Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Having issues with getting color in M51, did I make a mistake in setting my offset?

  • Please log in to reply
5 replies to this topic

#1 smiller

smiller

    Ranger 4

  • *****
  • topic starter
  • Posts: 328
  • Joined: 27 Oct 2018
  • Loc: Vancouver Washington (not BC!)

Posted 25 June 2022 - 04:18 PM

Hi Folks,

 

A few days ago I had some success in my first deep sky galaxy attempt (M51), using 26 15 second  subs (I'm on an Alt/Az dob so I'm limited to exposures length):

 

FirstWhirlpoolSecondProcessSmall.jpg

 

This was using DeepSkyStacker, Gimp for basic color work/stretch, and I did a tad of Denoising too.  Still learning but I was happy I got some color.

 

However, last night, I tried again to get more integration time.  I did a few minor changes (10 second subs with higher gain) but one big change is I added an offset of 21 (using an ASI485MC camera on a 12" Alt/Az Dob).   I was reading that this was good to ensure he histogram is not pegged to the left, but I think I made a mistake.  Because my stacked image is nearly monochromatic.  I can't seem to get any color out of it other than changing the overall hue.  Here is the result after stacking and a basic stretch and saturation/chromo increase to see if there is color:

 

IMG_8539NewM51 basic stretch.JPG

 

Compare that to my old M51 with just a basic stretch.  Very noisey and crude, but the point is clearly there is color in there:

 

IMG_8549 FirstM51 basic stretch.jpg

 

Here are the comparisons of my settings, both done on very similar nights at about the same time:

 

Setting                     Old              New (no color)

Bit depth                  12                12

Color                        Raw             Raw

Exposure Time         15 secs       10 secs

Total Exposures       26                118

Gain                         195              275

Brightness               1                  21

Sensor Temp           24                22 C

Histogram               0-4095         91-4095

 

My bias and darks matched the gain and brightness of the lights for each respective session, but even if I stack without them, no color on the new one, color on the old one.   So I know it isn't just the offset it the bias/darks that is screwing up the color (but perhaps it's a factor?).

 

What am I doing wrong the second time?   Was setting an offset a big no-no?  I'm fairly certain moving from 15 second subs to 10 seconds isn't it, especially given that I quadrupled the number of subs.  

 

Thanks

 

Steven


Edited by smiller, 25 June 2022 - 04:43 PM.


#2 Oyaji

Oyaji

    Viking 1

  • *****
  • Posts: 583
  • Joined: 05 Sep 2018
  • Loc: Central Illinois, USA

Posted 25 June 2022 - 04:55 PM

I suggest you download the free trial version of Astro Pixel Processor and try it out on your subs.  You know you will eventually end up either with APP or Pixinsight, so you might as well get started!  

 

APP stacks and processes the stacked image, so you don't need DSS separately to stack the subs.

 

APP has a bit of a learning curve, but it has a powerful routine that gets the color right by evaluating the stars in your stacked image and comparing their colors to the known colors of stars in the Milky Way.  (You would probably want to exclude M51 itself from the stars being evaluated).

 

If in APP you get an image without color, then you may have to force it to debayer (this is done at the very first stage-- the "0 RAW/FITS" tab at the left). 

 

And it isn't all that expensive to buy the program after the trial. You can rent it for 60 Euros per year or buy it outright for 165 Euros.   Right now the exchange rate is $1.06 per Euro, the lowest in many years.  

 

Oh yes, I wouldn't think that the modest offset you have chosen would kill the color.  

 

P.S.  Your initial image was pretty darned good--imaging with Dobs is not for the faint of heart!  


Edited by Oyaji, 25 June 2022 - 05:03 PM.

  • smiller likes this

#3 smiller

smiller

    Ranger 4

  • *****
  • topic starter
  • Posts: 328
  • Joined: 27 Oct 2018
  • Loc: Vancouver Washington (not BC!)

Posted 25 June 2022 - 05:13 PM

I suggest you download the free trial version of Astro Pixel Processor and try it out on your subs.  You know you will eventually end up either with APP or Pixinsight, so you might as well get started!  

 

APP stacks and processes the stacked image, so you don't need DSS separately to stack the subs.

 

APP has a bit of a learning curve, but it has a powerful routine that gets the color right by evaluating the stars in your stacked image and comparing their colors to the known colors of stars in the Milky Way.  (You would probably want to exclude M51 itself from the stars being evaluated).

 

If in APP you get an image without color, then you may have to force it to debayer (this is done at the very first stage-- the "0 RAW/FITS" tab at the left). 

 

And it isn't all that expensive to buy the program after the trial. You can rent it for 60 Euros per year or buy it outright for 165 Euros.   Right now the exchange rate is $1.06 per Euro, the lowest in many years.  

 

Oh yes, I wouldn't think that the modest offset you have chosen would kill the color.  

 

P.S.  Your initial image was pretty darned good--imaging with Dobs is not for the faint of heart!  

I'm happy to buy the right tools.  I'm not sure I want to jump right into Pixinsight yet (it does seem daunting and I'm taking it one step at a time, especially since I'm also doing planetary, solar, and lunar on this scope, so lot's of different tools and techniques to learn in such a short time!).   I'll give APP a try!   I'm just looking for that logical "next step" as I slow climb that long ladder...


Edited by smiller, 25 June 2022 - 05:56 PM.


#4 Astronomiser

Astronomiser

    Vostok 1

  • *****
  • Posts: 137
  • Joined: 13 Jan 2008
  • Loc: Oklahoma

Posted 25 June 2022 - 05:51 PM

I would download Sharpcap, and that way you can stack live while Imaging.  You can adjust offset also in test runs to see what impact it has.  Sharpcap is so cheap, it is a insignificant cost.

 

Several folks broadcasting on NightSkiesNetwork.com use Alt/Az with nice results.  Usually 8-12 sec. range.

 

Gary


  • smiller likes this

#5 southernharry

southernharry

    Explorer 1

  • *****
  • Posts: 61
  • Joined: 12 Dec 2020
  • Loc: Woodstock, GA

Posted 25 June 2022 - 06:43 PM

APP changed my life - highly recommend it.  I also use Affinity Photo for some touchup.


  • Oyaji likes this

#6 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 29,366
  • Joined: 27 Oct 2014

Posted 25 June 2022 - 06:57 PM

Hi Folks,

 

A few days ago I had some success in my first deep sky galaxy attempt (M51), using 26 15 second  subs (I'm on an Alt/Az dob so I'm limited to exposures length):

 

attachicon.gifFirstWhirlpoolSecondProcessSmall.jpg

 

This was using DeepSkyStacker, Gimp for basic color work/stretch, and I did a tad of Denoising too.  Still learning but I was happy I got some color.

 

However, last night, I tried again to get more integration time.  I did a few minor changes (10 second subs with higher gain) but one big change is I added an offset of 21 (using an ASI485MC camera on a 12" Alt/Az Dob).   I was reading that this was good to ensure he histogram is not pegged to the left, but I think I made a mistake.  Because my stacked image is nearly monochromatic.  I can't seem to get any color out of it other than changing the overall hue.  Here is the result after stacking and a basic stretch and saturation/chromo increase to see if there is color:

 

attachicon.gifIMG_8539NewM51 basic stretch.JPG

 

Compare that to my old M51 with just a basic stretch.  Very noisey and crude, but the point is clearly there is color in there:

 

attachicon.gifIMG_8549 FirstM51 basic stretch.jpg

 

Here are the comparisons of my settings, both done on very similar nights at about the same time:

 

Setting                     Old              New (no color)

Bit depth                  12                12

Color                        Raw             Raw

Exposure Time         15 secs       10 secs

Total Exposures       26                118

Gain                         195              275

Brightness               1                  21

Sensor Temp           24                22 C

Histogram               0-4095         91-4095

 

My bias and darks matched the gain and brightness of the lights for each respective session, but even if I stack without them, no color on the new one, color on the old one.   So I know it isn't just the offset it the bias/darks that is screwing up the color (but perhaps it's a factor?).

 

What am I doing wrong the second time?   Was setting an offset a big no-no?  I'm fairly certain moving from 15 second subs to 10 seconds isn't it, especially given that I quadrupled the number of subs.  

 

Thanks

 

Steven

You can't lose color by adding an offset (which is basically required standard practice).  Something else is going on here.


  • smiller likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics