Because the bright regions are extended in both width and height due to the blur filter, the bright regions of the scene appear to glow or bleed light.īloom by itself isn't a complicated technique, but difficult to get exactly right. This blurred texture is added on top of the original HDR scene texture. The resulting blurred texture is what we use to get the glow or light-bleeding effect. The strength of the bloom effect is largely determined by the range and strength of the blur filter used. We then take this thresholded brightness texture and blur the result. This gives us an image that only show the bright colored regions as their fragment intensities exceeded a certain threshold: We take this HDR color buffer texture and extract all the fragments that exceed a certain brightness. If we were to render this to an HDR color buffer the scene looks as follows: The colored light cubes have a brightness values between 1.5 and 15.0. We render a scene filled with 4 bright light sources, visualized as colored cubes. Let's illustrate this process in a step by step fashion. This extracted brightness image is then blurred and the result added on top of the original HDR scene image. To implement Bloom, we render a lit scene as usual and extract both the scene's HDR color buffer and an image of the scene with only its bright regions visible. It is simply that HDR makes Bloom more effective to implement (as we'll later see). It is possible to implement Bloom with default 8-bit precision framebuffers, just as it is possible to use HDR without the Bloom effect. They are however completely different techniques used for different purposes. A common misconception is that HDR is the same as Bloom as many people use the terms interchangeably. When done in a subtle fashion (which some games drastically fail to do) Bloom significantly boosts the lighting of your scene and allows for a large range of dramatic effects.īloom works best in combination with HDR rendering.

An example of a scene with and without glow can be seen below (image courtesy of Epic Games):īloom gives noticeable visual cues about the brightness of objects. Bloom gives all brightly lit regions of a scene a glow-like effect. This light bleeding, or glow effect, is achieved with a post-processing effect called Bloom. This effectively gives the viewer the illusion these light sources or bright regions are intensely bright. One way to distinguish bright light sources on a monitor is by making them glow the light then bleeds around the light source.

Bright light sources and brightly lit regions are often difficult to convey to the viewer as the intensity range of a monitor is limited.

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