kind of image problem going on here. So I'm going to Convert Pre-multiply, which then smoothes out that blending and blends this foreground image very nicely into the background image. Lastly, I'm going to check my Alpha Over and I want this background to be Alpha 0. And as you can see as I'm dragging over here down, down here in the bottom corner, you can see that the UV Image Editor is actually telling me that it's Alpha 1. So I need to use this Blur output to feed the Alpha channel output.
So what I'm going to do is thread those sockets to there, like that, and now in my Viewer node where the Blur output is black, it creates an Alpha 0, which is exactly what I want here on the background and then as we get her, then it's an Alpha 1. So now I have pulled a great green screen matte using nodes. Now how do we feed that in? Well, what we need to do is first of all just to test render, just to check our results, and boom, here we get the full HD image render of her.
So that's our test render. We've primed the pump now. And now we come back over to our sequencing desktop and with the scene selected, we are going to Add > Scene, and now we have a choice of a couple of scenes. I have a title scene where I have the Garden Spot as a title text object that you can use and play with in Alpha Overing, or mixing into this image. But what we want to do is we want to bring in the comp output and I'm just going drag-and-drop it here to frame 1 and actually I'm not going to bother mousing around.
I'm going to switch over to my Sequence desktop and just in the Start field, click in and type 1. Now we have our video strip brought in, we still have the audio strip and because we haven't changed the timing or anything, the audio and the video will still match up. That's how you use nodes to pull a good matte from this green screen video and how you feed the output of the Compositor into the Sequencer.
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