Bloom (shader effect)

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Comparison of bloom effect, from Nexuiz. On left, bloom is turned off, on right, it's on. Note how bright-coloured objects are shinier, and how the lit part of walls are more blurred than the parts that are in shadow.

Bloom (sometimes referred to as Light bloom) is a computer graphics shader effect used by computer games.

In high dynamic range rendering (HDR) applications, it is used when the necessary brightness exceeds the contrast ratio that a computer monitor can display.

Blooming "spreads" out a light source. For example, a bright light in the background will appear to bleed over onto objects in the foreground. This effect is achieved by multiplying the image of the screen (lighten lighter areas and darken darker areas,) blurring the image, and drawing it over top of the original image. If there's a light source that is "brighter" than what the monitor can show, light blooming helps to create an illusion that makes the object appear brighter than it is, but at the cost of softening the scene.

The reason blooming is used alongside HDR is that when a saturated LDR image is blurred, the result is equivalent to blurring an image with lots of white areas, simply because values above 1.0 aren't preserved, so bright areas blur to gradients in the range of 1.0 -> 0.0. The result is simply a linear white to black gradient, regardless of the original color of the bright part. HDR, on the other hand, preserves colors above 1.0, so the blur results in a gradient between the saturated value that slowly becomes less and less saturated. A bright blue light may appear white at its center, but with HDR it retains the blue color in a halo around it when the image is blurred.

A common misconception is that a game that uses a bloom filter uses HDR. This is untrue, however, as blooming is often used alongside HDR, but is not a component of HDR.

The Afterimage (shader effect) is sometimes used to enhance the Bloom effect.

Bloom became very popular after Tron 2.0 and is used in many games and modifications. Ico was one of the earliest games to use the bloom effect.^[1]

Bloom lighting is now sometimes considered overused and cliche, reminiscent of the overusage of lens flare effects in early 3D-accelerated computer games.