I saved some dark frames.
After completion, selected a dark frame to subtract and tried several images, keeping the scope cover on.
I tried snapshot, framing shot and live stack, all with the scope cover on.
I did not see much difference in the images with and without dark subtraction. It appears the bad pixels were still there.
What am I doing wrong?
Tom Dean
When are Dark Frames Subtracted?
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Re: When are Dark Frames Subtracted?
Hi,
Dark subtraction occurs before the image is displayed on screen or saved, so you should see the effects.
the best thing to do is to show the main histogram function during both the capture of the dark frames and while testing them. When the dark subtraction is active then you should see that both the mean and standard deviations of the channel values fall when dark correction is active due to the removal of the background level and of some of the thermal noise.
Some more things to be aware of:
* Make sure that the newly created dark has been selected - the filename for it should show up in the 'Subtract Dark' control in the camera controls. There is a checkbox in the Capture Dark window to select it automatically, but that may not be checked by default
* Make sure the offset/black level/brightness control for your camera is set high enough to ensure that the histogram peak for a dark frame is clearly separated from the left hand side of the graph
* Dark frames only really help with hot pixels that are stable - ie that appear in the same place from one frame to the next. Some hot pixels are stable like that, others show up at random from frame to frame, and you may still see those after dark correction. If you turn off dark correction and stretch the dark image a lot and watch a few frames go by, you will get an idea of the division between stable and random hot pixels for your camera.
cheers,
Robin
Dark subtraction occurs before the image is displayed on screen or saved, so you should see the effects.
the best thing to do is to show the main histogram function during both the capture of the dark frames and while testing them. When the dark subtraction is active then you should see that both the mean and standard deviations of the channel values fall when dark correction is active due to the removal of the background level and of some of the thermal noise.
Some more things to be aware of:
* Make sure that the newly created dark has been selected - the filename for it should show up in the 'Subtract Dark' control in the camera controls. There is a checkbox in the Capture Dark window to select it automatically, but that may not be checked by default
* Make sure the offset/black level/brightness control for your camera is set high enough to ensure that the histogram peak for a dark frame is clearly separated from the left hand side of the graph
* Dark frames only really help with hot pixels that are stable - ie that appear in the same place from one frame to the next. Some hot pixels are stable like that, others show up at random from frame to frame, and you may still see those after dark correction. If you turn off dark correction and stretch the dark image a lot and watch a few frames go by, you will get an idea of the division between stable and random hot pixels for your camera.
cheers,
Robin