Join Lee Lanier for an in-depth discussion in this video Removing green screen with Primatte, part of Learning Fusion 7.
- The very common task of Compositing, and Visual Effects Compositing, is removing Green Screen, or occasionally Blue Screen. Idea there is to tack to the color there, like green, and convert it to Transparency Information, where it updates the Alpha Matte that allows you to place the foreground, the thing you save over some new background. And generally you use a Chroma Key Tool, to remove a separate color. Fusion comes with the Primatte tool for this purpose. This is a nice tool that allows you to step through the process.
Let's give it a try. Once again I have Green Screen footage of an actress, that we've used before. and this is loaded up into Project Eight dash Three. With the Loader selected, I'll go get a Primatte Tool. Tools, Primatte, Primatte V5. I'll go ahead and look at the output of that by pressing two key Once the properties are visible in the Tools tab, you'll see a number of buttons. These buttons are great because they're ordered in such a way that you can roughly remove the Green Screen, and then continuously refine it until you get a good result.
In fact the first button is very useful, Auto Compute. This will automatically detect the background color the color of the screen like the green, remove it as best as it can, while maintaining the foreground, and this gets you quite far with a single click of a button. Auto Compute, and there we go. You'll see that most of the green is removed. You can also look at the Alpha Channel to see the result. we'll go ahead and press the A key and there is the Alpha, then zoom in. So black represents Transparency, white Opaqueness and grey Semi-transparency.
That's not perfect but it's gotten pretty far. Now the additional buttons you can use to improve the resulting matte, and again these are roughly in order. For example there is grey over here on the left, due to a shadow. Let's remove that. I'd like to turn that into Black, transparency. The next button is Select Background Color, this is where you can select the green if you want to. I can go ahead and skip that and go straight to Clean Background Noise. Now whenever you click any of these buttons here, your mouse has a special Eye Dropper, and you can click, or click drag in the View, either in the Color View or the Alpha View, to try to attack a particular problem.
In this case, if I click drag over the Noise area of the Background, that will convert to Transparency. You can see it gets much more black. Now there's still a part of the foreground too, the foreground also has grey , again it's semi-transparency. The next button will allow me to clean the Foreground noise. Clean Foreground Noise, click or click drag over the problem areas, and it will start to become more and more white. Now if I'm too aggressive with that I might start to expand the edge of the matte, the edge of the actress outward so I pick up some of the green background.
Let's take a look at the Color Channel again, and C key. At this point it's looking pretty good, however there is a huge amount of green in the hair, let me zoom in again. And this is due to the green light reflecting off the green abracor, the green screen, and mixing with her hair color. The next button is designed to remove Spill Color, Spill Sponge. Click that, then I can click drag over the greenest areas of her hair, and that will start to remove that green. Now when you remove green, it's going to replace it with additional Red and Blue, so if I go too far I might get some purplish colors going on so it's a big improvement already.
Now as we go further and further with this buttons, I get more and more refined. For example the next one, Matte Sponge will restore part of the foreground matte, so I can click along the edge. Now if I'm not careful, I might actually bring back some of the green, but that button's really for restoring a part that you might have lost in the foreground. Keep in kind that any time you sample the screen with one of these buttons, you can always undo it a step back, in fact I'll just press Control or Command Z here to undo that last Matte Sponge application.
Going through there's Restore Detail, this restores fine detail on the edge of the matte. It's going to be fairly subtle but some of the fine hairs start to reappear. I want to skip ahead to these final six buttons here. You'll see there's Plus signs and Minus signs, this is where we restore something with the plus, or remove it with the minus, and these are very subtle fine tuning steps you can take. For example if you remove too much green and the color starts to look funny, you can restore the Spill color.
It's going to be a subtle change but some green will start to come back in. Opposite of that, you can remove the Spill. You can also restore the Foreground Matte, or remove some of the foreground matte, restore some edge detail, or remove some edge detail. Now you may not need to use these, these will be very subtle incremental steps when you sample. A lot are there for fine tuning. Okay, so we're looking pretty good now, I'll zoom back out. It's not perfect though, we have the tracking marks left over, there are some wrinkles from the Green Screen that still appear, we still have green chaps in our hair, and maybe the hair edge could be improved.
Now I may not be able to get it perfect with this single Chroma Key tool like Primatte, but the goal is to get it most of the way there. And the we can use other tools to do additional refinements. Now if you're really curious about the true quality of this Green Screen removal, you really should put a new background behind the actress. If you have a new photo, a new image sequence, new video, merge it with this result. Now if you don't have anything handy, that's going to be a new background, you can always test it with a solid color, let me show you that. With nothing selected, I'll go up to Tools, Creator, and Background.
This will be a solid color generator. You can change the color right here, through the Color Picker and then Merge it together with the Green Screen footage. Tools, Composite, Merge. In fact it's this tool selected, Background selected, then I'll make this connect to the background. And then I can connect the Primatte to the Foreground, and take a look at the Merged Tools output, there we go.
Now one problem is the background has a default size, if I go to the Background Image tab I can change the Resolution to match the video footage, so 1920 by 1080, there we go. so this plays in this colored background, I can see the quality much easier, I can see where the problem areas are. and if I had the new background, you know the photo or the image sequence would be easier to tell if it's going to work or not. Now again, there are a few extra steps you need to take here to clean this up but we're going to do this in a later video So going back to the Primatte tool you can see it offers a very straightforward means of removing green screen through the Auto compute button and the the buttons that lie in the sample, the various pixel values which are actually ordered in a logical fashion.
- Basics of the Fusion interface and general workflow
- Creating tool (aka node) networks
- Working with transforms
- Using expressions
- Masking and rotoscoping
- Altering outputs with color correction and effects
- Compositing in 3D
- Motion tracking
- Keying with Primatte
- Rendering to disc