I seem to be hopeless with image processing. I have Photoshop and Nebulosity, and DSS. I stack with DSS, always with dark frames and offset/bias frames (rarely use flats). I shoot exclusively at ISO800, with a Canon 450D DSLR. My scope is a 10" light weight imaging newt with guidescope. I use Metaguide to manage my ASI120MM guidecamera. It sits on a NEQ6 on a pier in my observatory. My sub times are usually between three and five minutes, and they always look great on the camera screen or on BYEOS.
My problem emerges when I move into Photoshop or Nebulosity. My stacked images generally look like S*** when opened in these apps. I have done plenty of reading and research but never seem to achieve the results I see displayed in posts here.
What am I doing wrong? Why does a stacked image look not much better than a single sub?
I have uploaded a FIT file to Astrobin (M83). Can someone have a go at processing this and give me some feedback? The file was made up of 22 subs of 4 min 35 sec each, with darks and offset/bias (no flats).
So here is the Astrobin public area posted jpeg in my sharing folder:
I think you have to subscribe to the Astrobin Raw Data feature (which is free for up to 500mb), in order to access it but I could be wrong. I just joined myself.
I think your problem lies in DSS, not post processing. For a start the JPEG is very dim considering the size of scope, and long integration time. A few
30 second subs with my 8" would result in a much brighter image than that.
Are you full bottle on DSS? It does have a fairly comprehensive user
guide in the help tab. The image, although dim, actually looks pretty good.
raymo
'
Hi Glen, This is the best I could do. The image was very dark, so I've had to overdo things a bit to get the galaxy to stand out, and I've had to
darken the sky a bit too much for the same reason.
Somebody much more experienced than me could no doubt do better.
cheers raymo
Last edited by raymo; 26-03-2015 at 10:56 PM.
Reason: missing word
Glen, only Astrobin users that you specifically invite (individually, by name) can see your private shared folder. If you want anyone to be able to access that folder you need to add it to the public data pool. To do this, go to your raw data library, then "select" the file, and using the "share" button, share to the public data pool.
if you just want to "invite" specific users to access your private shared folder, I am keen to have a crack at your FIT file. go to the private shared folder, and then from the Actions button click "invite". my astrobin username is rmuhlack
Hi Glen
I cant access your Fit getting a 404 error.
I think that i live in your general area perhaps we could catch up sometime.
I'm still learning the ropes my self but i think we could learn a few things from each other.
Glen. If you are applying a bias frame to your darks and/or lights, you have most likely truncated your data. Your experience and image tends to indicate as much.
Basically, I now avoid 16bit processing methodologies with DSLR data - it's not linear.
Suggest you try the following;
1. Stack your darks as is, with no pixel rejection
2. If you had flats for this image take bias frames and stack same as darks.
3. Again, if you had flats - calibrate with master bias
4. Calibrate your light subs with your master dark and master flat (if you had one) only - the bias is in the dark.
I have found processing in this manner consistently reliable, maximizing the available data. It manages the non-linearity caused by in-camera processing of RAW data, which is unavoidable.
Good flats make a difference. If you get around to taking flats, and you really should, pixel rejection is necessary as a rule. The typical method of combination is average/multiplicative using a Sigma pixel rejection. PixInsight terminology, but you get the drift.
A starting place... you may be able to improve on the process.
Rowland you make some good points and they probably explain why my individual subs look so bright and dynamic and the stacked end produce looks dull and dark. I do use bias frames, darks, and occassionally flats, but I hear so much conflicting opinions on this. I accept there is probably one technique for DSLRs (Canons), and another for CCD camera image processing. My setup/preferences in DSS may also be part of the problem. I still have no idea which of the stacker apps is the best choice for my images, they all seem to have their fans.
1. You've got some streaking in the background which is typical of mismatched temperature between darks and lights. I have processed the background to be darker than I normally would to hide this.
2. Focus is also a little off, so that is something to look at for future sessions. I use a Bahtinov Mask and Bahtinov Grabber software. By using this in combination with BYE, it reports the focus error in microns, and will tell you when you have achieved "focus" for your telescope/camera combo. I find this to be a quick and reliable means of achieving good focus out in the field. I have used some star reduction in processing to compensate for the star bloat due to focus.
flats would iron out the background and make it much easier to process. I wish I had started doing them earlier - they are easy with a DSLR too, set to AV (canon) at twilight and snap away.
Glen. AstroArt is the easiest to setup as described. But Nebulosity or Pixinsight will do, just as well. Not sure about DSS, you may need several steps - but it's worth it. The trial version of AstroArt is a good way to practise. Despite the watermark, as I recall.
I seem to be hopeless with image processing. I have Photoshop and Nebulosity, and DSS. I stack with DSS, always with dark frames and offset/bias frames (rarely use flats). I shoot exclusively at ISO800, with a Canon 450D DSLR. My scope is a 10" light weight imaging newt with guidescope. I use Metaguide to manage my ASI120MM guidecamera. It sits on a NEQ6 on a pier in my observatory. My sub times are usually between three and five minutes, and they always look great on the camera screen or on BYEOS.
My problem emerges when I move into Photoshop or Nebulosity.
Glen I can't emphasise enough the importance of taking flats.
You really need to apply them to get the best results out of your gear.
I don't bother with offset/bias frames because they're not needed IMO.
When I image I guide using PHD and stack my frames using DSS.
I don't adjust anything in DSS once it spits out the image, I move it straight through to Photoshop and do all my adjusting there.
All the Deep Space images I've taken (see some my signature) have been taken with a DSLR and processed as above.
I had a quick go at your image but it's difficult to get anything worthy out of a jpg, this is the best I could do (crop) just quickly.
Thanks for that advice RB. I do have the RAW file (as FIT) in the gallery at Astrobin for people that would like to have a go at bringing it out. If your a member of Astrobin I can send you an invite to the file - just give me your user-name.
Thanks for that advice RB. I do have the RAW file (as FIT) in the gallery at Astrobin for people that would like to have a go at bringing it out. If your a member of Astrobin I can send you an invite to the file - just give me your user-name.
Sorry Glen, I'm not a member.
But I've been following your progress from when you joined.
You need to get some processing skills built up because you've got everything else in place and have made great progress with your mod projects etc.
I wouldn't move from a DSLR until you get some processing skills under your belt.
You've probably got the books or read up on the web how to process.
Just need some practice, then you'll rock with the gear and observatory you have.
