HDRi skies only use part of the HDRi image

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Permalink Reply by Render Plus on February 11, 2011 at 9:01am

 

HDRI skies don't work well for backgrounds unless you have a very high resolution HDRi, or use a very large Field of View.

If you use a standard FOV of 35, then you're only using 10% of the width of the HDRi image and stretching part of the image that across the background of your rendering.  (35 degrees is about 10% of 360 degrees)

So if you do the math, for a 1000 pixel rendering, you would need a 10,000 pixel HDRi image for a 35 degree FOV to render at highest quality.

If the FOV is small, it will look like you are zoomed in on the background image, the wrong scale. So it's better to use a larger FOV for exterior scenes for which you want to use a HDRi sky for the background.

If you set the FOV to 90, then you will see 1/4 th of the HDRi image as a background. That kind of works, but of course you may get distortion from the 90 FOV in the perspective view. 2 Pt Perspective may help with this.

Here I used StJohns_09_2.hdr, one of the highest resolution HDRi files that are included with the librairies. It has a width of 4096 pixels. And I used a FOV of 90 and turned on 2 pt perspective.


So it's using about 1/4 of the entire HDRI image:

(This is hard to see here because this is a flat representation of a Panoramic HDRI Image)

 

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Permalink Reply by Render Plus on February 11, 2011 at 9:22am

Here is another sample with a 90 degree FOV for an exterior - without 2 PT Perspective.

(Using the Bear Mountain HDRi from our library)

 

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