© 2014 by GATIMEDIA

GM_EDGE HUSSAR

The Problem

 

When you have a blue/green screen plate it is a quick way (and usually a smart too) to use Additive Keyer ( can be ScreenXchange or Soft Keyer or any other gizmo that basically does a similar job through a different process ). Regardless what you use to mix the BG with the FG to get the fine edge details every now and then you might notice that the BG colour contaminates the edges. These are usually not blue or green enough for the additive keyer to recognize as part of the BG so won`t get treated. 

Solution

 

One way to deal with this issue is using different despill methods that work sometimes. This current proposal to solve a problem operates on a more radical way and recommended to use on a denoised plate ( for now )therefore not always adviced to use, rather when the edges are damaged to a length that you can clearly see on the BG colours channel that something is missing or when you want to treat an annoying few pixels around the edges.

What the Edge Hussar does is separates the texture from the color first. Then it uses a common despill expression on the texture. Swapes the channel on the color. Then puts the two back again. And that`s the core thing.

Let`s see what you can do with this node and how to use it:

 

First, about the inputs:

- plate: This is where the image goes after you used the Additive Keyer on it.

- alpha: Connect to the matte you made for the plate. It's advised to be as accurate as possible for a better result. 

- mask: This one is for a garbage matte to select the area you want to treat. You can also switch off this option at `Mask / Mask Ignore` so the treatment affects all the edges around what comes in on the `alpha` input.

 

MAIN / Screen Type:

In order to use a right despill operation and swap the right channels first select the BG color.

 

MAIN / Multiply:

This is where you can adjust the color of the edges. As you will notice it affects all the pixels regardless if it is part of the BG or FG so make sure you select the right amount of pixels around the edges.

 

MAIN / Exposure:

Here you can adjust the brightness of the selected edge. 

 

EDGES

Here you can select the area you want to treat. It basically uses a `xor` operation on your `alpha` input so you can select more accurately the right amount of edge you want to treat.

 

MASK / Mask Ignore

Here you can turn off the `mask` input and use the treatment all around the edges of the `alpha` input.

 

MASK / Mix

Here you an adjust the overall mix level of the treated and the original edge. 

RANGES / Color by ranges

Here you can use the same `Multiply` operation but on the different ranges separately.

 

RANGES / Exposure by ranges

Here you can use the same `Exposure` operation but on the different ranges separately.

 

RANGES / Range Blur

Here you can adjust the blur between all three of the ranges.

RANGES / Ranges

If it seems like the selection of a certain range should be modified here you can do that using luma keyers.

Here's an example of how using a node should effect your comp:

Let's zoom in to the left side of the bison to see the difference better:

Also a very simple script just to show the recommended place of the node in your script.

Hope you will find it useful! 

Here's the GitHub link ( just select the text and copy to Nuke )

example image is from Escape Studios©