=====Dark frame=====

With some camera it is difficult to use a [[bad pixel map]] to cleanup the auto-focus frames. In this case you can define here a dark frame that will be subtracted to remove the hot pixels.\\
Beware this processing require the dark frame is acquire with the same gain and offset than the auto-focus frames. This also use more resources than the bad pixel map processing. So the bad pixel map must be used in preference if applicable.

This same dark frame is also used with the [[preferences#camera]|image stacking]] option. 

Use the menu **File → Dark frame → Apply to current image** if you want to subtract the dark from the currently displayed image.\\
You can identify an image that was dark subtracted with a comment at the end of the FITS header.

====Information====

This menu show information about the current dark frame, the exposure time and the size of the image, you can also see the dark file FITS header for more details.

You have two options to define the dark frame, using the camera directly or using a processed dark frame. The second option is preferred because the processed dark as less noise.

====Create from the camera====

Procedure:

  - Camera should be connected and cooling on if available.
  - Set the required binning, gain, offset in [[preview|Preview tool]]. Use the same settings as for the focus and slewing
  - Cover the camera or telescope. If your camera has a shutter it will remain closed during the exposure.
  - Select menu **File → Dark frame → Create from camera** \\ {{:en:documentation:multi-dark.png?250}}
  - Select if you want a single or multiple exposure. A dark will be taken and saved for future use.

====Load a dark file====

Select menu **File → Dark frame → Load dark file**\\
Select the dark file from the file dialog.\\
The file must be taken with the same binning, exposure time, temperature than used for auto-focus. This file must use a pixel format of 16bit.


====Clear Dark frame====
To remove/clear the dark frame select the menu **File → Dark frame  →  Clear Dark frame**

====Check the dark frame==== 
Take a preview image, select the menu **File → Dark frame → Apply to current image**\\
Verify the hot pixels are removed and the processing do not create unwanted artifact.