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camera projection ray-traced vs classic 3D

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Mark Doctor
camera projection ray-traced vs classic 3D
on Aug 14, 2018 at 2:30:47 pm
Last Edited By Mark Doctor on Aug 14, 2018 at 3:47:27 pm

I've projected a photo on a white solid. Converting the photo and the solid to a 3D-layer and using a point-light to cast the photo on the solid. The photo only casts shadows and transmits 100% of the light and the white solid accepts shadows.

This scene works in the basic-3D world, it also works with ray-traced set to quality 1/draft. But it gets blurred with a setting above 1.

It seems that the photo at scale 1% and at a distance of 10 pixels from the light acts different, than a photo scale 10% at a distance of 100 pixels from the light. The latter one gets less blurred by the ray-traced setting.

So my question is, what causes the difference?


(P.S. Does the point-light get in ray-tracing a cubic dimension?, instead of a infinite small point without a surface)



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Andrew Somers
Re: camera projection ray-traced vs classic 3D
on Aug 14, 2018 at 4:50:59 pm

What are your MATERIALS settings for the white solid and the photo? While your at it, what are your settings for the LIGHT and the CAMERA?

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Mark Doctor
Re: camera projection ray-traced vs classic 3D
on Aug 14, 2018 at 6:34:08 pm

I've captured a screenshot with all the settings.

The Comp 1 is ray-traced. (6 samples sinds 20 samples didn't matter)
The Comp 2 is classic-3D.

The only way to improve the ray-traced version, is by increasing the image scale and decrease the distance between image and the screen.



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Andrew Somers
Re: camera projection ray-traced vs classic 3D
on Aug 14, 2018 at 7:03:41 pm

Can you screenshot your LIGHT and CAMERA settings too please, for the ray traced version only

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Mark Doctor
Re: camera projection ray-traced vs classic 3D
on Aug 14, 2018 at 8:13:17 pm

Hi sorry for lacking this information, but I didn't use any camera in this demo its the custom view of AE.
I just duplicated the comp and the ray-traced version uses the exact same light en doesn't offer any extra settings that I can show (i also couldn't make it fit my screen whiteout loosing more vital information).

I tested some other scenario and it seems that ray-tracing can't cast sharp shadows either!?



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Andrew Somers
Re: camera projection ray-traced vs classic 3D
on Aug 14, 2018 at 11:48:48 pm

"I didn't use any camera in this demo"


Hi Mark,

If you don't add a camera layer, the AE uses a default camera that may or may not have settings you want.

Add a camera layer and make sure "Depth of Field" is turned OFF. There might be some other camera settings that might need adjusting, I'll look when I'm back in the studio.

Cheers

A

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Andrew Somers
Re: camera projection ray-traced vs classic 3D
on Aug 16, 2018 at 10:28:18 am

To follow up Mark, I tried to recreate the issue — and couldn't till I read your post again about having the image at 1% scale. I see that the issue is identical for POINT and SPOT lights, and is NOT there with PARALLEL lights (notice also that parallel lights do NOT have a "shadow diffusion" setting).

Basically, a ray tracing engine creates depth-of-field, motion blur, and antialiasing by shooting several rays out of each pixel. As Stu Maschwitz puts it, the AE Ray Tracer is "a brute-force multi-sample renderer".

My assumption is that the "point" light is 1x1 pixel square. Considering the spot light looks the same, I imagine that the math there also starts with a 1x1 pixel light (this makes sense for computation, I'd venture that a 0x0 point would probably not be used due to computational difficulties or artifacts).

Consider that if you scale your image to 1%, that means that 100 x 100 pixels of your original image now fit in the same size area as that 1x1 point light. And when antialiasing is turned on, multiple rays are created.

So it would seem that even with the light's shadow diffusion set to 0.0, there is always *some* due to the anti-aliasing multi-ray-sample nature of the system, not to mention the "math precision" (or lack thereof) resulting from *both* scaling small and being very close to the light.

In an attempt to quantify this, I did the following experiment. I created a 100x100 checkerboard, where each square is 10x10. Then setup a scene where the white solid was 1000 from the point light. And then the checkerboard was various distances and scales from the light, with scale 100% being halfway between the light and the white solid.

The second test was just one square, set 5 from the light and zoomed in to show the detail, with only a minor scale change between 8% and 12%.

Here are the results:

   


Interpretation: I think this may indicate the point light sources is 1x1 pixels, because at 10%, each square is 1x1 of an unscaled pixel, and in this one each black square is a nearly solid dot, and it rapidly degrades as the scale/distance decreases. This is echoed on the right where at less that 10% (meaning the square is 1x1) it becomes a fading dot, but the square shape becomes more apparent as we go larger than that.


As to fixing the problem for your project - is there a reason you can't move the light farther back, or put the image layer closer to the white?

My suggestion would be to scale no smaller than 50%, and place the light and image as needed to accommodate that (or larger) scale. Alternately use a parallel light, though that might not work for the rest of what you are building.

Andrew Somers
VFX & Title Supervisor
http://www.GeneralTitles.com


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Richard Garabedain
Re: camera projection ray-traced vs classic 3D
on Aug 16, 2018 at 4:31:40 pm

Yes...scale matters. after effects does not like things too small...even when everything is small in relation


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Mark Doctor
Re: camera projection ray-traced vs classic 3D
on Aug 20, 2018 at 3:30:25 pm

As to fixing the problem for your project - is there a reason you can't move the light farther back, or put the image layer closer to the white?

My suggestion would be to scale no smaller than 50%, and place the light and image as needed to accommodate that (or larger) scale. Alternately use a parallel light, though that might not work for the rest of what you are building.


The whole thing is a bit more complex. I have a footage that has been camera tracked and is constantly being mapped to different white solids at the right perspective from different positions. This enables me to move around with a secondary camera close to the position of the "real-world-tracked-camera". In this scene we also find a 3D shape

The reason for the second cam is to zoom and shift the point of interest of the real-world-cam towards the 3D layer. The 2D solution of Just scaling the whole composition and animating the anchor-point, disables the "continuously rasterization" for the 3D shape and wasn't acceptable because of the extreme zoom.

I've dropped the camera-mapping because the projected slide intersects with the white solids. So I've turned the footage in a large 3D-layer in the background parented to the real-world-tracked-camera and kept the second cam for zooming. Loosing the options of a dolly towards the 3D-shape, depth of field and more accurate reflection mapping.


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Steve Bentley
Re: camera projection ray-traced vs classic 3D
on Aug 20, 2018 at 6:41:08 pm

This is in the same vein so I thought A) it might point out a limitation similar to yours and B) might bring out the answer for both.
We have a large 3D environment inside AE (sorry not large, massive! The rearward objects are some 60,000 units from the camera). It seems were being bitten by something similar.
A solid layer that is angled back away from camera covers a huge area and has a bezier mask on it. Near camera it's great, but off in the distance that crisp edged mask gets fuzzy, even with continually rasterize turned on.
Is that the supersampling and AA turning, in essence, a circle (scaled down really small) into a sqaure made by four dots?



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