Bloom

Bloom is an effect used to reproduce an imaging artifact of real-world cameras. The effect produces fringes of light extending from the borders of bright areas in an image, contributing to the illusion of an extremely bright light overwhelming the camera or eye capturing the scene.

Lens Dirt applies a fullscreen layer of smudges or dust to diffract the Bloom effect. This is commonly used in modern first person shooters.

Properties

Bloom settings:

Property	Function
Intensity	Strength of the Bloom filter.
Threshold	Filters out pixels under this level of brightness. This value is expressed in gamma-space.
Soft Knee	Makes transition between under/over-threshold gradual (0 = hard threshold, 1 = soft threshold).
Clamp	Clamps pixels to control the bloom amount. This value is expressed in gamma-space.
Diffusion	Changes extent of veiling effects in a screen resolution-independent fashion.
Anamorphic Ratio	Emulates the effect of an anamorphic lens by scaling the bloom vertically (in range [-1,0]) or horizontally (in range [0,1]).
Color	Tint of the Bloom filter.
Fast Mode	Boost performances by lowering the effect quality.

Dirtiness settings:

Property	Function
Texture	Dirtiness texture to add smudges or dust to the lens.
Intensity	Amount of lens dirtiness.

Details

With properly exposed HDR scenes, Threshold should be set to ~1 so that only pixels with values above 1 leak into surrounding objects. You’ll probably want to drop this value when working in LDR or the effect won’t be visible.

Performances

Lowering the Diffusion parameter will make the effect faster. The further away Anamorphic Ratio is from 0, the slower it will be. On mobile and low-end platforms it is recommended to enable Fast Mode as it gives a significant boost in performances.

Finally, smaller lens dirt textures will result is faster lookup and blending across volumes.

Requirements

• Shader model 3

See the Graphics Hardware Capabilities and Emulation page for further details and a list of compliant hardware.