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Lighting a scene with an HDR background is pretty well documented. But some 360 cameras can also shoot HDR movies.

Is it possible to import a HDR movie into the background of a Cycles or Eevee scene using the World settings? If so, how?

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    $\begingroup$ If it's a supported format, then simply by opening it like you would with a regular (single) HDRI. $\endgroup$ – Robert Gützkow Dec 29 '19 at 10:20
  • $\begingroup$ Sadly, it's not that simple. Yes - an EXR sequence can be brought into Blender. But there's a bunch of stuff that needs to be done to make it work. I brought a sequence in, but each frame wasn't of the required bit depth. Then, when I brought a sequence of the right bit depth in, it didn't have enough resolution, or the colors weren't right, or the shadows were inconsistent. It's tricky. $\endgroup$ – OroNZ Dec 30 '19 at 4:59
  • $\begingroup$ That's not an issue with Blender though, but rather with your footage. Blender can only display/use the image data that is in the file. If the bit depth or resolution is to low, then that's caused by the image file not containing these information. $\endgroup$ – Robert Gützkow Dec 30 '19 at 15:40
  • $\begingroup$ It gets to be an issue with Blender when you consider filesize. Let's face it: I could light a scene with a 512x256-pixel 8-bit JPEG if I wanted to. The results will be indistinct, over-saturated and uncontrollable, but it's possible. However, if I want the scene to be lit with the same movie I'm using as a background plate, it's not possible to get a serviceable movie running. Blender will crash. I have a 10-core CPU, twin-GTX1080s and 128GB RAM. Even with that kind of power, Blender crashes with that amount of data to manipulate. $\endgroup$ – OroNZ Dec 30 '19 at 18:39
  • $\begingroup$ It shouldn't crash. I routinely use 8k or 16k, 32-bit .exr to light scenes. Image sequences should be allocated as needed and not all at once as far as I'm aware. Are you running out of memory or does Blender simply crash for no apparent reason? $\endgroup$ – Robert Gützkow Dec 30 '19 at 19:03
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After a lot of experimentation, the answer is Yes, but the results aren't great, for a few reasons. I'm going to use HDR footage from the Insta360 ONE X for reference, not because it's particularly great at HDR movies, but it's pretty popular, and the results from other cameras in this price range (and higher) will be about the same.

1. Low dynamic range

360 HDR movies shot on action cams do yield High Dynamic Range movies, but we're talking about a pretty low end of 'High' here. Users of the popular HDRI resource HDRI Haven will be used to HDRIs with 15, sometimes 26 EV (Exposure Values) of dynamic range. This produces very accurate lighting results, delivering excellent shadow quality and color. The ONE X will get you 3 EV... 4 EV tops... delivering soft shadows and saturated lighting.

2. Low Resolution

enter image description here

This scene features an outdoor Insta360 ONE X frame from an HDR movie. (A disclaimer first: The yellow rectangle features some settings that I wouldn't recommend or consider good practice, but it does eke out better contrast in the scene to get more pronounced shadows.)

Even so, you can see that the background plate is pretty blurry. this is due to camera movement and because the equirectangular image is just 2880 x 1440 pixels - the native dimensions from the camera. And we're only seeing about a third of those pixels in the background - the other two-thirds are out-of-shot, wrapping around the rest of the 'World'.

3. Soft Shadows

The green circles point out the difference between the sharp, full-sun shadows in the footage, compared to the soft, indistinct shadows in the scene. There's also an excessive amount of blue coloration from the sky on the white plane. (Ignore the slight pink coloration under the ball; that's ambient light from my hand, holding the camera).

4. Shake

Ideally, each frame of an HDR movie has multiple bracketed shots from a single point in time and space. If the camera's moving, this isn't possible. In the shot above, I was walking under an arch. The blue circle indicates blurred building lines due to camera movement and shake. This shake also impacts dynamic range, due to a difference in camera position between when it took its low bracketed shot to its high bracketed shot of that frame. If the shots don't overlap exactly, lighting becomes indistinct and colors aren't computed accurately.

Summary

Live HDR footage can give you, quite literally, quick and dirty background plates. You can mitigate problems by using a stationary camera and low-contrast, cloudy days. If you need a motion background plate (driving scenes when people are in cars, for instance), the low-res background could be blurred, with in-scene constraints used to blur in the right directions, depending on camera angle.

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