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An example of bloom in a computer-generated image (from Elephants Dream.) The light on the bright background bleeds on the darker areas, such as the walls and the characters.
An example of bloom in a picture taken with a camera. Note the blue fringe that's particularly noticeable along the right edge of the window.

Bloom (sometimes referred to as light bloom or glow) is a computer graphics effect used in computer games, demos and high dynamic range rendering (HDR) to reproduce an imaging artifact of real-world cameras. The effect produces fringes (or feathers) of light around very bright objects in an image.

Contents

Theory

The physical basis of bloom is that, in the real world, lenses can never focus perfectly. Even a perfect lens will convolve the incoming image with an Airy disc (the diffraction pattern produced by passing a point light source through a circular aperture) [1]. Under normal circumstances, these imperfections aren't noticeable; but, an intensely bright light source will cause the imperfections to become visible. As a result, the image of the bright light appears to bleed beyond its natural borders.

The Airy disc function falls off very quickly but has very wide tails (actually, infinitely wide tails). As long as the brightness of adjacent parts of the image are roughly in the same range, the effect of the blurring caused by the Airy disc is not particularly noticeable; but in parts of the image where very bright parts are adjacent to relatively darker parts, the tails of the Airy disc become visible, and can extend far beyond the extent of the bright part of the image.

In HDR images, the effect can be re-produced by convolving the image with a windowed kernel of an Airy disc (for very good lenses), or by applying Gaussian blur (to simulate the effect of a less perfect lens), before converting the image to fixed-range pixels. The effect can't be fully reproduced in non-HDR imaging systems, because the amount of bleed depends on how bright the bright part of the image is.

As an example, if a picture is taken indoors, the brightness of outdoor objects seen through a window may be 70 or 80 times brighter than objects inside the room. If exposure levels are set for objects inside the room, windows will be bright enough, when convolved with the Airy disc of the camera being used to produce the image, to cause the image of the windows to bleed past the frames of the window.

Use

Use of bloom in computer graphics appeared in demos decades before it entered commercial games. Because of the hardware requirements of the Fourier transform needed to do HDR imaging, many demos use other techniques to implement bloom. However this is becoming less common with modern hardware. It has a reputation for being a visual boost on high-end demos, and has the advantage of taking focus away from uninteresting areas. It has therefore become an often used way of covering up low detailed areas, often due to the demogroups hardware, comporules or skill limitations for this particular demo.

The effect is popular in current generation games, and is used heavily in PC, Xbox 360 and PlayStation 3 games as well as the popular Nintendo GameCube and Wii release, The Legend of Zelda: Twilight Princess. Current generation gaming systems are able to render 3D graphics using floating point frame buffers, in order to produce HDR images. To produce the bloom effect, the HDR images in the frame buffer are convolved with a convolution kernel in a post-processing step, before converting to RGB space. The convolution step usually requires the use of a large gaussian kernel that is not appropriate for realtime graphics, causing the programmers to utilize approximation methods.[2]

The Afterimage effect is sometimes used to enhance the bloom effect.

Bloom became very popular after Tron 2.0 and is used in many games, modifications, and game engines, including Quake Live, Cube 2: Sauerbraten, Nexuiz, OGRE and Sylphis3D. Ico was one of the earliest games to use the bloom effect.[3]

See also

References

External links


.) The light on the bright background bleeds on the darker areas, such as the walls and the characters.]]

Bloom (sometimes referred to as light bloom or glow) is a computer graphics effect used in computer games, demos and high dynamic range rendering (HDR) to reproduce an imaging artifact of real-world cameras. The effect produces fringes (or feathers) of light around very bright objects in an image.

Contents

Theory

The physical basis of bloom is that, in the real world, lenses can never focus perfectly. Even a perfect lens will convolve the incoming image with an Airy disc (the diffraction pattern produced by passing a point light source through a circular aperture) [1]. Under normal circumstances, these imperfections aren't noticeable, but an intensely bright light source will cause the imperfections to become visible. As a result, the image of the bright light appears to bleed beyond its natural borders.

The Airy disc function falls off very quickly but has very wide tails (actually, infinitely wide tails). As long as the brightness of adjacent parts of the image are roughly in the same range, the effect of the blurring caused by the Airy disc is not particularly noticeable; but in parts of the image where very bright parts are adjacent to relatively darker parts, the tails of the Airy disc become visible, and can extend far beyond the extent of the bright part of the image.

In HDR images, the effect can be re-produced by convolving the image with a windowed kernel of an Airy disc (for very good lenses), or by applying Gaussian blur (to simulate the effect of a less perfect lens), before converting the image to fixed-range pixels. The effect can't be fully reproduced in non-HDR imaging systems, because the amount of bleed depends on how bright the bright part of the image is.

As an example, if a picture is taken indoors, the brightness of outdoor objects seen through a window may be 70 or 80 times brighter than objects inside the room. If exposure levels are set for objects inside the room, windows will be bright enough, when convolved with the Airy disc of the camera being used to produce the image, to cause the image of the windows to bleed past the frames of the window.

Use

The effect is popular in current generation games, and is used heavily in PC, Xbox 360 and PlayStation 3 games as well as the popular Nintendo GameCube and Wii releases, The Legend of Zelda: Twilight Princess, Metroid Prime, and Metroid Prime 2: Echoes. Current generation gaming systems are able to render 3D graphics using floating point frame buffers, in order to produce HDR images. To produce the bloom effect, the HDR images in the frame buffer are convolved with a convolution kernel in a post-processing step, before converting to RGB space. The convolution step usually requires the use of a large gaussian kernel that is not appropriate for realtime graphics, causing the programmers to utilize approximation methods.[2]

The Wii game Little King's Story also utilizes the effect to give the game a fantasy look, which combines storybook elements and colorful environments.

The Afterimage effect is sometimes used to enhance the bloom effect.

Bloom became very popular after Tron 2.0 and is used in many games, modifications, and game engines, including Quake Live, Cube 2: Sauerbraten, Nexuiz, RuneScape and Sylphis3D. Ico was one of the earliest games to use the bloom effect.[3]

See also

References

External links








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