Bryce adapts the grey-values to the size of the scene, so the size of your objects shouldn't affect the usability of this feature. I used distance renders on some of my images for haze or some other effects. It's just about as fast as maskrenders, but it's still possible to slow it down. I made a tunnel with 15.800 primitives and it took more then 2 hours to make a distance render at 675x900.

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