Difficulty using DeepSkyStacker - images greyed/washed out after stacking

[Iasus]

Hi all

Newbie to deep sky imaging here, having issues using DeepSkyStacker.

I have some images of the Ring Nebula which I'm using to learn stacking. They are RAW .CR2 format, taken using a Canon 600D DSLR which has been astro-modified. The lights are not brilliant - big vignette due to moon, but I'm not bothered by that as I'm just trying to learn tools atm rather than make "good" images. I also have some images taken with a UHC filter which do not have the vignette anywhere like as bad but they suffer from the same problem described below.

Imgur link shows reference images from my machine for this post: https://imgur.com/a/4ZbL4x3 including before/after stacking and the settings I'm using.

My issue is this:

On loading the light frames into DSS they look fine in terms of colour, DSS shows them as "Gray 16 bit" and correctly IDs the camera.

I then stack them using the lights and darks, and the result is very greyed out, with little to no colour. This happens even with the images taken with the UHC filter which have little vignette, and with other objects.

I've had a google around and other people seem to be having this problem as well. I've tried changing the Bayer settings under "FITS/DDP settings" but it doesn't seem to help.

Can anyone offer any advice or alternative software I could use? I'd like to get DSS working as it seems pretty straightforward, but I have no idea why it's trashing the colour in my images.

Thanks

 

[AstroMuni]

33 minutes ago, Iasus said:

Can anyone offer any advice or alternative software I could use?

I use Siril. Its free and the tutorial is here https://siril.org/tutorials/tuto-scripts/ . Others who are users of DSS maybe able to help fix the problem.

[Rallemikken]

I also shoot with a modded 600D, and stack both in DSS and Siril. Never had issues like you, must be a weird setting.

First: DSS (and Sequator as well) present the finished stacked image in an other way than Siril. Flat and colorless, as Siril seldom shows more than a black square. Load the Autosave.tif/fits into Siril, and play with the preview options (Autostretch and Histogram stretch). There may be more in it than what is immidiate visible.

Second: When shooting with a modded camera, you will need the color calibration routines in Siril, at least it willl save you some work. I always start a stretch with the photometric color calibration in Siril. Than I do a couple of very carefully Asinh-stretches, before I finish in Gimp.

Some times DSS does the best stack, other times it's Siril. I even have had targets that stacks best in Sequator. It's all about learning how to set the options, and as Siril gives you best control, I slowly improves my skills in Siril, and it's the stacking software I use most nowadays. Not the easiest to learn, but not impossible either.

[Felias]

+1 for Siril and its photometric colour calibration, it's very useful. But you should still be able to get a decent stack in DSS... are you using flats at all? They are essential.

[Iasus]

Thanks for the advice guys.

I'll take a look at SIRIL.

Ias

[alacant]

On 15/08/2022 at 16:07, Iasus said:

stack them using the lights and darks

Hi

600d, so lose the dark frames. Instead, simply subtract a constant bias value and use flat frames.

+1 for doing this in Siril. Download here. 

Cheers and HTH.

[Iasus]

5 hours ago, alacant said:

Hi

600d, so lose the dark frames. Instead, simply subtract a constant bias value and use flat frames.

+1 for doing this in Siril. Download here. 

Cheers and HTH.

Hi 

How do I determine the bias value to remove?   Bias frames?

Thanks

Ias

[alacant]

4 minutes ago, Iasus said:

determine the bias value

You can scan a frame taken in darkness at 1/4000s in the siril window: hover -> statistics. Average the pixel values to the nearest power of 2.

You'll find that the offset on a 600d is 2048.

No need for bias frames themselves. But try for your self of course and do post if you see any difference.

Cheers and HTH

[Malpi12]

On 15/08/2022 at 15:07, Iasus said:

DSS shows them as "Gray 16 bit" and correctly IDs the camera.

Hi, I am still trying to get my head round the Imgur page (it is asking me to take more cookies and whitelist my adblocker ! (neither of which I wish to do on this browser )
However a quick look and I have got your settings image off it (dont you just hate message boxes in programs that dont let one copy/paste !)  and examined in IrfanView, see lower down :-

Firstly - I am still a beginner imager with a 60D (astromod) which is similar to the 600d and, after a steep learning curve with DSS, a long time ago, I do get colour ! I was surprised to see "Gray 16 bit " Ah ! I thought !! but it tuned out to be a red-herring and mine also says that ha ! so I have learned something thanks  

So then I compared your settings (on the right below) with mine which (after I removed my bias frames and allowing that I am using Kappa-Sigma clip) looked similar to yours except for the Red Arrowed bits.
I wonder if that may be a cause ?

Edited August 17, 2022 by Malpi12

[Malpi12]

6 hours ago, alacant said:

600d, so lose the dark frames. Instead, simply subtract a constant bias value and use flat frames.

+1 for doing this in Siril.  

Do you know if I can I do that somewhere in DSS as well ?
I did try Siril some time ago but it made my brain hurt and fall off its step learning curve
thanks.

 

Edited August 17, 2022 by Malpi12

[dph1nm]

The washed out DSS image is perfectly normal and correct.  If you put a faint object such as a nebula or galaxy on top of a bright sky then the intrinsic colour of the object will not be obvious. You need to post-process the image to remove the sky, and maybe up the colour saturation. The DSS image settings can do this, but you will have more control in dedicated photo-editing software.

NigelM