StarTools

Hi everyone,

I took some images of the Horsehead nebula the other night and I've started to look into processing them. Unfortunately I've run into a roadblock in the form of the following artifact. This is immediately after autodeveloping, wiping (gradient), and then developing only.
Notice how there's a rectangular area in the center of the frame with the massive gradients on the edges? I'm wondering if I could get some help with processing this away.

Here's the exposure information:

Camera: Canon T3
Lights: 360x 30 second ISO 1600
Darks: 30x 30 second ISO 1600
Bias: 100x ISO 1600
Flats: 50x 1/40 second ISO 1600
Imaging was unguided.
Stacking was done using the Median Kappa Sigma method (for Lights) in DSS.

Here's the stacked image from DSS.

Alternatively, if there's something I can do within DSS that would improve my situation (different Light processing algorithm, something else?), please let me know! I'd also be curious to know why this happens if anyone can shed insight.

Thanks!

Ive had this before ,make sure you dont align data in Dss ,choose bottom left button once startools loads ,linear was not bayered not sure what the actual cause is i`m sure someone will know.

Got it. What do you mean don't align data in Dss?

What you're seeing is caused by stacking artifacts (they're not stacking artifacts themselves).

This section of the manual/website should explain what's happening and how you can avoid it.

Specifically;

Preparing data for the Wipe module

It is of the utmost importance that Wipe is given the best artefact-free, linear data you can muster.
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.
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.
Halo around a simulated dust speck dark anomaly.
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.

Masking out the dust speck in order to make Wipe ignore that location.
Fortunately, there are various ways to help Wipe avoid anomalous data;
The result of making Wipe ignore the anomalous data. No halo-like remnant is left.

• A "dark anomaly filter" parameter can be set to filter out smaller dark anomalies, such as dead pixels or small clusters of dead pixels.
• Larger dark anomalies (such as dust specks on the sensor) can be excluded from the image that Wipe samples 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.

Arrowstar wrote:Got it. What do you mean don't align data in Dss?

when you save picture to file in DSS as a fits you will see bottom left in box two options, choose dont apply adjustments to image.If you choose apply adjustments then the colour wont come out right believe me lols .