VFX – Brush Reveal and Keying

We started off class today by looking at a task another student had asked Peter about: how to do an image reveal using a paint brush. This actually works quite easily, given the knowledge that we’ve learned over the last few months.

First, we had to open up the image we picked from the array Peter provided. I chose one that looked quite sci-fi to me, which was called Large Hadron Collider. We then had to add a black solid to the composition and double-click on it to go to its specific layer.

From there and using the brush tool, I changed the colour to white and chose a larger sized brush. The one thing we had to be sure of was that, in the brush dynamics, the “pen pressure” had to be turned off. We could then painting across the canvas in whatever fashion we wanted the reveal to happen – I just chose to go from the top-right corner to the bottom-left, which was as Peter did in his example.

After that I could close the layer and go back to the composition, where there was now an effect under the black solid:


By changing the end time to 0% at the beginning of the timeline, keying it, then going to the end of the timeline and changing it to 100% before keying it, there was only one more step to go before the desired result was achieved. It was merely a matter of changing the track mat of the picture to a Luma Matte and playing it through. Below was the final result and I think it looks really good for the few simple steps it takes!


After that, we moved on to keying (chroma key compositing), which is used for taking green/blue screen footage and compositing it with another layer into one piece of footage.

We were going to take some footage of a woman shooting (below on the right) and combine it with a sweep-through a lobby-like location (below on the left). We were also provided with a depth of field version of the backplate (below in the middle).

First we had to drag the pool footage into the composition twice, then bring in the depth of field footage as the top layer. After that, we needed to change the middle layer’s track matte to the Luma Matte option, then add a Gaussian Blur and curves colour correction effects. This would make the footage seem less static and more realistic.

Having learned about pre-composing last week, we would pre-compose these layers into one and name it “Backplate”. This will be the main background footage that will take the place of the green screen. In this new composition, I needed to drag the chroma key footage in as the top layer and change the opacity to 50%. This would then be pre-composed into another composition and named “Quick Reference”.

In a different composition, which we named “Key”, we added in the backplate composition and dragged in the chroma footage as the top layer. This is where we got to explore a different add-on in After Effects: Keylight.


This is a piece of software that comes with After Effects which will look for the screen colour of your chroma footage and essentially replace it automatically for you.

In the past, this was done manually with masks and a lot of talent, however this Keylight software makes the entire endeavour so much easier.

From the colour picker next to the Screen Colour, I chose a colour of green that was near to the actress in the chroma key footage. Sometimes the problem with the chroma footage is that there are a variety of greens throughout – the green could wash out the people, make them look sickly, or reflect off of various other items in the scene (for example, the shiny coat our own actress is wearing).

Keylight picks up on the hues of the colour you choose and lifts them from the scene, making sure it all looks more realistic, which is the entire point!


The result looks better already, but it’s still not nearly done!

In the Keylight’s options further down, under the Screen Matte menu, we changed the clip black and clip white percentages to soften the edges. We also changed the screen shrink/grown to -0.5 and the softness to 1. Finally, the last thing to change in the Keylight effect was enabling the Edge Colour Correction and change the brightness to about -9 (or whatever felt right to us that matched the scene). Adding a Curves Colour Adjustment to the chroma key footage would also help with making her appear less dark in the otherwise lighter scene.

My file seems to crash my computer, which is a bit infuriating since I would have liked to finish the cleanup of the footage. We were shown how to mask out the garbage by using multiple layers and the pen tool to draw around the various parts of scenery we didn’t want to include in the final footage.

I’d spent a lot of time trying to mask around the gun to avoid the clipping issue and I’m about half-way through; I think I’ll continue if/when I have time in college, since the computers there seem to be able to handle the huge footage file sizes better than my very full computer at home! However, below is very similar rendered footage that Peter provided for us.


I think the entire project was really interesting to learn about and will help me make an excellent contribution to my final portfolio presentation at the end of the first year! These sorts of effects seem rather straight-forward in principle, but take a lot of patience and a keen eye to make it look really good. I’m looking forward to trying this out for myself at some point in the near future!

Posted in VFX

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