VFX – Paint Mattes & Chroma Keying

After Effects can sometimes be a little troublesome when looking for the solution to a new problem due to how deep and almost hidden its menus can be. Hence the first exercise in this class was looking at a task another student had asked Peter, which stumbled into some road blocks while looking for the correct tools. We would create a reveal using the paint brush tool, a quick and simple exercise but not so obvious.

Paint Matte

We began by importing a new image from the selection that Peter had provided from his own renders. The composition was set to use the dimensions of the image. As usual I’ll run through the rest in bullet point form.

  • New solid, black, comp size
  • Select the Brush tool
  • Double click on the new solid
  • Set brush colour to white
  • In Brushes panel (right hand side) set brush dynamics to pen pressure OFF
  • Change brush size to something large (600) – Draw over the solid in your own pattern


  • On the timeline, drop down the black solid layer, effects > paint > Brush1 > Stroke Options > Key ‘End’ to 0% at the start of timeline, key back to 100% where you want the reveal to end.
  • Change the Track Matte of the image layer to Luma and scrub through the timeline. The final result is below.


Chroma Keying

Now onto the main exercise of the day. We would be taking our first look at chroma keying or in the common tongue ‘green screening’.

We were given several layers of footage. A 3D rendered camera pan in a lobby, a depth of field render for the same scene and green screen footage of a woman shooting a gun where the camera pan matched the 3D render.


This was a long process, so here goes.

  • First, drag the pool footage into the composition twice, then bring in the depth of field footage as the top layer.
  • Change the middle layer’s track matte to Luma Matte.
  • Add a Gaussian Blur and curves colour correction effects. The colour correction was to darken down the background. Together with the depth of field footage this would make the rendered scene less crisp and a little more realistic.
  • Pre-compose these layers into one and name it “Backplate”.
  • In the new composition, drag the chroma key footage in as the top layer (above backplate) and change the opacity to 50%.
  • Pre-compose again and name this one ‘Quick Reference’.
  • Create a new composition called Key and drag in the ‘backplate’ and the chroma footage as the top layer.
  • Using the After Effects plug-in Keylight (a rather brilliant bit of kit that will auto remove the colour from your chroma footage), select a green close to the body using the eyedropper. Making sure you’re on frame 1. The green in the chroma footage will immediately vanish, ALL OF IT! While keylight does its best, some traces of green may remain, especially in reflective surfaces, skin tones etc.


Looking good but still requires a lot of cleanup.
  • Time to play with some settings. Change view from Final Result to Screen Matte.
  • Under Screen Matte options, change the black and white percentages to Clip Black 25 and Clip White 68.
  • While still under options change Shrink/Grow to -0.5 and Screen Softness to 1.
  • Under Edge Colour Correction we changed brightness to -9.
  • Add a curves adjustment to the chroma footage to adjust the actresses black levels to closer match the scene.
  • Pre-comp the scene again and this time we called it PREGARBAGE.
  • In a new composition we stacked backplate and PREGARBAGE.

From here on it was a case of masking out all the parts of the chroma footage we didn’t want using the pen tool, making another duplicate of Backplate and PREGARBAGE if we wished to repeat the process on a new section of footage.

In trying to be smart and thinking I could remove everything with two masks I ended up with a lot of mess around the gun, animating the mask to try and move with the gun frame by frame wasn’t a great way to go about the exercise. Instead I’ll leave you with Peter’s unfinished attempt.


This exercise has been a real eye opener to how delicate and time consuming a process this kind of work is, I can see a perfect end result being very rewarding. I’m hoping we get to continue learning more of the process, tips and tricks for clean up etc. Keylight seems like an amazingly helpful bit of kit.

As mentioned in my update on Skuldworks, Peter is leaving us and this was his last exercise. As of next week his replacement Gary will be continuing our journey through VFX.



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