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The term "blooming" is used to describe the visible effects arising from the overflow of charge from one pixel to another in sensor of a digital camera. The phenomenon is potentially of serious concern with CCDs, where charge can flow along a column of pixels and create a distinctive white streak in an image. However CMOS sensors are more resistant to the effect. Sensory overflow can also cause affected images to appear over-exposed, lacking in contrast or even blurred. This is typically most apparent in strongly back-lit scenes.

Blooming can be reduced at the design stage by the introduction of a so-called "anti-blooming gates" which ease sensory overflow by bleeding away excess charge from saturated pixels. However, this design strategy represents a compromise as it also reduces the photosensitive area of each pixel, reduces effective resolution by increasing the gap between adjacent columns of pixels, and is effective only under less-well-lit situations. Such gates are consequently not normally used in extreme low light applications. Some of the visual effects of blooming can be used to achieve interesting effects, particularly where mysterious or ethereal images are required.

Note that blooming should not be confused with purple fringing, a term used to describe the presence of a blurred purple ghost image which may also appear in high-contrast back-lit scenes.


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