Help with comet integration subtraction?

[fredvanner]

OK. What, exactly did you do to generate the "subtracted" image? Since the background level of the comet image is more than 20 times the background of the star-aligned image, it is clear that you could not just subtract the comet image.

 

[bnickeson]

I'll take you through the steps I performed.

• Calibrated all images and registered them to the star field. So if you ran Blink through the images you'd see the comet moving.
• Then ran all those images through CometAlignment. This produced a series of images in which the comet was aligned. So if you ran them through Blink the comet would appear stationary.
• Integrated all of those comet-aligned images into a comet master with a strong rejection algorithm, thus producing the starless integrated comet master file that you see. Yes, this produced an image that was 20 times the pixel level of the individual subs. I used my typical integration settings (other than the strong rejection), so I'm not sure if that is correct or not but it seems reasonable. I then made some minor cloning adjustments to remove any residual star streaks.
• To create a stars-only image, I went back to CometAlignment and added the star registered images from the first bullet point (I also tried this with the comet aligned subs with no change in results). This time I selected the integrated Comet master as the subtraction operand, with LinearFit and Normalize selected.

All of the files I get from this process result in images that look exactly the same as the input files, i.e. with the comet still remaining. Those are the two images in the folder I uploaded that look virtually identical. As far as I can tell, the process I'm following is exactly the method laid out by RBA and Warren Keller in their books. I've even done this comet method several years ago and I don't remember having an issue with it then.

I've got to be messing something up very basic but I can't figure out what it is.

 

[bnickeson]

FYI, someone on another forum found the solution. When the integration of the comet-only image was done, the Normalization setting was still Additive with scaling, is is common with light frames. However, it looks like in order to properly subtract the comet from the star frames, the Normalization setting must be No Normalization to keep the images at the same pixel levels.

 

[Robert Q. Kimball]

I have a suggestion you might try. On a copy of your comet, use Annodate to place a large "O" around the nucleous of the comet. I think I use a 200 point "O". Then do your comet subtraction. The "O" should show up on the resulting star subs in the right positions. This well tell you whether the comet is being subtracted from each sub.

It took me four days of playing around until I got this: https://www.astrobin.com/at2lro/

 

[Jasonwait]

Sadly I've reached a similar point and have not been able to adequately subtract the comet only integration from the aligned subframes. When the comet isn't perfectly aligned on one of the target frames, it will subtract the comet and the result will look like Marco's images above - I am stuck here. Adjusting the comet position manually is frustrating - adjusting one single X or Y parameter on the first frame will actually also adjust the location of the subtracted comet on the final target frame, even if the final target frame position is left unchanged. I'm not exactly sure how the alignment works, but manually inputting the coordinates precisely is not producing what I would expect to be the correct result. Will upload post an image when I get home..

 

[Jasonwait]

Sadly I've reached a similar point and have not been able to adequately subtract the comet only integration from the aligned subframes. When the comet isn't perfectly aligned on one of the target frames, it will subtract the comet and the result will look like Marco's images above - I am stuck here. Adjusting the comet position manually is frustrating - adjusting one single X or Y parameter on the first frame will actually also adjust the location of the subtracted comet on the final target frame, even if the final target frame position is left unchanged. I'm not exactly sure how the alignment works, but manually inputting the coordinates precisely is not producing what I would expect to be the correct result. Will upload post an image when I get home..

in the images on the left, you can see one attempt at subtracting the comet - the top left frame is the first in the series, and bottom left is last in the series. They are registered to the first image in series, as is the comet only operand. The second set (right hand side) shows the next attempt, after manually adjusting only X and Y parameters for the last image in the series in the CometAlignment process window. The comet was well aligned in the top left image, first in series, and became less well aligned in the second set, top right image, even though no changes were made to the X or Y position of the comet in the first image. Any thoughts?