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What is Pixel Mapping?
The CCD, CMOS, and NMOS sensors used as film in digital cameras are made up of millions of pixel sites that are microscopic photodiodes—charged electronic elements that respond to light. These pixels may cease to function over time or may not even be functional when the sensor is manufactured. There are two types on non-functioning pixels:
- Dead Pixels: A pixel that reads zero or is always off on all exposures. This state produces a black pixel in the final image.
- Stuck Pixels: A pixel that always reads high or is always on to maximum on all exposures. This produces a white pixel in the final image.
When a digital camera is manufactured, one of the quality control steps is Pixel Mapping. In this process the sensor is checked for dead or stuck pixels. When such pixels are found, a radial interpolation explores the pixels around the dead or stuck pixel, maps their locations, and inserts data enabling the camera to mimic what the dead or stuck pixel should be doing.
Over time, all sensors will develop dead or stuck pixels. They can be cloned out using image post-processing software, but this can be time consuming. The majority of camera brands require that the camera be sent to a service facility to have the sensor re-mapped by a technician, which can be costly and means the user will be without a camera while re-mapping is being done.
Olympus incorporates Pixel Mapping in the firmware of its digital cameras so that the user can perform Pixel Mapping as necessary or as preventive maintenance and not have to send the camera in to a service center to have the sensor re-mapped. We recommend once a year. Look in the menu for PIXEL MAPPING. The process only takes a few seconds. Some of the earlier Olympus models have Automatic Pixel Mapping (APM) that re-maps the sensor when the batteries are replaced.
Pixel Mapping will not repair dead or stuck pixels in an LCD screen—this requires that the LCD be replaced by repair.
“Hot Pixels” are not to be confused with dead or stuck pixels. A hot pixel is a pixel that reads high on longer exposures, and can produce white, red, orange, green, or yellow green in longer exposures. The longer the exposure (such as in night photography), the more visible the hot pixels. This phenomenon is caused by the sensor heating up during long exposures. When doing long exposures, use the NOISE REDUCT. option in the menu. When Noise Reduction is enabled, immediately after the initial exposure, the camera makes a second “dark frame” exposure of the same duration with the shutter closed to recreate only the hot pixels in an image. The camera then, in effect, digitally overlays the two images and subtracts the hot pixels in the dark frame image from the original exposure. This doubles the exposure time, so if the original image exposure time was two minutes, the dark frame exposure will be two more minutes for a total time of four minutes.
Archive - E-System:
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