The image calibration process in PixInsight will allow us to remove unwanted blemishes, vignetting, dust, noise, amp glow from our light images.
In this particular 180 second image of NGC 7023 – The Iris Nebula, you can see a few things:
- Vignetting: There is a darkening around the edges. This is specific to my imaging rig as I’m often using a focal reducer to try and speed up my F/10 telescope
- Donut: In the upper right, there is a very noticeable donut. Oftentimes, donut blemishes are caused by dust. Unfortunately for me, this particular donut is a scratch on my telescope’s corrector plate.
But after image calibration, we end up with the following
The image is much cleaner. This is why we take the time to create darks, dark flats and flat frames.
We need to calibrate each light frame with our master dark frame and our master flat frame.
- Master Dark: Should have the same temperate, binning, gain, offset and duration as the light frame
- Master Flat: Should have the same temperate, binning, gain, offset and filter as the light frame. Remember, the master flat image was corrected with a master dark flat with the same duration, which removed any electronic noise
We simply select the master dark and flat frame, making sure that calibrate and optimize are not selected. This is because
- Calibrate: This subtracts bias from the master dark (which we are not using) and subtracts bias and dark from the flat frame (which we did manually with our master dark flat images.
- Optimize: This tries to scale the master dark exposure duration with the light images. Because our master dark exposures are equal to our lights, this option is not required.
The next step is to take these images and run a PixInsight Cosmetic Correction.