Join Eran Stern for an in-depth discussion in this video Handling tricky key shots, part of After Effects Tips and Techniques: Compositing and Effects.
- The to-go effect for green screen or blue screen footage in After Effects is usually Keylight, this effect was developed by The Foundry and it's bundled with After Effects for many year now. It's a one-stop shop for Keying, fixing matte problems, Color Suppression, and even Color and Edge Correction. It's also the only place in the software that I know of that the word color is spelled with a "u", this is of course because The Foundry, as you may have guessed, is based in the UK.
Anyhow, in this movie I want to take you through what I consider the most important steps when coming to key footage inside After Effects, specially when the clip is tricky or not shot so well. For that we are going to use this slow motion, green screen footage of this couple dancing. Just so you know here is a quick peek of the background layer that we are going to use so you can get a sense of where I'm taking this.
Now, let's bring back the couple and select them, and then I'm going to go to the Effect menu and under Keying I'm going to select Keylight. Now, this shot, which was took under good condition, looks like it's not going to be big challenge for the Keylight effect, however we can see that we have a lot of green spill around this area, and also this semi-transparent area of the dress, and the little details of the hair may introduce problems.
First, we need to make sure that we are actually using the correct green color to start with, so I'm just going to start by clicking on the eye drop over here, and then before clicking somewhere near the talent, somewhere very close to their body, I'm going to hold down "cmd" on the Mac, "ctrl" on the PC. If you are going to take a look at the icon of the Picker over here, and this is without the "cmd", and with the "cmd" key, you can see that it got a little bit fatter meaning that when I'm going to click it will actually calculate the radius of five pixels around the area that I've used in order to capture more colors and not just the specific point or the specific pixels that you clicked there.
Now, the next step is actually going to the Status View and this will show you, using three colors, what's considered to be complete transparent, which is the black area over here, complete opaque, which is the white, or semi-transparent area over here. Now, in this case, I think that we might want to take the screen gain just a touch up in order to create what I'm thinking to be a better selection, a better a key, and this is just shifting the gain.
Now, sometimes this will not be enough so I also recommend to click on this green color and this will open up of course the Adobe Picker Color, and I'm just going to move it out of the way, and then I'm just going to scrub the color over here to somewhere maybe like this, which looks to me like a better green selection. So when I'm clicking Okay over here and then move to the Screen Matte, which will show me the actual matte, I can see that I'm starting with a better result.
Now, let's move to the Screen Matte controls, I'm just going to take the clip whites somewhere around maybe 50 percent, I know that the dress has a couple of semi-transparent areas so it looks like we are in good state over here. I wanna, so you may want to clip the black just a touch so, always try to avoid moving those values for the clip black and clip white too much. Now, we can also use the rectangle mask just in order to crop this little problem that we have on top over here, and also remember to verify from the beginning to the end that nothing is being cropped when you are creating those masks.
Now, let's return to the final result for a moment just in order to check what we have so far, and you can press zero in order to preview the result. Now, here in this case, with the dress, it's up to you how far you want to take it. I'm sensing that they need to push the clip white, actually to reduce it just a touch in order to capture more of the dress and not just the transparent pixels that we saw, specially in this area, but this is of course up to you and it may differ from footage to footage.
Also note that I'm specifically using just one instance of Keylight, there will be cases that you will need to crop the upper part and the lower part and work on each one of them individually, but now let's move on. I'm going to press "cmd + '+'" a couple of times in order to move to 100 percent, this will allow me to get a closer view and to take a look at this key. The next step is usually to shrink the matte and to introduce some softness.
Values of negative one and one are usually acceptable for the shrink/grow, in this case we are shrinking the matte in one pixel and we are introducing a little bit of softness, once again just very low numbers in order not to harm the footage. And you can take a look at it in couple of places just to make sure that it is acceptable, you can also drag it just to make sure that we are seeing enough details in the hair, and I think that we are.
So let's bring it back to fit the view, and then let's choose a replacement method, this is more over personal preferences, I usually go with Hard Colour, although Soft Colour will give you a more contrast version, but I've found out that Hard Colour is actually a good start for most cases. Now, the replace color is actually what's going to be used in order to replace the green spill, so if you want to take a look at the intermediate result this is what we are actually getting just by keying out the couple over here, however the Keylight effect has a built-in suppress engine that will try its best in order to solve this and remove the green, and this is what we are seeing here whenever I'm choosing the final result.
Just know that you can change the replace color, it don't have to stick with the neutral gray, you can actually click on this picker and choose something from the background, in this case some light blue, which in this case helps to improve the footage and actually give us a better result. Now, the last thing that I'm going to do here, and I'm just going to close the Screen Matte, is introduce a little bit of Foreground Color Correction. So let's open it up, let's enable the Color Correction, and then I'm going to fold down the Color Balancing, and then I'm going to play with the Saturation and Hue values.
Now, note that in previous version you can actually open up this Color Balance Wheel and play with it graphically, but on my machine at least since Creative Cloud this Color Wheel graphic is not going to show up, doesn't really matter, we can still work with the Saturation and Hue values. Now, I'm just going to exaggerate it for a moment just so you can get a sense of what we are doing here, so let's plague in maybe 10 for the Saturation, and then let's just move the Hue until we find something which looks more or less similar to what we are seeing in the background.
Now, already we have a better match in terms of colors between our foreground key and our background, but usually I'm going to recommend to remove a little bit of Saturation in terms of Color Correcting if you don't want to overdo it, so a value between two and four is usually what I'm going to select over here. Now, just to show you this is before, a very neutralized version, and this is after, much better in terms of matching the foreground and background one to another.
Okay, we actually finished with Keylight but there is one more important step that you need to match, and unfortunately you cannot do it inside Keylight, and this is the amount of grain and noise. So for that I'm just going to press "cmd + '+'" a couple of times just so we will be able to match the noise between the foreground and the background. For that you can use this pull-down menu and choose from the channels, or hold down "opt" on the Mac, "alt" on the PC, and press one for the red channel, two for the green, and three for the blue.
In this case I think that we are in good state, but if you are seeing differences between your foreground and background go ahead and either add grain by using this effect, or you can actually try to remove the grain by using this effect. However they are very slow, so if you do need to add noise to your footage I highly recommend to use this guy, the Noise HLS Auto, and I'm just going to drag it over here and from the options I'm going to choose grain instead of uniform noise, and then usually I'm going to start with very low numbers for the lightness, so in this case let's go with two percent and then click away and then once again let's just test it by pressing "opt + 1", "opt + 2" and "opt + 3", on all the three channels.
Once again, this is something that you need to judge using your own experience and your own eyes. So let's fit back our Viewer, and actually let's test the result full screen by pressing "~" and make sure that you are rendering the preview in full resolution. So remember, the most important steps are to choose the right key color to begin with, and then work on the mat, and move to matching your colors and edge treatment if necessary.
You can achieve all of this using one instance of Keylight for most cases, then for better compositing remember to match the noise or grain. Of course not all shots will be the same and sometimes you'll need to crop and work on different parts of the shot separately, but these principles should apply as a starting point for most of your clips. The work on this shot is not done yet, we need to pay attention to the light direction, which in this case comes from the Sun behind the couple, so we need to create some kind of a light work to make it more believable, and I'll show you how to do this in the next movie.
- Compositing tricks
- Handling tricky keys
- Matching shutter phase
- Removing banding
- Matching color
- Adding an illusion of depth
- Watermarking shots