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Light Painting - show only cross sections of 3D objects for advanced light painting effects

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Roman Holtwick
Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 21, 2018 at 11:37:02 am

Hello folks!
This is my first post on this account, my old one was inaccessible and had a lot of outdated information in it too, so.... just for the record!

On topic:
For a bigger conceptual photo project involving light painting along with the neon look, I recently took a look at the app "Holographium". It allows you to type text and symbols which are then extruded and shown as cross sections over time, so you can paint these awesome holographic texts:





Since the app isn't updated anymore, nor are there any working similar apps (I'm on ios, assistants often have android, i searched both, nothing seems to work) I thought about how to recreate this myself. This would even give me a lot more control and possibilities!

I thought about creating some 3D stuff in AE (which I'm familiar with for special effects in live action and some animation for LED screens) and putting the rendered video on my smart phone or tablet. That would be perfect!

But how do I achieve this?
I positioned the camera in a 90° angle and flew through the extruded text I made as an example.This does NOT show cross sections (of course). I assume there is a very simple way to do this, something from the effects panel or so should be able to do the trick, right?

Thanks in advence everyone!


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Dave LaRonde
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 21, 2018 at 9:19:07 pm

I don't see anything in that example that must absolutely be 3D.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Roman Holtwick
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 21, 2018 at 10:33:31 pm

Can you elaborate on that? Of course you COULD do all this by hand but this would be a lot of trial and error and not really productive...

In case the first video was misleading here is an example of how the app was used back when it still worked:







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Dave LaRonde
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 21, 2018 at 11:01:04 pm
Last Edited By Dave LaRonde on Jun 21, 2018 at 11:03:07 pm

You're going to need a 3D application to replicate something like that.
Now, you COULD do it in AE, but I doubt spending many tens of hours tearing your hair out sounds like an enjoyable prospect to you.

It could be more than many tens of hours of AE work.....

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Roman Holtwick
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 23, 2018 at 6:09:31 pm

Well this is why I asked for some expertise...
However replicating this in CGI would be really easy, I'd still love to do it as a practical effect.
I think I will do it by hand...


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Steve Bentley
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 25, 2018 at 6:43:22 pm

Let me see if I get the jist. Am I right in assuming when you waved your phone through the air the motion sensor "deposited" a cross section of text in the air at the right time, leaving in the eye's persistence of vision or a camera's slow shutter a ghostly imprint of the whole word? Like those light sticks or LED bicycle spokes?
If you want to do that real time, then AE is not the program for you. Even if you made a movie of the effect I don't think a phone or tablet would play it fast enough and rip through enough frames to place the effect in the air with enough temporal resolution. Plus you have to time the doling out of frames to the speed of the phone's motion. It's hard enough to maintain a steady frame rate on a phone when what's really needed is a constantly and hyper accurate changing frame rate tied to the motion sensor chip. A custom video player would be needed or an app that generates and displays it on the fly like the app you mention.
But if you want to simply recreate the photos with text imagery over top, yes it can be done in AE but might be easier in a 3D package like C4d (and then into AE for the comp).
The key is the shader used on the text. You want something that has transparency, probably an edge hilighter (like a fresnel), and you may find that text built in 3d might be better constructed as a shell with thickness as opposed to a solid. A shell version will give more character (pun intended) to the letter's edges.
Then simply composite the result with a screen blend function on to your background image - light in the real world adds up over what's behind it and "screen" does this beautifully (ironically "add" can build up too much).
In AE zaxwerks or Element 3D could get you there for the 3D text (and there are a few others). You can also do 3D objects in Pshop if still are all your are after.



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Roman Holtwick
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 26, 2018 at 1:31:00 am

Thanks for giving a rel answer! You are (in parts) getting me right.
Let me elaborate (beacause I think it is actually A LOT easier than it seems):

Yes I am going for stills with this projekt, it‘s going to be long time exposures of 10+ seconds with a lot of different light painting techniques.

Neither I nor the app did bind the shown cross section to the motion sensor.
The app creates a video with a set length, say 10 seconds, in which it goes through all the cross sections of the text or object you like to generate.
This means you have to set your DSLR on a tripod and expose the picture for at least 10 seconds in which you habe to move the phone through the picture where you want the text or object to appear.
If you move it too slow the text will appear shorter, if you move it too fast it will appear longer.
I have tested this manually by making a circle in AE slowly growing bigger and then shrinking back to a dot, and putting the Render on my phone as a video (5sec.) and dragging it through a long exposure of 7 seconds to have enough time to start it and move it.
It resulted in pretty good spheres.
Now since I could do all of this in CG or Photoshop easily in said blending modes I want to do it as a practical effect for demonstration/education purposes, even if that means doing more complex stuff by hand.

But I would love to reverse engineer the sphere-example from above in such a way that I could load a sphere in AE and get it to render out cross sections of said sphere in such a way that it becomes a growing and shrinking circle. I could then use the same method on more complex objects like text, a car a skull or whatever...

In other words, forget all the above and tell me the simplest way to get AE/Element 3D/C4D to only show the one slice of an object that interferes with a set plane.
That would perfectly do the trick! :)


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Richard Garabedain
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 25, 2018 at 9:31:49 pm

Element 3d can definitely do that if youve got it?


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Roman Holtwick
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 26, 2018 at 1:36:45 am

I do have Element 3D!
But never used it for something like this.
How would you go about it? I only experimented with text in AE itself yet.

Also make sure to read the answer I posted to Steve above since there seems to be some major misunderstandings in what I want to do.

Thanks! :)


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Steve Bentley
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 26, 2018 at 5:16:52 am

Ok good that clears that up (we've made some LED sticks that do what I was describing, you wave them through the air and they create a still that just seems to hang there, so that's where my brain went).
I haven't played with booleans in Element 3D (I'm not even sure if it has them) but in C4D you would drag (animate) a "cutting" object through the object you want to slice, and both objects would be childed under a boolean object. Create a movie of every frame and voila, there's your growing or sliced cross section.
In your case, the cutting object could be a big cube with a slice out of it (a boolean in itself) so that the bulk of the cube makes the bulk of the other object disappear and only reveals the main text object's geometry in the slice.
The text object should be a shell object with wall thickness, otherwise the boolean is going to reveal a flat face at the cut point instead of an outline. (and a pure shell I don't think will show its edges as the faces techincally have no thickness). ONce you have a shell you can use the cloth tool to add thickness to the shell.
You might also be able to do this with a shader, but it would have to be a true 3D shader that goes all the way through the object. You could use the gradient shader available in each material (set to object space and 3d) to create a high contrast mask to revel the slice. I'm not sure if that gradient should be in the transparency channel or the alpha (the former I'm guessing) but it would depend on the shader.



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Kalleheikki Kannisto
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 26, 2018 at 7:30:00 am

In Element 3D you can use an animated texture with transparency to this effect. See attached. The blue text is not the effect, it is a reference layer that shows the position of the text. To see the effect, you need to preview. AE CC 2017, Element 3D V2.

12478_e3danimatedsweep.aep.zip

Kalleheikki Kannisto
Senior Graphic Designer


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Richard Garabedain
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 26, 2018 at 3:47:15 pm

you create 2 copies of element after you have your scene set up. then. on the top copy you go to camera settings in the element 3d tab and go to far and near cut off. adjust them so that you get only a slice of your 3d text in the middle. then make it a different texture lower the opacity and set blending mode to add..now you move your camera around and see that it makes a pretty good cross section


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Richard Garabedain
Re: Light Painting - show only cross sections of 3D objects for advanced light painting effects
on Jun 26, 2018 at 3:49:19 pm

you can even invert the geometry on the 2nd element layer so that we see the inside geometry of the object rather than the outside...You invert it inside the element 3d scene setup


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