Timeline FX: Axis -- Keying

Uploaded by SmokeHowTos on 11.06.2012

In the previous video, you looked at how to do basic tracking and stabilisation in the Axis Timeline FX.
The last function we will cover in the Axis effect is the keying tools.
In an earlier video, I inserted a background plate of the coliseum on track 1 of the sequence.
I have already added the corresponding green screen source media onto track 2. I have also added an Axis Timeline FX to the segment
so we can start keying straight away.
Let’s go into the Axis editor and in the center of the controls, you will see the Keyer button.
This is your first entry point into the keyer.
Inside the keyer, you have 7 chroma keyers to choose from.
Each composite has it’s own unique set of problems to the solve, and several ways to solve them,
hence the multiple ways to key an image.
The default keyer that is applied to the image is a luminance keyer, hence the result in the viewer.
For this example, you will be using the Master Keyer at the top of the list.
The first step in the workflow is to remove the key colour.
Click on the left grey colour pot and the cursor will turn into a colour picker.
Using the master keyer, click and drag across the green in the viewer.
When you release the cursor, the master keyer samples an average of the green colour and applies the appropriate key.
The result looks pretty good but in order to make it perfect, you need to see the alpha or matte channel
generated by the master keyer.
To the bottom left of the screen is the viewer pull-down menu.
Click the button and change the view from result to matte.
Black is transparent, grey is semi-transparent and white is opaque.
You can see there are issues in the tunnel part of the shot
and you can fix this in three ways.
Firstly, you could click anywhere on the image and the on-screen sliders will allow you to adjust
the different luminance levels in the alpha.
Secondly, you could adjust the histogram and Matte controls to adjust the black and white colours in the alpha.
This is good in some instances but it could get rid of good detail.
Finally, the method we will use is patching.
This method allows you to work in isolated areas of the key.
Under the sampling title, you can change the pull-down menu to patch 1.
Hold down the on-screen keyboard shortcut and drag a box over the area you want to repair.
Notice how Smoke picks up the right colour in order to add or remove areas from the matte.
You can keep dragging boxes over the regions until the areas are fixed.
You can also tweak the sensitivity of these patches in the sliders below.
I’ll just use a second patch and sample the black areas to ensure they are 100% transparent.
Let’s switch the viewer back to the result view to see the result so far.
So the alpha channel is looking really good right now, but the colours have gone a bit strange.
This is because the keyer uses Automatic colour suppression by default.
This is often called spill suppression in other keyers.
You can adjust the range slider, if too much of the key colour has been suppressed.
In addition to suppression, you can also colour correct your keyed image from within the keyer.
Click CCF to enter into the familiar colour corrector.
I’ll quickly switch to the colour warper, and use the colour matching technique that
I showed you in the video about colour correction in the sequence.
Once that is complete, I’ll press return to exit the colour warper back to the keyer.
One other area you need to work on when doing keys, is the edge blending.
Keys usually land up with dark or bright edges and they need to be balanced,
to correctly blend in with their backgrounds.
By dragging the Luma slider, you can see of the edge brightness adjusts and you can match it
so that the key sits better in the background.
One final task in keying is roto-scoping.
Let’s say that I want to remove this pillar to the right of the gladiator.
I can’t key it because it is not green but I can mask it out.
Switch to the Matte view through the pull-down menu.
In the keyer, you can switch to the Gmask menu.
Gmask is short for garbage mask, for masking out areas of your image.
You might call this a mask in other applications.
To create a gmask, click on the add button. You can now click and drag a shape around the pillar.
To complete the shape, you can either click on the first control point or click the close button
and Smoke will complete the shape for you.
Once the shape is closed, it is filled with a white colour.
Click on the colour slider and change the value to 0 to make the masked selection transparent instead of opaque.
To feather the edges of the mask, drag the off-set slider
and if you want more refine edges, you can switch to the advanced edge gradients
and adjust the feather on a control point basis.
Scrubbing the time-bar, you'll notice that the shot does move slightly.
So I’ll turn Auto-key on and I can animate the mask.
You can animate the control points of the mask, individually, in a group, or the whole shape.
I’d like to mention to you that you could use the Stabilizer tool to track individual points if you wish, or the overall shape.
Switching back to the Result view you will notice the keyed result with the applied mask.
You can press the return button to exit the keyer and the exit button in the axis timeline FX to return back to the sequence.
You can scrub the segment to preview the result or press the render button to render the final output.
In the next video, we go beyond timeline based compositing and start exploring the ConnectFX procedural node-based compositor.