LGRB request to Crop - systematic request?

[alcor]

When loading an LGRB I have a systematic request to crop the image to avoid artifacts. However, the images was already cropped during preparation and I cannot see any remaining artifact. Is the request systematic or is it based on some analysis if the border ? In the later case, could ST provide some feedback on the area it found problematic (automask, border size or so one?)
-- thanks - alcor

[admin]

When loading an LGRB I have a systematic request to crop the image to avoid artifacts. However, the images was already cropped during preparation and I cannot see any remaining artifact. Is the request systematic or is it based on some analysis if the border ? In the later case, could ST provide some feedback on the area it found problematic (automask, border size or so one?)
-- thanks - alcor

Hi Alcor,

Yes, the stacking artifacts warning is based on some analysis of the image. It tries to detect large rectangular features close to the borders of the image that vary in brightness considerably. The algorithm used is a bit 'hit and miss' though. The same algorithm is used in the Crop module when you click the StArt, so you can see what StarTools is blabbering on about there

Do let me know if this keeps happening. This feature is probably due for an overhaul...

Clear skies!

[alcor]

Thanks,
After some investigation I found some cause of confusion.

If I load an image (L of LRGB or Open image) and then keep it, I am told that there are artifacts. If I then immediately do a crop and press StArt (I was really wondering what this button was for), it proposes to cut the bottom border (which is indeed slightly darker also this is not visible on the linear image). This is reasonably correct, except that I do not see what I am doing at all on the linear image.

If I load the image as above, keep it, get the message and then do some stretching (just an AutoDev on the whole image), I do see that the bottom is slightly darker (not obvious but visible). But then if I do a Crop, StArt tells me that it does not find any problem ....

I suppose that, if the warning was generated on the linear image, StaRt should also find the the area to remove in the linear image (or maybe it should have been saved with the image, or a warning that if there is none we should go back the to linear image, or whatever to be consistent....). If this may be helpfull I can send you the image causing this problem.

Otherwise thanks for StarTools, very interesting, but I am just learning it.
-- alcor

[ChrisLX200]

The problem I have with this process is that when processing the component stacks of multi-channel images then they all need to be cropped to the same dimensions prior to registering and compositing, so generally I crop 20pixels off all sides regardless of whether that is optimal or not, or if artifacts are worse than usual (usually after removing and replacing the camera and not getting the rotation just right) then crop by 50pixels. However I find it tiresome having to drag the sliders (followed by much clicking!) to get the borders set correctly. Yes, I know if I load a second image stack without closing StarTools in between then it will remember the previous crop dimensions but often I will capture and process a single channel in a night.

I would certainly appreciate some more options in the crop tool, perhaps crop all borders by (n) pixels, or even the ability to type numbers in rather than drag & click sliders.

ChrisH

[admin]

The problem I have with this process is that when processing the component stacks of multi-channel images then they all need to be cropped to the same dimensions prior to registering and compositing, so generally I crop 20pixels off all sides regardless of whether that is optimal or not, or if artifacts are worse than usual (usually after removing and replacing the camera and not getting the rotation just right) then crop by 50pixels. However I find it tiresome having to drag the sliders (followed by much clicking!) to get the borders set correctly. Yes, I know if I load a second image stack without closing StarTools in between then it will remember the previous crop dimensions but often I will capture and process a single channel in a night.

I would certainly appreciate some more options in the crop tool, perhaps crop all borders by (n) pixels, or even the ability to type numbers in rather than drag & click sliders.

ChrisH

I hear you, though I'm not entirely sure why you'd process channels as you acquire them... Wouldn't you want the flexibility of creating a synthetic luminance (for example) and knowing what the colours look like?
Also, wouldn't using a reference frame while stacking solve the problem of having stacking artifacts to begin with?
What sort of stacking solution do you use?

StarTools - for the time being - is a post-processing application and dealing with stacking artifacts and alignment issues is a little beyond the scope of this purpose.