Join Luisa Winters for an in-depth discussion in this video Tips for better keying, part of Premiere Pro Guru: Compositing and Masks.
- When it comes to keying, most of the work needs to be done when shooting the footage. One of the reasons that keying is difficult is because the color that we need to key out is not even. And also because the color is not a pure channel. The best color to key would be the purest one, so for green it will have an RGB value of zero, 255, zero. However it rarely is that because of a myriad of reasons. I recommend bringing a light meter to your shoot so that you can measure the luma.
There are some utilities for your smart phone that you can also use for this. Also, put the subject as close to the camera as you can, and as far away from the green screen as you can. This will make the depth of field cause the background to blur, and therefore be much more even and easier to key. However if you already have the footage and you have no say on how it was shot, there are still things that you can do to improve your keying task.
You can blur the green channel using a channel blur. You can also adjust the luminance of the clip. This will also help you with an easier key. Open sequence 2.6 and place your play head on top of the first clip. This is a smiilar clip to what we had before but with an extra level of difficulty. There's a green cloth that we need to keep in and it is almost the same color as the green background. Let's start the keying process by adding a garbage matte. The four point one should suffice as the subject hardly moves.
Now let's use some effects to make our key a little easier. Let's add a channel blur. For this, I'll just type the word channel. And here's my channel blur. I'm gonna apply it to the clip. In here I'm going to blur only the green channel and I'm going to blur it only a little bit. I believe three pixels should suffice. Now let's add the RGB Curves effect.
For this I'll type RGB and apply the effect to the clip. In here I'm going to up the gamma of the green channel just a tiny little bit. Now I can apply the Ultra Keyer. In here I need to choose my green color. And I'm going to adjust some of these values.
I'll change this shadow value to zero. And now I'll take care of the Spill Suppression. We'll Desaturate this a tad. And I'll change the range a little bit as well. Now I can do a little bit of color correction to this clip. I'm gonna saturate it a little bit. Around 117 is good. For the Hue I'm gonna change it to around minus 16 or so.
And for the luminance I'll make it a little bit brighter, and 104 is good. Now this is obviously not ready because the eyes and the shirt pocket are still transparent. You can easily see that if you change the view to an alpha channel view. You see the pocket and you see the eyes. I'll change it back to Composite. Let's go ahead and add a mask to the Ultra Keyer.
So I'm gonna add this one. And I'll position it on top of the shirt pocket. This is now doing the opposite of what I need it to do, so I will invert it by clicking on this checkbox. Now you can see that the green is maintained in the pocket. This takes care of the green in the pocket, but what about the eyes? Well, we can't really add a mask to the eyes because we inverted the first mask, so a second mask is going to have no effect.
So what we need is duplicate the clip, and I will do that by pressing and holding the alt or option key and clicking and dragging the clip so that it is up. Now I can select this clip and add an opacity mask. I'll click and expand Opacity and add an ellipse mask. Now I can put it on top of the eyes.
Adjust the size. And there we go. Now you can track this clip so that it really fits your needs. As the eyes move, the mask will move with it. We're going to go over tracking a little bit later in this title. Once you're done you can nest these clips and apply color correction to both of them together. So let's go ahead and do that. Select both clips, right click, and choose nest.
Type in a name, I'm gonna leave the default. Click okay and now instead of two clips we have just one. We can now apply a fast color corrector to this one clip and play around with the hue and input levels, so let's go ahead and do that. And we can change the hue a tad. And we can also change the input levels a little bit.
We can even make the clip smaller and put it on the bottom left side of the screen. If you find that you need to adjust the key even after you have nested, go ahead and double click that clip. The nested clips will open automatically and now you can adjust the settings of the Ultra Key however you want. So let's go ahead and do that. Expand your Ultra Key. And expand the Matte Generation.
Let's go ahead and get rid of the highlight by changing the value back to zero. So even when you nest a clip you can always go back and adjust your settings.
- Working with alpha channels
- Keying blue and green screen footage with Ultra Key
- Affecting a moving piece of video with Track Matte Key
- Creating a composite with the Difference Matte effect
- Using Luma key for a brightness-based composite
- Changing the character of footage with blend modes
- Masking effects to certain portions of your footage