Combining a video and a masking video

Question

We have recieved 2 video files:

1. the video with the main character dancing in the middle
2. an identical file in terms of the animation but the main character is in red, whilst everything else is black.

I imagine the latter is some kind of a mask.

What we would like to do is combine them, so you can only see the bits in file #1 that overlap the red bits, whilst ignore all the black?!?! eg. Just the dancing character that we can choose a different background.

It's like the hard bits been done, we just need to combine them. We have the full adobe suite, but if someone could point us in the right direction?

We had a play, and added both assets in Premier, and as an example set the #2 file to multiply blend mode... It's the effect we want, but obviously the main character has a red overlay.

Any ideas would be much appreciated.

Thanks

Answer 1

Method 1

1. In your timeline, stack the matte clip on top of the character clip and add the Ultra Key effect to the matte with the red color as the key.
2. Nest those two clips, and place another Ultra Key effect on the nest, this time keying the black.

You'll probably have to mess with the ultra key settings a bit (transparency, choke, and soften) for both applications, but after you've got that set you should have a masked clip ready to place on a new background.

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Method 2

There's also a way to do this with the Track Matte Key effect that yields slightly different results, you can decide which method works best for your matte.

1. In your timeline, stack the matte clip on track 3, the character clip on track 2, and your new background on track 1.

   

2. Add the Luma Key effect to the matte.

3. Add the Track Matte Key effect to the character clip with the Matte set to Video 3 and Composite Using set to Matte Alpha
4. Adjust the Threshold in the Luma Key effect in the matte clip if the keyed content is transparent, or adjust the Cutoff if you can still see the black.

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I find that the first method gives more control over how the final key looks, but Ultra Key is a complicated tool and the second method is a little more straightforward.

Answer 2

In Premiere

To avoid the trip to AE you can do it in Premiere, but it does increase the complexity of your timeline. You use the Track Matte Key effect, plus a colour key effect. It's a little tricky, but here's the basic set-up:

• start with your three layers. On the bottom, the background that the dancing man is going to be in front of. Could be empty if you just want the infinite blackness of the Void. Above that, the dancing man, and above him the red/black matte layer.
• select the red/black matte layer and apply the Colour Key effect (there seems to be a bug where it's spelled Color, but Adobe refuses to do anything about it). Use the eye-dropper to select the red colour of your matte. No, actually select the black of the outline. If you turn off the video 2 visibility at this point you should see a red man dancing in front of the bg.

• select the dancing man clip and apply the Track Matte Key. Set the Matte source to Video 3, the layer with the red/black matte. Nothing will happen yet, patient you must be.

• the Track Matte key applies the alpha of one layer to another layer, but it uses the alpha of the layer before any effects are applied. To force it to use the alpha created by the colour key you have to nest the layer with the colour key effect. Right click the red/black matte clip and choose Nest…. This will create a sequence with just the red/black matte in it and replace the original clip with that sequence.

At this point with all the layers visible you should see you dancing man over the background layer.

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In After Effects

Another way is to put do step 1 above, and then select all the clips and choose Replace with After Effects Composition. This will create an After Effects project with the 3 clips in it. In After effects you would create the composite thus:

• on the second layer (dancing man) you need to set a track matte. In the modes/switches panel (if it's not visible hit f4) set the Track Matte to Alpha Matte

• now you need to create the transparency for the top layer. If the layer is CGI using the Set Channels effect to use the red for the alpha. Set Source Layer 4 in the effect controls to the top layer; the red/green matte, and set Set Alpha to Source 4's to Red

• since we're using the red as the alpha, we'll actually have to reverse the matte. On the second layer, change the track matte to Alpha Inverted and now you should have a dancing man over the background.

You could also use any of AE's multiple colour key effects to create the transparency if the Set Channels effect doesn't wotk. To name a few, there is a simple Colour Key effect, a Colour Range, a Linear Colour Key and Keylight, in rough order of complexity.