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Red noise in background

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#1 shawnhar

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Posted 07 March 2013 - 09:31 AM

I feel like that kid in The Shining every time I stretch my images and I want to scream murder....
So what gives, I see other folks get it too.
DSLR subs, doesn't seem to matter if it's Winter or Summer, still get it. My last pic had it in diagonal bands.
Is this a darks issue? not enough? Wrong setting in stacking in DSS?

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#2 CounterWeight

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Posted 07 March 2013 - 11:04 AM

Have you tried using your software to split the color panes into R / G / B and compare the backgrounds ? I do very little RGB because of my horiffic LP but when I do, I always split the colors apart using CS or PSP and examine. You have to be careful though in any manipulations as the finel image when you reassemble may need additional color balancing. I've also played with reducing the saturation and brightness on that background with a very narrow fuzzy factor, which casts it more to a grey look. Lots of approaches, but it depends on the software. I'd just add too that it's important get accurate level you want to preserve in the low contrast detail and try to keep a margin between that and what you are manipluating so it wont intrude into the object, some do this with layering and masks or the lasoo tool and use feathering to keep the blend area from rapid contrast transitions...

#3 SMigol

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Posted 07 March 2013 - 12:33 PM

The diagonal bands tends to show up when the darks are not the same temperature of the lights. If you are checking EXIF temperatures of each, try to match to within 1C.

I also see red in my shots taken in the light polluted back yard. I know a lot of this has to do with the sodium vapor streetlight nearby. Thus, I try to get out of town if I can. I assume that you are using some light suppression filter? I'm using the IDAS LPS filter on my DSLR.

In processing I'm doing something similar as what Jim says. In PI I create a luminance mask and use that to toggle NR between the background and foreground. I also use this mask to drive the saturation of the weakest parts of the signal down which gives some artificial greyness to the muddy dark parts of the sky.

This does sacrifice any background galaxies and stars that otherwise would be visible.

#4 CounterWeight

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Posted 07 March 2013 - 12:55 PM

Another thing I forgot to mention the doing a selection in the adjustment layer / invert and blur with a reasonable anount of feathering - this accomplished differnt ways if using lasoo tool or layer masking.

Depending on the software always check if an automated operation converts bitdepth down to 8 bit, and increase depth back to 16 after the action or filter or function applied (I just mention as I constantly forget about this)

Something to consider or be aware of is where in your workflow you do things - the things I mention are maybe better done after any initial adjustments or manipluations of levels/curves or contrast or 'highligh/midtone/shadow', shaprpening/unsharp mask, and before any final smoothing or smoothing based noise redution.

The issue of doing things out of order is there will be obvious color gradient steps with obvious edge gradients or color banding(vs. smooth transitions) and 'blobs'(my technical term) in darker areas. IMO it's more an issue of visually than absolute values, things don't need to be eliminated entirely, just to where they dont matter or intrude?

#5 shawnhar

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Posted 07 March 2013 - 02:37 PM

Thanks! I have not tried to to split the rgb into individual color panes, will have to try that and the tips you gave Jim, thanks for your help.
My camera is the Conon XS, I don't think it has exif data, but I don't use any filters and have pretty harsh skyglow, that would explain the recent increase in red, as I have been shooting lower targets to the North East, where my strongest light pollution is. I now realize the targets with less of the red were shot higher in the sky. I can't guide so a filter is out of the question since 1:00 is my max reliable sub.

#6 Footbag

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Posted 07 March 2013 - 02:50 PM

Thanks! I have not tried to to split the rgb into individual color panes, will have to try that and the tips you gave Jim, thanks for your help.
My camera is the Conon XS, I don't think it has exif data, but I don't use any filters and have pretty harsh skyglow, that would explain the recent increase in red, as I have been shooting lower targets to the North East, where my strongest light pollution is. I now realize the targets with less of the red were shot higher in the sky. I can't guide so a filter is out of the question since 1:00 is my max reliable sub.



All cameras have EXIF.

#7 shawnhar

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Posted 07 March 2013 - 04:59 PM

Indeed and it turns out the lights were 8c and the 1st dark was 3c on the the ones that caused the diagonal banding.
Another piece of the puzzle solved, thanks.

#8 shawnhar

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Posted 07 March 2013 - 07:15 PM

Holy *BLEEP* none of my darks match!
http://sourceforge.n...ects/darkmaster

#9 proteus5

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Posted 07 March 2013 - 09:59 PM

Shawn,

In the image you posted I don't see the red or the banding. A thought occurred to me about screen resolution. I run my monitor at 1280x1024. I changed it to 1024x768 and I begin to see a little of it, but not much. I have the same problem as you with the red, and also getting go color balance. My question, am I using to high a monitor resoution when I do my post processing or does it not matter.

Oh and thanks for the link to darkmaster, going to have to try that as like you my darks are off also.

#10 shawnhar

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Posted 07 March 2013 - 10:16 PM

Robert I run my res the same, maybe I didn't stretch the image enough to really show it in the 1st post. Looking at my dark temps I am not even within 10 degrees on any of my attempts the last 2 months

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#11 CounterWeight

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Posted 07 March 2013 - 10:26 PM

I've not had an issue with this sort of thing since I went to regulated cooling. My first CCD was the Orion SSPv1 and I had some odd artifacts as it too was unregulated.

#12 proteus5

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Posted 07 March 2013 - 10:49 PM

I can see it now, looks just like mine. I tried dithering for the first time in my M51 image and it seemed to be less. Don't know if that was the reason or not.






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