Bias frame
Encyclopedia
In digital photography
, a bias frame is an image obtained from an opto-electronic image sensor
, with no actual exposure time. The image so obtained only contains noise due to the electronics that elaborate the sensor data, and not noise from charge accumulation (e.g. from dark current
) within the sensor itself.
A bias frame is complementary to a dark frame, which has a charge integration time but in darkness.
Since a dark frame contains noise including a fixed-pattern noise
component, some of which corresponds to the bias frame, and some of which is due to dark current and is proportional to the exposure time, it is possible to obtain an image representing only the dark-current component by subtracting a bias frame from a dark frame. The resulting image allows obtaining an "artificial" dark frame when multiplied by a factor depending on exposure time and then added back to the bias frame. Although this technique is less accurate than shooting a dark frame for each specific exposure duration, it has the advantage of drastically reducing the time needed to obtain dark-frame data for dark frame subtraction
.
Digital photography
Digital photography is a form of photography that uses an array of light sensitive sensors to capture the image focused by the lens, as opposed to an exposure on light sensitive film...
, a bias frame is an image obtained from an opto-electronic image sensor
Image sensor
An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices...
, with no actual exposure time. The image so obtained only contains noise due to the electronics that elaborate the sensor data, and not noise from charge accumulation (e.g. from dark current
Dark current
Dark current is the constant response exhibited by a receptor of radiation during periods when it is not actively being exposed to light. It may refer to:...
) within the sensor itself.
A bias frame is complementary to a dark frame, which has a charge integration time but in darkness.
Since a dark frame contains noise including a fixed-pattern noise
Fixed-pattern noise
Fixed pattern noise is the term given to a particular noise pattern on digital imaging sensors often noticeable during longer exposure shots where particular pixels are susceptible to giving brighter intensities above the general background noise....
component, some of which corresponds to the bias frame, and some of which is due to dark current and is proportional to the exposure time, it is possible to obtain an image representing only the dark-current component by subtracting a bias frame from a dark frame. The resulting image allows obtaining an "artificial" dark frame when multiplied by a factor depending on exposure time and then added back to the bias frame. Although this technique is less accurate than shooting a dark frame for each specific exposure duration, it has the advantage of drastically reducing the time needed to obtain dark-frame data for dark frame subtraction
Dark frame subtraction
In digital photography, dark-frame subtraction is a way to minimize image noise for pictures taken with long exposure times. It takes advantage of the fact that a component of image noise, known as fixed-pattern noise, is the same from shot to shot: noise from the sensor, dead or hot pixels...
.