pavelsevecek

Physically Based Bloom

Added 2023-10-16 07:00:04 +0000 UTC

Next major update will include improvements to the bloom effect - the glow around stars and other hot objects.

Previously, the glow was done by a simple Gaussian blur of the pixels containing hot particles. This meant the radius of the glow was only a few pixels and independent of the particle intensity, making it very localized and simply unrealistic. In the new version, the existing filter is being replaced with a physically based bloom, based on this article. It is achieved by successive downscaling and upscaling of the image, making the radius of the glow much larger - potentially the entire image. The effect also correctly responds to the intensity of input pixels and to the camera settings, exposure and compression.

The result is immediately much more realistic. Compare it yourself on the examples below.

Planetary impact

Glow of stars

The bloom facelift also comes with a bunch of knobs and turns you can use to get the desired result. In addition to the existing bloom intenstity, there is the bloom threshold, used to tweak the intensity of pixels that contribute to the glow, and the bloom falloff, which determines how the bloom intensity changes with the distance from the hot pixel.

The gif ruins the image colors, but hopefully you can see the difference - higher falloff makes the bloom less strong towards the center and more extended outward.