2 questions about HDRI

  1. I know how to add an HDRI image to my scene, but how can I have that image be used while at the same time having a different image that’s actually visible in the background?

  2. I would like to create artificial HDRI maps. I know for example that I can create a gradient from black to white and then I can add a white disc to represent the sun and render it out and save as a .hdr file. Then I can add the image the same way I would add any other HDRI map. What would be the best and most accurate way to actually do this. I tried once, but I was very disorganized, so I’m hoping someone maybe can give a quick explanation on the best way to do this.

As you can guess from the 2 questions, I’m trying to create realistic lighting, while at the same time, I would like to maintain an artificial set. Once I get this right, I can experiment with the gradient and perhaps try different patterns to see how I can offset the lighting, but first I need to make sure I understand how to get it done.

For the render, I use Cycles and I am setting the camera to Equirectangular.

You can either render with transparent background and add e .g. a backplate image in post-production…

…or use the light path node to switch backgrounds for the camera:

Anything in particular you want to know?

To create HDRI you have to put your camera in Panorama -> Equirectangular.
Once rendered, the image must be saved in any format that accepts 16 bits or more (32 is best). It doesn’t have to be in the .hdr format by the way.

The Light Path, works great, thank you.

I guess the only other question I have is about the quality of the hdr. Even if it is not visible, because I use a different background image to show, what would be the best resolution for the hdri. I mean if it’s a gradient, do I want to make it 200% of 1080p for example? Is there a good way to judge this.

And a related question. If HDRI photos carry extra image information. How does an artificial hdri that I create myself carry extra data? I mean a render is a render, there is nothing that says there is more data? I might not be completely grasping the concept yet.

Cycles’ renders are internally 32 bit HDRI images, so they already carry that little bit of extra information. As soon as you save that out to a format that can preserve this information, you will be good to go.

One piece of that extra information is the dynamic range, the additional brightness information that can really light your scene. So, place your lamps/luminous polygons etc. in the scene like you would without an HDR, assign the appropriate emission intensity to them, render that out as an equirectangular map and save as .exr/.hdr. Bingo!

If you use that environment HDRI only for lighting, too much resolution can actually increase the chance of fireflies. In fact, you may want to even additionally blur a “light only” HDRI environment in Photoshop (or Blender’s compositor).

Ok, I think I got it. This node setup is working great. I added a brightness node to the HDRI node to brighten the overall illumination. There is something a little complicated. The reflection I get is of the HDRI. Is there a way to avoid the reflection just like the background of the HDRI, but still get it’s illumination? In other words, I want the reflection of the background also instead of the HDRI.

Same node setup…:smiley:
Just tell Cycles to use that other environment for camera and reflection (or glossy or…) rays:

Could of course also be a third map: One for the camera, one for lighting and one for reflections…

Sky .JPG visible to camera and reflections, lighting from studio .HDR…