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How can I trigger an effect when the color change at a certain area.

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Aljoscha Oltzen
How can I trigger an effect when the color change at a certain area.
on Aug 3, 2018 at 7:39:04 pm

Hello Guys,

how can I trigger an effect based on the color in a certain area? To make my question clear you can imagine a video file with hundreds of white areas. Over time some of them turn red and then turn white again at random. And I want to put some effects (a particle, some lightning effects) on theses areas when they are red. So the effects should start when the square turns red and stop when it turns back to white.

I know this is a tricky question, but there should be a solution. Maybe an expression is the key. Sadly I don't have much experience with expressions.

I'm thankful for every contribution.


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Michael Szalapski
Re: How can I trigger an effect when the color change at a certain area.
on Aug 3, 2018 at 8:08:42 pm

I would use keying techniques to pull out just the red areas and then use that layer to drive your effects. Without knowing in a bit more detail what you're doing, it's hard to say.

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Steve Bentley
Re: How can I trigger an effect when the color change at a certain area.
on Aug 3, 2018 at 8:59:15 pm

Instead of keying you can also use the set channel effect to send a channel that won't have any red in it (then invert it) to be used by your particle engine. You might think, "I'll use the red channel" but the white squares will also show up in that channel as white is one third red. But the red squares won't show up in the blue or green channels, so use one of those and invert it - that will give you a black and white element where the red squares are white and you can use that to drive you particle emission.



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Aljoscha Oltzen
Re: How can I trigger an effect when the color change at a certain area.
on Aug 5, 2018 at 5:22:25 pm

To be more specific, I want to make an effect in a video similar to this one:







I want to find out, how they trigger these particle effects, everytime a key is played. To use keying techniques for this, seems a bit unpractial.


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Steve Bentley
Re: How can I trigger an effect when the color change at a certain area.
on Aug 5, 2018 at 9:10:21 pm

It's not so much the particle effect that's triggering the keys, it's the musical notation triggering the particles. There's software for this but you can do it in ae. More later.



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Steve Bentley
Re: How can I trigger an effect when the color change at a certain area.
on Aug 6, 2018 at 6:14:04 pm

In the new AE you can now access data files to generate graphics. Whether you have a midi file or a text based notation of your music will change the pipeline here but both of these are convert-able to something that AE can understand.
I'm not sure a particle system would be the best though. It might be better to (if you want to do this sort of thing in AE at all) to write a script that has Classes. A master note Class and then inherited classes for whole notes, quarter notes, sixteenths etc. As AE steps through the data file, it would generate the correct solid for whatever kind of note it finds and that solid can be told to descend the screen at a constant rate. You can use position and size parameters in Expressions to trigger which key lights up in the bottom graphic.

You can also do this all manually of course but depening on length of song that could become a life sentence.

If it doesn't actually have to match a piece of music and its just something like your example, and you still want to use particles, you can have a Particular emit a random shape (from a precomp of a group of specific shapes) and have a collider mask down where the keyboard is. When the particle hit that mask they will generate another particle that "lights" up that key.



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Aljoscha Oltzen
Re: How can I trigger an effect when the color change at a certain area.
on Aug 8, 2018 at 6:37:36 pm

Thank you for your post.

I do have a midi. And I don't want to recreate Synthesia. I will capture Synthesia footage like everyone else. I only want to "recreate" (of course in my own way) this particle effect you can see in my example video. That's why I don't need to light up the keys. They are already lit up by the program. I only want to add this particle effect in my Synthesia footage.

So what are the possibilities to import a midi into after effects? I've only read something about an unofficial script which can import midi into after effects. But this script doesn't work with my AE version (CC 2018). So is there another way?

Best,

Aljoscha


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Steve Bentley
Re: How can I trigger an effect when the color change at a certain area.
on Aug 8, 2018 at 6:54:13 pm

Oh I see what you are talking about - the little particles at the top of the keys. Ok, that's pretty easy. Make a mask that essentially makes a line just at the top of the keys. Then pass the footage of your descending "notes" through that mask. Precomp that.
Use that precomp layer for Particular to drive the emission of the particles. The particles will only emit when a note passes through that region and only while the note is passing, and in the area where the note crosses that line mask.
If you want you can also have particular take the color of the note that's passing and use that as the color for the particles.
From the looks of the particles, you will probably need to turn on auxiliary particles so that the first batch of larger particles emit secondary particles. You could also use two or three copies of your layer with Particular on it and have a different style of particles for each layer

Comp all the particle layers on top of the original footage.



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Aljoscha Oltzen
Re: How can I trigger an effect when the color change at a certain area.
on Aug 9, 2018 at 10:24:35 pm

Thank you Steve,

Your answer really helped and it worked quite well. I have now achieved the effect I've envisioned. Thank you very much!


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Steve Bentley
Re: How can I trigger an effect when the color change at a certain area.
on Aug 9, 2018 at 10:33:10 pm

Sorry that took so many posts - an ad popped up on top of the video, covering the tops of the keys, so I didn't see the little "popcorn" particles until the second viewing. I thought you meant just the falling "notes".
Glad its working out.



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