M81-M82 beyond help

[Davey-T]

Took a few subs of M81-M82 while trying to get the focal reducer to fit squarely in the focuser so took it on and off quite a few times without paying too much attention to getting it back in the same spot so produced a lot of higgledepiggldy frames at various angles and eggy stars at various angles.

Just had a go at sticking them all together in PS and the main problem is the terrible background sky (lots of other faults but the sky is worst) I've tried Gradient Exterminator which did a pretty good job considering but wondered if anyone had any ideas to improve it, would one of PIs background tools be any use or is it beyond help ? 

Dave

 

[Mr niall]

You're not happy with that?? I tried taking a picture of the moon through my iPhone and it looked like a broken frisbee on a black tablecloth....

[wimvb]

That doesn't look too bad. What exposure time did you use, and have you used flats?

[Davey-T]

56 minutes ago, wimvb said:

That doesn't look too bad. What exposure time did you use, and have you used flats?

All 600 secs exposures, varying amounts of RGB, lots of luminance, fully calibrated, haven't done much in the way of processing just a bit of linear stretching and saturation and a play with the stars, didn't think it was worth proceeding as the background sky is a mess.

I took some HA as well for M82 but haven't added it yet.

Dave

Heres the stacked L, you can see I didn't bother trying to keep the frame aligned as I was taking the camera and flattener / reducer on and off trying to get round stars.

Had to use Registar to line up LRGB.

 

[wimvb]

Would you mind putting the stacked, but otherwise unprocessed image in dropbox, so we can have a look at it? I'm not at my computer right now, and my mobile screen is too small. But I could have a proper look at your image later this evening.

Cheers,

[Bruce Leeroy]

Aggressive noise reduction with a loss of some data. Using Gimp paint program.

Duplicate layer

Set top layer mode to "Multiply"

Slide opacity of the top layer to reduce the effect  until desired result....76% for your image

The screenshot shows the same method.

[Barry-Wilson]

Hi Dave

I'm certain that PI will be able to handle the aligning, colour calibration, gradients, NR etc.  DBE is a marvellous tool.

Give it a go and come over to the dark side . . .

[wimvb]

Now from my computer, with a much better view of the original image:

The dark space around M81 is most likely due to the ABE process. Try DBE with large samples (35 px if star field allows), few samples (one in each corner, plus 1 - 2 on each edge, a few more to the middle), but make absolutely sure you stay away from anything resembling nebulosity. Placing large samples over stars is allowed (but not recommended), but NEVER over nebulosity, unless you want to kill it. Apply without any correction to get a background model. Depending on what this model looks like, use division or subtraction as correction method and aplly again. The image you get will always be noisier, because DBE (and ABE) remove background signal, but can't remove the noise. SNR is smaller after because S decreased but not N.

Before I apply DBE, I always make sure that ANY stacking edges are cropped. Create a crop area with dynamic crop. Rotate to get the largest image area possible.

Hope this helps.

[Jannis]

to me it looks like the flats didnt work properly, judging by the corners, but i might be wrong. coule something have dewed up causing flats not to work properly maybe?

[Davey-T]

6 hours ago, wimvb said:

Now from my computer, with a much better view of the original image:

The dark space around M81 is most likely due to the ABE process. Try DBE with large samples (35 px if star field allows), few samples (one in each corner, plus 1 - 2 on each edge, a few more to the middle), but make absolutely sure you stay away from anything resembling nebulosity. Placing large samples over stars is allowed (but not recommended), but NEVER over nebulosity, unless you want to kill it. Apply without any correction to get a background model. Depending on what this model looks like, use division or subtraction as correction method and aplly again. The image you get will always be noisier, because DBE (and ABE) remove background signal, but can't remove the noise. SNR is smaller after because S decreased but not N.

Before I apply DBE, I always make sure that ANY stacking edges are cropped. Create a crop area with dynamic crop. Rotate to get the largest image area possible.

Hope this helps.

Using Maxim and P'Shop , used Gradient Xterminator which is probably the cause of the dark space as I wasn't very careful selecting the galaxies and stars, I've uploaded the TIF images to Dropbox, do I need a user name for you to download them ?

Dave

[Davey-T]

7 hours ago, Barry-Wilson said:

Hi Dave

I'm certain that PI will be able to handle the aligning, colour calibration, gradients, NR etc.  DBE is a marvellous tool.

Give it a go and come over to the dark side . . .

More expense 

Dave

[wimvb]

13 minutes ago, Davey-T said:

Using Maxim and P'Shop , used Gradient Xterminator which is probably the cause of the dark space as I wasn't very careful selecting the galaxies and stars, I've uploaded the TIF images to Dropbox, do I need a user name for you to download them ?

Dave

If you share the folder, you can just PM the link, and I should be able to download the data.

[Davey-T]

13 minutes ago, wimvb said:

If you share the folder, you can just PM the link, and I should be able to download the data.

Done that, I think 

Dave

[wimvb]

Here's your image (just the rgb data). Definitely not beyond help, I would say.

(click on the image & the button in the lower left to see the full size version)

Most important process steps:

• Crop
• Aligned the channels in the rgb stacked image
• DBE to remove vignetting (division) and to remove remaining gradients (subtraction)
• Deconvolution & Noise reduction
• Stretch & increased saturation
• HDR compression to increase contrast in M82
• Star reduction

There is still some vignetting left in the lower corners, but I didn't want to clip the background.

[tomato]

Very nicely done, and as you said, the raw data cannot be too shabby either.