From: Alan Friedman <alan@greatarrow.com>

Date: April 13, 2008 7:26:06 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Lines of Saturn

Hi Phil,

That is a nasty example of a common problem that results from stacking dim and noisy frames (pretty much the norm for saturn data shot with a monochrome camera and color filters). I've uploaded a couple of stacks from a recent saturn session - about 280 frames were averaged. The stacks were processed in Astro IIDC and then quickly opened in Photoshop to apply an auto levels adjustment. The banding can be seen, though not as serious, and you can see that it is subdued further by using a longer shutter to produce a higher S/N sample in the individual frames. Milton can probably speak with more knowledge on this, but I assume that the stacking is picking up the linearity from the noise pattern in the image.

Are you using the gaussian blur option for frame selection and alignment - and also using a low tolerance for pixel matching? I find both settings are very helpful when the data is noisy and the light levels low.

Hope that you can pull some good results from this session - it looks like the seeing was good.

best regards,Alan

On Apr 13, 2008, at 8:54 PM, Phil Houston wrote:

Milton,

Do you have any idea what could produce the diagonal lines in the
image of Saturn? (link below) I have noticed this effect every so
often in the past but last night, when seeing was good, most of the
longer video captures (2000 frames) produced this effect when stacked
and processed. I have not changed my processing techniques and some
images do not have the lines. I've exaggerated the sharpening to
show the lines more clearly in the linked image and the capture
settings are listed below.

=================== File:20080412_231531_L.mov #frames 1936
Monochrome Camera = Model:'DMx 31AF03' Serial Number:
Camera Display Format: 1024x768 8bit
CCD Image Left: 0
CCD Image Top: 0
CCD Image Width: 1024
CCD Image: Height 768
Gamma: 1.17
Brightness: 951
Black Point: 0
Exposure: 66.67 ms
Sharpness Limiting On: 0
Dark Frame Subtraction On: 0
Flat Frame Correction On: 0
Invert Image On: 0
Flip Horizontal On: 0
Flip Vertical On: 0
Histogram Expand On: 0
Binning Off Monochrome

http://www.knology.net/~pkh111/saturn%20lines.jpg

I am at a loss as to the cause of this noise and would appreciate any
ideas.

Thanks,

Phil