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Hubble Space Telescope
Hot and Cold Pixels

Hot and Cold Pixels



Hot pixels are pixels with excessive charge compared to the surrounding pixels, while cold pixels are less sensitive than the surrounding pixels or have no sensitivity. Many of these pixels were identified during the SLTV test performed on the ground in August 1996. During calibration, the flag values from the static bad pixel mask file are added to the Data Quality (DQ) image. The MASKFILE calibration reference file contains a flag array value for every pixel. A flag of 32 identifies known bad pixels. The number of these bad pixels is quite small, less than 0.2% of the 65536 pixels in an array. Currently, the MASKFILE is made from pre-launch data and is not up to date.

An example of bad pixels can be seen in the flat field or the dark current images. In this example, they are manifested as white spots in the dark current images above.


As with grot, the best way to minimize the effect of hot or cold pixels is to dither your observations, and let CALNICB ignore the effected pixels upon recombination of the images.