Author Topic: Stacking frames of different exposures  (Read 657 times)

Offline Igor

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Stacking frames of different exposures
« on: 2019 October 09 02:52:23 »
Hello,

I wonder how to integrate frames of different exposures, i.e. 600s and 1200s H-Alpha frames ? Does the integration process take the different frame qualities within the noise evaluation processing ?

Thanks for your help.

Regards

Igor

Offline John_Gill

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Re: Stacking frames of different exposures
« Reply #1 on: 2019 October 09 04:40:12 »
Hi,,

I would do the following for each stack of images: ImageCalibration ---> CosmeticCorrection. You will now end up with separate stacks of "clean" images.  Now load all the images into SubFrameSelector to determine the reference/weighting of the images.  (You can output only the "approved" images to a folder). Finally continue with StarAlignment using the reference image from the SFS and add all images (or add just the approved images from SFS) and you are done.


space is not black
John
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline Igor

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Re: Stacking frames of different exposures
« Reply #2 on: 2019 October 09 06:02:56 »
Hi John,

Many thanks.

After CosmeticCorrection, Weighting and Alignment of each frame, I understand that you will mix 600s and 1200s frames into one unique Integration Process  ?

Regards

Igor

Offline John_Gill

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Re: Stacking frames of different exposures
« Reply #3 on: 2019 October 09 23:35:52 »
Correct.  Basically calibrate and clean up all the images per stack (filter/exposure) and then StarAlignment for everything.  This also will work when using images from different scopes/camera FOV.


John
APM 107/700 apo on CGX mount
ZWO Optics - Autoguiding
ZWO1600mm and filters
... when there are no clouds ...

Offline airscottdenning

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Re: Stacking frames of different exposures
« Reply #4 on: 2019 October 10 15:34:36 »
Igor,

The best way to integrate a mix of exposure times depends on what you're trying to do.

A common reason to do this is to achieve higher dynamic range in the integrated image. You want to use the short exposures to avoid overexposing the brightest areas in your image (for example to preserve star colors) AND the long exposures for the dim areas in the same final image (for example to bring out faint nebular details without as much noise).

I don't think you will achieve that optimal mix if you just integrate all the exposures into a single stack.

Rather, you want to use the HDRComposition process. This lets you set thresholds for choosing the dimmer values in the final HDR composite. You first have to prepare all the subs as John suggests, including registering all of them to a common reference. Then you integrate each exposure length into its own stack. And finally you run HDRComposition to combine the resulting stacks.

Hi John,

Many thanks.

After CosmeticCorrection, Weighting and Alignment of each frame, I understand that you will mix 600s and 1200s frames into one unique Integration Process  ?

Regards

Igor

Offline Igor

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  • Posts: 18
Re: Stacking frames of different exposures
« Reply #5 on: 2019 October 10 23:35:59 »
John, Airscottdenning,

Thanks for your help  :)

Regards

Igor