Interline CCD

An interline-transfer CCD detector has a parallel register consisting of columns of sensors (photosites or pixels) separated by opaque strips (interline masks). The photons of the image accumulate in the exposed sensor area of the CCD detector.

Unlike conventional CCD cameras, which use a mechanical shutter to keep light from falling on the detector while the accumulated charge is being read out sequentially from the detector to your computer, the interline detector uses an electronic "shutter." During CCD readout the entire image is first electronically shifted from the sensor columns into shift register columns hidden under the interline masks between each row of pixels. All of the columns shift simultaneously from sensors to shift registers, rather than transferring sequentially, as with a conventional CCD. Readout then proceeds from the hidden shift register columns sequentially to your computer in normal CCD fashion while the now-empty sensor areas start to accumulate more photons.

Since the signal is transferred in microseconds, electronic pixel smearing during download (from photons continuing to be recorded while the pixel is being read) is undetectable for typical exposures. The rapid transfer also allows the interline CCD to act as an electronic shutter to permit very short, very accurate exposures for lunar and planetary imaging.

A drawback to interline-transfer CCDs has been their relatively poor sensitivity to photons, since a large portion of each pixel is covered by the opaque interline mask. Kodak interline CCDs use a microlens assembly over the pixel array to direct the light from a larger area down to each photosite to focus more of the incoming light on the individual pixels.

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