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Author Topic: Problem with stereo rendering: Common vs. Rectilinear lense (v189)  (Read 2282 times)
Description: Rectilinear lense should be used when stereo images or animation are rendered.
0 Members and 1 Guest are viewing this topic.
Posts: 156

« on: January 11, 2014, 10:12:14 PM »

Hello Jesse and all stereo fractalist,

Jesse, my feature request:
Display a warning when the user wants to render a stereo image or video while using the "Common" lense type.

The details:
After calculation of my "Living Planet" stereo video was finished I noticed a problem:
Points that should match for left and right eye (the spikes) don't have the same vertical position. It is not that much, but still kills the 3D effect a bit.

See the following snapshot from the "Living Planet" animation:

It's the anaglyph of frame 275. I connected matching spikes from red to blue image. Usually this should always create horizontal lines. But because of the vertical shift the lines became boxes. The higher the box, the bigger is the vertical shift (the error).
As you can see the error is biggest in the edges and not present at the center / points on Y-axis.

I thought a bit about optical laws and decided that this is no bug but the normal result when two eyes were looking at a fixpoint.
When the fixpoint is infinity then the problem is nearly nonexisting because the rays reaching the eye are quite parallel. But near fixpoints create more and more crossed rays.
Crossed rays have the result, that the canvas / the image of the left eye and the one from the right eye are canted (rotated around Y-axis) to each other.

Another testrender proved this.

Here the right eye image:

Here the left eye image:

Green encircled are good comparable areas.
Blue lines are the length of compared points to the border, so their vertical position. Usually lines from corresponding point should have the same length. But they haven't.
Red arrows show the direction the left eye canvas is canted (rotated around Y-axis) to the right eye canvas.

Well, the canted canvases are the result of the optical laws when looking at a fixpoint. I think that our eyes have the same "problem", but we don't notice this, because the areas near the border of our field of view can not be seen sharp.

Points near the camera are more effected than points far away.
Near the left and right border we have the strongest effect/error.
The higher the FOVy the stronger the effect/error.

While playing and testing I also tried the camera lense setting "Rectilinear" and "Yeah" grin this solved the problem.
Even at a high test FOVy value of 150 the "Rectilinear" setting produce a perfect stereo image, even when such a FOVy is a bit too heavy for "Rectilinear" mode.

So boys and girls:
Use "Rectilinear" lense (for both eye images) when you plan a stereo video or image rendering!
 Please Read

Fractal Fertilizer
Posts: 374

« Reply #1 on: July 08, 2016, 05:52:59 AM »

Wonderful explanation. Kudos!
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