AndyBooth wrote:Hi there,
Bit of advice on best way to redeem a stack with some guiding errors (small trails).
I know that the repair module makes the stars round again, but does it also try and restore the trailed DSO object also?
Or is deconv module best for this?
Guess what i'm looking for is a Deconv where you specify the trailed star, and the module deconvolves back to an ideal star profile.
Is this possible?
Thanks for any help
Best regards,
Hi Andy,
You are right in that, technically, this is possible. However results in practice are never very good, unless the tracking error is very, very slight.
There are a number of reasons for this being so challenging;
- Determining the correct profile (point spread function or 'PSF') can be challenging.
- Ringing artifacts are hard to repair around overexposing objects such as stars. Such objects may still exhibit elongation as a result, or, if no de-ringing is performed, then ringing will be very prevalent.
- The 'distortion' must be absolutely uniform throughout the image for this to work (i.e. you can't have coma) - the PSF must be the same for all pixels in the image.
- Noise must be low, or the regularization may leave trails.
Some of the above are also true for deconvolution with a Gaussian profile/PSF (which approximates very well how atmospheric turbulence randomly spreads photons around). The nice thing about a Gaussian profile (and its reverse) though, is that mismatches in the profile are a little bit less visible, because of its non-directional error spreading characteristics. De-ringing is also much easier if the PSF is assumed to be non-directional.
If your image suffers from something that can be addressed through fixing your hardware (flexure, polar alignment) or changing acquisition characteristics (focus, exposure length or focal length), then try to address such things in hardware. Only as a last resort, try fixing things in software!
Do you know what is causing the tracking errors?
