Oops! Sorry! I mean to post a screen shot. If you select scene from the Instances panel you should see Effects above it. From there you can select any number of scene effects/options.
The Background will wrap all the way around the scene. You can use images, but if they aren’t spherical, you’ll get a line where Carrara joins them. You can tile images. This is also where you would use an HDRI if you want. Whatever you use for a Background will be reflected in any object that has reflection.
A note about HDRIs and the scene’s Background: If you want the light effect of an HDRI then you need to have Skylight enabled in the render room. If you want to use an HDRI, but not have it show up, use the Backdrop option to hide it, or use the Rennder Alpha Channel option in the Render Room. Don’t use the Pre-multiplied Alpha or it will show up. The Skylight will use whatever you have in the Backgound channel as a light source. Color, image map, HDRI, etc. The HDRI will be more dynamic. Skylight will also use the Realistic Sky which is under Atmosphere to generate lighting as well.
The Backdrop will only fill the window. To avoid distortion with the Backdrop, make sure that whatever image you use is the same aspect ratio as the final render. Images or colors or whatever in the Backdrop will not reflect in your scene objects. As mentioned above, you can use the Backdrop to mask out the Background, but if you use an image in the Backdrop in conjunction with a Realistic Sky under Atmosphere, the Backdrop will appear behind the atmosphere. Great for sci-fi scenes where you want a planet behind clouds and haze poking above the horizon.
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