Vision Mixer Green Screen

You should have become familiar with the contents of Vision Mixing Guide ‘Basics’ before tackling this presentation

‘Basics’ looks at the techniques of cutting between vision sources - cameras, video titles etc - how to select wipe patterns and adjusting the duration of transitions.

In this section we are going to cover:

Creating the Chroma Key in the Vision Mixer
Selecting the 'Fill' Signal
Selecting the 'Key' Signal
Defining the 'Key'

A staple of film and television production - Chromakey means you can shoot a subject against a green background, and replace the green areas of the image with any still or moving image you like. This effect can also be created in an edit. Sometimes blue is used instead of green.

Creating Chromakey in the Vision Mixer

It can be useful to set up chromakey effects on the ME1 bank of the Vision Mixer - outlined in red. ME stands for ‘Mix Effects’. This means you can do normal cuts etc on the P/P bank and use one button - ME1 OUT - to bring up the Chromakey effect when needed.

NOTE Using Chromakey for lower thirds is dealt with in a separate presentation.

To make sure we are monitoring the ME bank, put it ‘On Air’ by pressing the ME1 OUT button on the PROGRAMME row of the P/P bank of the mixer.

Selecting the 'Fill' Signal

It could be a still or video. Let’s say your background is coming from GFX1….put GFX1 on the output of the ME bank of the mixer using the upper row of coloured buttons.

This is the Programme row of the ME bank. ME stands for ‘Mix Effects’.

Selecting the 'Key' Signal

Now we have to tell the Vision Mixer which source is being used to produce the ‘key signal’ - which it uses to create the effect.

If CAM 1 has the shot of someone standing against green we use the Destination & Source buttons on the ME bank (the smaller, white buttons) to put CAM 1 into ‘KEY 1’.

We switch KEYs on and off in the KEYER module at the right of the ME bank….
CAM1 is in the window below KEY1 because we selected it in the previous step.
Turn KEY1 on using the button above the window - the button will turn red.
You will not see the Key Effect yet.

NOTE

Once set up, you can switch the Key on or off using the same button, or use KEY1 TRANS to mix or wipe the Key on/off.

Defining the Key

We now need to define* the KEY using the ‘FLEXIPAD’ at the top of the mixer panel. The function for setting up a Chromakey is semi-automatic.

*NOTE

This is because there are others types of Key apart from Chromakey and we need to select the right one.

Using the white buttons at the left of the FLEXIPAD….

Press KEY ADJ* and then M/E 1.

The buttons light up to show they are selected.

*Key Adjustments

The buttons on the right change to offer KEY functions…

Select KEY 1 on the top row.

On the second row select CRK for Chromakey.

Press SMPL MARK (sample mark).

You should see the CAM 1 shot with a white square.

This is the SAMPLE MARK. We use it to sample the exact colour of our green screen so the mixer can create the Chromakey effect.

NOTE

You can use different colours to create a Chromakey so the sample mark tells the Vision Mixer which you are using. (Green or blue are usually used as there is very little green or blue in human skin tones.)

Use the black knobs to the right of the FLEXIPAD to adjust the position and size of the square.

SONY says you should make it as big as possible but keeping it on the green part of the picture.

Press AUTO START.

After a few seconds you should see your composite picture.

Your composite shot:

Notice the red halos on the monitor stack showing that CAM1, GFX1 and ME1 OUT are all ‘on air’.

Note too, the red buttons on the mixer surface, showing the elements ‘on air’, including KEY1 on the ME bank.

Good lighting is important - e.g. an evenly lit cloth & good background/foreground separation.
The key is LIVE….. you can change the background to anything on the ME1 PROGRAMME row of the mixer and changing the camera shot will move the subject relative to the background, making the shot more or less realistic.
If the KEY is not perfect you can adjust settings via the touch screen (ask for TD help).
Creating a natural look - e.g. for a drama - is trickier than something more obviously staged.
There are limits…. talk to the studio team about a project using Chromakey extensively.

Written by PS

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