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When you're shooting footage next to a gigantic green wall, it's not unusual to have some of that green unintentionally fall on your subject. . In this segment we show you how to remove the green
using keylight, spill suppressor, and curves in after effects, as well as ultra key and the 3 way color corrector in premiere pro.
Using the right combination of these tools can restore the natural look to your green screen footage.
Removing Unwanted green, also known as spill, from your subject is a common issue that editors face when working with green screen footage. We'll discuss 5 different approaches to solve this problem,starting with keylight in after effects.
The Bias controls in keylight are used to help color-correct the foreground. Locking the Bias controls together is typically the best way to get the results you're looking for. In this case, we'll use the eye dropper and select the skin tone from the foreground actor. Viewers are much more likely to notice skin tones that aren't quite right. If it doesn't look right, try a couple of different points until you get the desired result. Now this seems great, but one common issue with this method is that your footage can become very grainy. In this shot, the technique works with minimal grain (07), but in this alternate shot, the grain was far too intense to be useable (11)
When you modify your screen matte controls to pull your key, keylight has a method to intelligently blend the pixels that are similar to the screen color.
You can change how keylight handles these pixels by changing the replace method. Switching our view to status will help you see some of the pixels that keylight is applying this correction to. The green areas in this view are being modified. In keylight 1.2, the default is set to soft color, with a grey tone. Let's switch this to hard color, and change the replacement color to red to see how this works. Basically, when you increase the alpha channel, the hard color method adds the corresponding amount of the replace color you select back into your image. By adjusting the clip white, you can see that the intensity of the red replacement is increased.
Now let's switch to the soft color replace method. This method also adds the corresponding amount of the replace color you select back into your image, but keylight modulates the luminance of the pixel to try and match the original, giving a more subtle result. Switching our color replacement back to grey will show you a more typical result. Depending on your situation, both these methods can be effective.
Changing the color replace method to source will simply have the original pixel added or removed when the alpha is altered, while selecting none will disable the feature completely.
Another approach to reducing the green in your foreground is to use the spill suppressor effect within after effects.
You can find the spill suppressor in the effects, keying menu. If we change our replace method in keylight to source, and then use the "color to suppress" eyedropper in the spill suppressor effect, we can select the screen color to match our keylight setting. We can then increase the suppression amount, being careful not to introduce any new color issues.
If your shot has an overall green cast to it, you can always use the curves effect to help restore a more natural color.
You can find this in the effect, color correction menu. After applying the effect, change the channel dropdown box to green, then adjust the curves as nessesary to remove the color cast from your shot. A little goes a long way, so don't over-do it.
Now let's take a look at getting rid of that green spill using premiere pro cs5.
In this example we've used ultra key to get rid of our background, but you can see we're left with some green tinge in our footage. There are four parameters under Spill Suppression we can work with. Ultra key automatically sets default values that you can adjust.
The desaturate parameter takes the pixels that are close to being fully transparent and desaturates them. The Range parameter controls the amount of spill that gets corrected. In this case I'm going to start by turning this way up. You can see this is introducing some red to counteract the green tint.
The spill parameter adjusts the amount of spill compensation. Essentially, how strong do you want the offsetting color to be. Lowering the value will reduce the intensity, and raising it will increase the intensity. In this case we'll lower it a bit, then make small adjustments to each parameter until we've got a nice balance.
The luma parameter works with the alpha channel to restore some of the original luminance of the source if necessary.
If your shot has on overall green cast to it, you can use the 3-way color corrector to address the issue.
This effect is in the video effects, color correction folder. Let's apply the effect to our clip. Using the color wheel interface will allow you to bring some flesh tones back into the shot using the shadow... midtone... and highlight parameters to get a great balance. Toggling the effect on and off can really show you the improvements.
There are so many variables when it comes to green screen footage that you're likely to need a host of tools to get it right. Using these different methods can surely help you on your way. In our next segment, we discuss what to do when your subject doesn't seem to fit into your background. This is an essential skill to making your green screen footage look more professional.