Filters for Removing Artifacts

Artifacts in CCD images generally include dead pixels--where the pixel has little or no sensitivity to light--or hot pixels--where a pixel has too much noise or has been hit by a cosmic ray (a high-energy particle entering Earth's atmosphere from space).  Median-combining images tends to cancel out many of these artifacts.  But if they cannot be removed this way, or if they remain afterwards, there are filters which can help remove them.

Many of the CCD image processing programs have routines for automatically removing artifacts.  The image below contains both dead pixels and hot pixels.

Above:  Bright and dark artifacts in a portion of an unprocessed image of M106.  Two hot spots and one cool spot are circled.

Running the Remove Dead Pixels function in CCDOPS eliminates the cool spot.

Above:  Same image after dead pixels have been removed.

Running the Kill Warm Pixels routine does the same to the hot spots.

Above:  Image after removal of bright and dark artifacts.

Some routines work better than others, and large defects will need to be removed by using the Clone tool (or Healing Brush) in Photoshop or a similar function in another program.  See the Photoshop pages of the Software Instructions section for more details.

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