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Bad/Hot pixel map

The bad pixel map will prevent the auto-focus or slewing function locking on a hot pixel rather then on a star.

The bad pixel map will be only applied on preview images, focus or slewing images. It is not applied on captured images. Those images are not altered.

Use the menu File → Bad pixel map → Apply to current image If you want to apply the bad pixel map to an image you load in the program.


  1. Camera should be connected and cooling on if available.
  2. Set the required binning in Preview tool. Us the same binning as for the focus and slewing
  3. Select an exposure time between 10 and 60 seconds.
  4. Cover the camera or telescope similar as taking a dark image. If your camera has a shutter it will remain closed during the exposure.
  5. Select menu File → Bad pixel map → Create bad pixel map
  6. Click Continue. A dark will be taken and number of hot pixels will be reported in the log window.

Take a preview image and check if the bright hot pixels are surpressed.

To remove/clear the bad pixel map select the menu File → Bad pixel map → Clear bad pixel map

Error: If you get an error message: “too many hot pixels”, increase the sigma threshold value in the menu Edit → Preferences → preview options. If successful the program log will report the number of hot pixels suppressed.

A typical threshold value is 5 for CCD and 8 for a modern CMOS sensors. Decrease the threshold value if you want suppress more hot pixels. Normally you should surpress maybe 5 to 30 hot pixels but you can go much higher.

en/documentation/bad_pixel_map.txt · Last modified: 2018/02/15 10:49 by pch