Noise is random, signal is not.
If you compare multiple images of the same subject, you can take some of those pixels and determine what is true signal. Put all those 'corrected' pixels into one master image and we call it stacking. Stacking increase the signal to noise ratio. Stacking does not increase signal. It reduces noise.
tntcorp wrote:
why is there a need to stack astro-images; please explain?
There is no need per se, but by stacking you can reduce noise which inevitably creeps into each sub-frame. Many astro pictures, especially of faint deep sky objects, are the result of stacking hours worth of frames.
dgdg wrote:
Nice sky.
I never save or make any edits in DSS.
The very monochrome appearing DSS output image goes straight to PS. My pre-stack raw images will be a little higher than 30-40 for each channel. The DSS output is even higher. After adjusting RGB black point levels separately, it generally works fine.
If you want to make 3 different jpeg images available, I'll try to find time to stack and make simple post processing adjustments in PS to see if I can reproduce it or suggest you change your settings somewhere. It does not take too long for DSS to stack, then black point adjustments in PS.
Thanks, David. I'm off to work, but see what I can do later. Just to make sure that I understand you correctly: You don't press save to file in DSS, but just import the autosave.tiff file automatically generated by DSS straight to PS?
Once the final composite pops up (the very light grey scale looking image), I make no edits and click save to file.
Save as tiff 16bit, no compression, embed adjustments but do not apply them.
Funny you mention crashing. I got an out of memory error stacking one light. Oh well. I found rebooting and closing processes make for a shorter session.
Chris_88 wrote:
There is no need per se, but by stacking you can reduce noise which inevitably creeps into each sub-frame. Many astro pictures, especially of faint deep sky objects, are the result of stacking hours worth of frames.
thank you for the response. i was wondering how to handle random hot pixels from long exposures. :-)
