stacking

[hobbit]

I am having a lot of trouble trying to stack my images in either ccd stacker, deep sky stacker or pixinsight. The individual images whilst not great are at least recognisable. When I try stacking them it's pretty much just a black screen with a couple of stars.

If I upload the original fits files could someone more experienced have a go and see if they get the same result or if it's just me doing something wrong?

Pete.

[RickS]

A black screen with a couple of stars in PixInsight often means you haven't done a screen stretch on a linear image. Try typing CTRL-A.

I'd be happy to take a look at your FITS files if you like...

Cheers,
Rick.

[hobbit]

removed file link due to possible virus

[RickS]

Got the files OK. Will have a play with them tonight.

[RickS]

No problems stacking in PixInsight. As I suggested, the files are linear (not stretched) so you need to do a screen stretch to see what is there after stacking them.

What I did was:


StarAlignment to register the images against a reference image (I picked "Calibrated-Color-T3-pb8010-ngc6960-20131129-203221-Color-BIN1-W-300-001" at random. Normally, I would go to some trouble to pick a good image as the reference. All other parameters were the default. The aligned images are written to a directory.
ImageIntegration to stack the registered images. I used the default parameters and selected Winsorised Sigma Clipping as the rejection algorithm (it is generally a good choice for a dozen or so subs). I set Sigma low at 4.0 and Sigma high at 3.0. Normally, I would tweak these parameters carefully...
Screen stretch with CTRL-A
Copied the stretch from the ScreenTransferFunction process to the HistogramTransformation process and applied it to the integrated image (then reset the Screen Transfer Function)
Saved the file as a Jpg and resized for upload to IIS.

I attached the resized stacked image and a screen shot showing the processes I used. Hope this helps...

As I originally suggested, the only thing you probably missed was doing a screen stretch after the integration. Data out of the camera is in linear form - the values in each pixel are a linear representation of the numbers of photons captured. Our eyes don't work that way. We see light logarithmically and the raw data needs to be stretched. In PixInsight you can do a screen stretch to see what the data looks like with the ScreenTransferFunction process (CTRL-A does an automatic STF on the current image). To make this a permanent stretch you need the HistogramTransformation process.

Cheers,
Rick.

[hobbit]

Thanks for that Rick and thanks for the dot point guide.
Question though is why do they look ok as separate images?

Pete

[RickS]

Pete: when I load the individual subs into PI they look exactly the same as the integration. They all need a screen stretch before you can see any more than the brightest stars. If you're seeing something different I'm not sure why that would be?

Cheers,
Rick.

[LewisM]

A word of caution: I downloaded the files from FileFactory at the link above. I ended up taking over an hour removing a browser redirect hijacker that FileFactory's downloader bundled in (with no opt out or even warning). It takes over your search engine, and pretends to be a search engine, whereas it is a strong hijack/trojan. All my antivirus stuff went crazy, and it took combinations of ADW, Hitman Pro and Malwarebytes to get rid of it, and I still have a background program TRYING (but being blocked by MWB) to launch a new search engine. I forget the trojan name, and the "search engine" is Search Guru" - which bundles with other crap too. All software shows it as a HIGH RISK malware/trojan.

Not saying that Hobbit put it there - not at all - it's part of FileFactory's sneaky underhanded practice. They also bundled and rebundled the zip to be zips within zips. EEK!

[hobbit]

Hi Lewis,
I just tried downloading it myself and got the same file that I uploaded. I scanned it with avast which didn't find any issues.
However just to be safe I have now removed the link.

[LewisM]

I got the file fine, but FileFactory installed their crap through their "donloader". It did not seem to offer me any alternative rather than using their downloader, which was damned stupid of me.

No harm done - but it did drop a LOT of stuff into an otherwise CLEAN system - 37 files in total, all date generated the same day.

Interesting data - the central star 52 Cygni sure dominates it though.

[MrB]

Pretty well known that most of those file host sites are dodgy, but the Filefactory one does atleast give the option of a clean file(non-exe) if you 'opt out' by unchecking the box for their 'download manager'.
Trend Micro has never reported a problem with the files saved with the box unchecked.