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Green Screen and Ultra key

An article to go with the green screen ultra key Premiere CC tutorial

Equipment

I don’t have a studio, I don’t even have access to studio facilities, all I have is my “den” which is a room 2.5m x 6m in size. This doubles as my “studio” and my “editing suite”

Lets go through my equipment that I use.

This is my Mic which I have on a boom arm

This is my camera

Yes it’s a cellphone and why not. The cameras on a modern cellphone are fantastic and are very close to to DSLR standards, this happens to be my old “out of contract” phone that has been repurposed for making videos.

I use NDI over ethernet to bring the images into my computer with this adaptor

For my green screen background I have a portable blind.

For lighting I use these for sidelights

And the front key light is this

The software I use to record the initial green screen clips is OBS and then I import the recordings into Adobe Premiere for the Chroma keying.

Chroma key

One of the most important things I discovered early on was the importance of even and bright lighting on your background, it doesn’t have to be perfect but if you can eliminate as many contrasting areas of dark and light as you can it makes the whole process so much easier

Lighting


This is about the best I can do with my setup, it’s not perfect and I still have a fairly dark area bottom left but because there are no harsh lighting changes throughout the background it makes the whole process of keying much, much easier.

Once the green screen segment is recorded and I am happy with it I then import it into Premier.

How to Chroma key

Have your effects window open, if it’s not visible just go to the top menu window then select effects so that it’s ticked

Effects

Next go to the effects tab and type in “Ultra” this should find and show you the Ultra key effect.

Ultra key

Grab and drag the ultra key effect onto the clip and then go to the effects control window, if this isn’t visible just like making the effects window visible go to the top menu select window then select effect controls to make sure it’s ticked.

Effect Control

Go to your effect controls window and look for Ultra key, you may have to scroll down to find it.

Ultra key effect

Different people do the next step in different ways what I do is go to the setting box and select “aggressive” and I use this as a starting point and fine tune it a bit later.

Next select the eye dropper next to “key colour and go to your clip, I always pick a point close to the hairline and then click the dropper and the magic happens, Premier will remove all the pixels that are the same colour as the pixel under the dropper.

Removed pixels

In this case it’s done a pretty good job of removing everything green and leaving a fairly solid black background, except here on the bottom left it’s a little grey which means that will notice on the final render, there are several ways to deal with this, the first is the simplest, just go back to the eye dropper tool, click it and your green will be restored and then click it on a different part of your clip and do this several times until you can get the most even all over black you can get but don’t worry if you can’t get it all over, this is just the shotgun approach to removing the pixels, now we go in for the fine tuning.

What I do next is to select the alpha channel

Alpha Channel

It always surprises me how it shows up that the background removal isn’t as even i thought when I watching the composite view. Again I just reselect areas with the eyedropper or I just select aggressive again which normally gets me the best result.

Pedestal

Once I am happy I then open Matte generation and go to the Pedestal control, this is the single most important chroma key control, I increase it in very small steps until I get as even a background as possible but without losing any of the white area, if you start to see black creeping into any of the white area you have gone too far with this control and need to back it off a bit.

Contrast

Next I will go to matte cleanup and the contrast control and once again slowly increase it until you get an even black but not losing any of the white detail, all the time I am constantly changing between composite and alpha channels to check what I am doing and if I have gone too far with a control.

Choke

I am now happy with the background and am going to really fine tune the key, I notice on my left arm I have some green fringing along the edge of it so I am going to use the choke control to remove that, in this case less really is more, small tiny increments until it goes without affecting other parts of the image

Spill

The last thing I adjust is the spill control, the green colour of the blind is reflecting on my face so I am going to use the spill control to remove that, I slowly increase it until the green goes as best as I can without affecting any other part of the image, sometimes I might have to balance this by altering the choke a bit either way to stop the fringing from appearing again.

At this point if I can either bring in a back ground image, a background movie or just export it as a clip with the background removed so I can superimpose it on another clip in another project.

The clip we have just chroma keyed is the Top layer so any imagine or clip we bring in has to go underneath our clip on the timeline so I might have to move the keyed clip up, if I am happy I then export it as an HVEC.

I normally just export it with no background at all so I can import it into another clip at a later date.

IMPORTANT

If you are going to do this then you MUST export your clip as a quicktime movie with alpha and not an HVEC or H264 .mp4 file

Export as a quicktime movie

To do this in the encoder just select Quicktime as your format then any of the presets that are “with alpha” I normally use ProRes 4444 with alpha or GoPro Cineform with alpha.

I hope you enjoyed this tutorial and I hope it helped you.

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