Is this "walking noise"?

[Longinthetooth]

Many of my images suffer from what I've been calling "digital rain" because it looks like rain falling on a windy day, slanting diagonally across the view. Is this "walking noise" which can be dealt with by dithering?  Roughly 1.5 hours of 90 second exposures unguided.

[carastro]

Looks like plain noise to me not walking noise, that comes in streaks.

Should disappear the more data you have, also dithering if you can do it.

Carole 

[tomato]

I think there is some slight evidence of walking noise from top left to bottom right?
l have recently used dithering between 60 sec subs and initial indications are that this has removed the walking noise.

Nice image of M33 btw.

[tooth_dr]

It isn't a very strong example of walking noise.  If you can dither then definitely do it.

I removed the colour noise from your image, which helps the overall background I think.  Left side has colour noise reduced.

 

[Longinthetooth]

Thanks, all, for your swift replies. Yes top left to bottom right. I've not got to guiding yet, never mind dithering, but know I have to give it a go! I've been darkening the background to make the pattern less obvious but losing fainter detail in the postprocessing.

Without going "off topic" how do I go about removing "colour noise" please?

JB

[tooth_dr]

2 minutes ago, Longinthetooth said:

Without going "off topic" how do I go about removing "colour noise" please?

JB

PS -> camera raw filter -> move colour noise slider to say 10-15.  Nothing to technical in it but it makes a difference.

[Longinthetooth]

Thanks tooth_dr. I'll give that a try along with the other suggestions above.

 

[ollypenrice]

Have a look at a single sub. You may see the same streaking top left to bottom right. If you do it's inherent to the sensor, I'd have thought. I'd try a large scale dither, at least of 12 pixels. You'll lose a bit around the edges but probably worth it.

I don't have this problem but, if I did, I'd import the image into Photoshop, rotate it till the streaking was vertical or horizontal, then run Noel's Actions on it (Vertical or Horizontal Banding Reduction.) Noel's Actions is the old name but I'm old as well! It's here: https://www.prodigitalsoftware.com/AstronomyToolsActions.html

Olly

[emyliano2000]

34 minutes ago, ollypenrice said:

rotate it till the streaking was vertical or horizontal, then run Noel's Actions on it (Vertical or Horizontal Banding Reduction.)

That's a very good tip, thanks. 

Emil

[Longinthetooth]

Thanks for that Olly.

[Longinthetooth]

Here is a single frame from my stack, stretched and compressed to show here of course. I don't think there's a pattern visible but perhaps others will know better.

Edited January 23, 2020 by Longinthetooth

[ollypenrice]

On 23/01/2020 at 16:59, Longinthetooth said:

Here is a single frame from my stack, stretched and compressed to show here of course. I don't think there's a pattern visible but perhaps others will know better.

That looks OK but how does it stretch?

Olly

[wimvb]

One other test you can do: put the first and last unregistered subs on top of each other and inspect. Is there star drift in the same direction as the streaks in the final image? If so, then it's definitely walking noise. Dithering will help get rid of it.

[Longinthetooth]

32 minutes ago, wimvb said:

One other test you can do: put the first and last unregistered subs on top of each other and inspect. Is there star drift in the same direction as the streaks in the final image? If so, then it's definitely walking noise. Dithering will help get rid of it.

Good idea Wim. Thanks for that.

9 hours ago, ollypenrice said:

That looks OK but how does it stretch?

Olly

Sorry Olly. Could you enlarge on that for me?