Is this vignetting?

[Larry 1969]

Nope... That wasn't it...

Larry

[UlteriorModem]

That will probably do it

Here is my pass at just the single frame completely un-calibrated. There is a good deal of vigenetting in the data made worse by the high levels of sky glow. Neither of which you can do much about. A good set of calibration files will help with that though.

L_0090_ISO800_180s__56F by Tom Whit, on Flickr

[startoolsastro]

Hi,

The issue is most likely failure to remove stacking artifacts. In the image you posted I can see a one pixel high stacking artifact at the top and at the bottom, as well as a one pixel wide stacking artifact to the left and to the right.

For some reason, DSS' intersect mode almost works, but fails to properly crop by just one pixel to the top, bottom, left and right. It's a long standing bug...

If stacking artifacts are not removed not removed (cropped), Wipe will, in turn detect the darker-than-real-background artefacts and will then locally back off, as it doesn't want to clip your signal by subtracting the bias/gradients it found from it. Wipe is - by design - very careful.

From the docs;

Preparing data for the Wipe module

^ Leaving stacking artifacts in will cause Wipe to interpret the anomalous data as true background, causing it to back off near the location of the artifacts.

It is of the utmost importance that Wipe is given the best artefact-free, linear data you can muster.

Because Wipe tries to find the true (darkest) background level, any pixel reading that is mistakenly darker than the true background in your image (for example due to dead pixels on the CCD, or a dust speck on the sensor) will cause Wipe to acquire wrong readings for the background. When this happens, Wipe can be seen to "back off" around the area where the anomalous data was detected, resulting in localised patches where gradient (or light pollution) remnants remain. These can often look like halos. Often dark anomalous data can be found at the very centre of such a halo or remnant.

The reason Wipe backs off is that Wipe (as is the case with most modules in StarTools) refuses to clip your data. Instead Wipe allocates the dynamic range that the dark anomaly needs to display its 'features'. Of course, we don't care about the 'features' of an anomaly and would be happy for Wipe to clip the anomaly if it means the rest of the image will look correct.

Fortunately, there are various ways to help Wipe avoid anomalous data;

• A 'Dark anomaly filter' parameter can be set to filter out smaller dark anomalies, such as dead pixels or small clusters of dead pixels, before passing on the image to Wipe for analysis.
• Larger dark anomalies (such as dust specks on the sensor) can be excluded from analysis by, simply by creating a mask that excludes that particular area (for example by "drawing" a "gap" in the mask using the Lassoo tool in the Mask editor).
• Stacking artefacts can be cropped using the Crop module.

[Larry 1969]

Thanks Ivo!
I think I understand. My first step is AutoDev then Bin 50%.
I guess crop should be my next step instead of wipe.
I will reprocess this and report back.

Larry

[Juno16]

Hi Larry,

Let us know how that works out. I always use Intersection stacking in dss and only see the usual “fringe” stacking artifacts mostly caused by the meridian flip.

[Larry 1969]

Ivo's solution worked!
I was confused with the processing process. I was using the wipe module to bring out the stacking errors then cropping...
I have a better understanding now. Thanks for all the help and patience!

Larry

[Star Dad]

Many times I find going simply to wipe will reveal that large "light border area". Even after I have cropped the image. I finally decided that the best method was to autodev then wipe. See where the light border stands out and cancel the wipe, and then go back and re-crop the image. repeat until that light border are is gone. Usually a simply eyeball approach is all it takes. Hopefully the object you are photographing is in the middle with plenty of space around it to crop. Lately, because my town recently installed 5,000K led street lights I can no longer use a gradient but have to use the Vignetting in Wipe with the dark filter set to 2 pixels. Good luck!