Multi exposure blending

[Anthonyexmouth]

Ok, so i've got about 13ish hours of mixed exposure on M31. 60s,120s,180s and 300. Whats the best way to combine to get the most out of it?

 

Here are the stacks if anyone wants a play.

 masterLight_BIN-1_4144x2822_EXPOSURE-300.00s_FILTER-NoFilter_RGB_(1)_autocrop.xisf

masterLight_BIN-1_4144x2822_EXPOSURE-180.00s_FILTER-NoFilter_RGB_autocrop.xisf

masterLight_BIN-1_4144x2822_EXPOSURE-120.00s_FILTER-NoFilter_RGB_autocrop.xisf

masterLight_BIN-1_4144x2822_EXPOSURE-60.00s_FILTER-NoFilter_RGB_(1)_autocrop.xisf

masterLight_BIN-1_4144x2822_EXPOSURE-60.00s_FILTER-NoFilter_RGB_(1)_autocrop.xisf

Edited February 8, 2023 by Anthonyexmouth

[Budgie1]

I'm not in front of my PixInsight PC at the moment, so details may not be completely correct.

1. Use PixelMath to add the images together is the basic way to combine them all. Although it's a bit rough & ready. 

2. Use the Image Integration tool in PI. I think you'll need to make sure all the images are star aligned (and maybe cropped) for this but I think it gives a better result than PixelMath.

3. Restack all the subs using WBPP but use either a common filename (the proper name of this escapes me just now) or change the exposure limit setting to something like 300, so it stacks all of them into one master, instead of dividing them into individual masters based on the exposure length. 

Hopefully others will help to clarify the above in more detail.  

[Anthonyexmouth]

3 minutes ago, Budgie1 said:

I'm not in front of my PixInsight PC at the moment, so details may not be completely correct.

1. Use PixelMath to add the images together is the basic way to combine them all. Although it's a bit rough & ready. 

2. Use the Image Integration tool in PI. I think you'll need to make sure all the images are star aligned (and maybe cropped) for this but I think it gives a better result than PixelMath.

3. Restack all the subs using WBPP but use either a common filename (the proper name of this escapes me just now) or change the exposure limit setting to something like 300, so it stacks all of them into one master, instead of dividing them into individual masters based on the exposure length. 

Hopefully others will help to clarify the above in more detail.  

Ah yeah, exposure limit. I did use WBPP for all of them but it spat out 4 copies. I'll try again. Will that help with core detail? 

[Budgie1]

2 minutes ago, Anthonyexmouth said:

Ah yeah, exposure limit. I did use WBPP for all of them but it spat out 4 copies. I'll try again. Will that help with core detail? 

Hopefully it'll help but I haven't tried it on the likes of M31, I've only use this method on nebula to date. You may have to do a careful stretch to try & control the core.  

[Budgie1]

Now I'm back in front of PI I wanted to clarify the wording for anyone reading this in the future and wondering what I'm going on about.

7 hours ago, Budgie1 said:

3. Restack all the subs using WBPP but use either a common filename (the proper name of this escapes me just now) or change the exposure limit setting to something like 300, so it stacks all of them into one master, instead of dividing them into individual masters based on the exposure length.

3. Restack all the subs using WBPP but use either "Grouping Keywords" or, on the Lights tab, change the "Calibration Exposure Tolerance"  to something like 300, so it stacks all of them into one master, instead of dividing them into individual masters based on the exposure length.

[Anthonyexmouth]

I couldn't get wbpp to stack my 4 stacks. Didn't like the low number. 

[Budgie1]

3 hours ago, Anthonyexmouth said:

I couldn't get wbpp to stack my 4 stacks. Didn't like the low number. 

No, I think you would have to run the whole stacking process again, using all the subs & calibration frames + changing the Calibration Exposure Tolerance.

If you want to use the four stacks you already have then try the Image Integration tool under Processes. 

[Anthonyexmouth]

24 minutes ago, Budgie1 said:

No, I think you would have to run the whole stacking process again, using all the subs & calibration frames + changing the Calibration Exposure Tolerance.

If you want to use the four stacks you already have then try the Image Integration tool under Processes. 

Thats what i ended up doing.

[old_eyes]

I may have misunderstood what you are trying to achieve, but why not use HDRComposition? That tool is designed for this job. It takes stacked images of different exposures and creates a high dynamic range version that allows you to see the detail from the long exposures whilst not having the bright core of objects burnt out. A standard approach for objects like M42 and M45. 

it is simple to use, and the tool works out which order to stack the images for the best result.

[Anthonyexmouth]

1 hour ago, old_eyes said:

I may have misunderstood what you are trying to achieve, but why not use HDRComposition? That tool is designed for this job. It takes stacked images of different exposures and creates a high dynamic range version that allows you to see the detail from the long exposures whilst not having the bright core of objects burnt out. A standard approach for objects like M42 and M45. 

it is simple to use, and the tool works out which order to stack the images for the best result.

I'll take a look at that. 

[Anthonyexmouth]

On 09/02/2023 at 10:48, Budgie1 said:

No, I think you would have to run the whole stacking process again, using all the subs & calibration frames + changing the Calibration Exposure Tolerance.

If you want to use the four stacks you already have then try the Image Integration tool under Processes. 

Update, when I tried to restack changing the tolerance to group them it seems to only be using one master dark, the longest exposure one, is this a problem or is it actually going to use all the right darks? 

[Budgie1]

13 hours ago, Anthonyexmouth said:

Update, when I tried to restack changing the tolerance to group them it seems to only be using one master dark, the longest exposure one, is this a problem or is it actually going to use all the right darks? 

So, in WBPP on the Calibration tab, does it list the different light frame groups separately? Does it do the same for the Darks/Master Darks?

If it does, what happens when to click on one of the light frame groups, what does it highlight the corresponding Master Dark, or just the longest exposure one for all of the Lights groups?

[ollypenrice]

Except on targets of truly extreme dynamic range (M42 ) I have always found it entirely pointless to shoot different sub lengths. Look at your linear data. If the core is not saturated at this stage, there is no need for it to be saturated at the end. That's down to careful stretching. Stretch it anyway, keeping the core down as best you can but accepting some saturation if you have to.

Next make a stack of as much of the shorter data as will give you an un-saturated core. Stretch that, concentrating on perfecting the parts which are saturated in the other.

Finally use an HDR tool or routine to blend them. Personally I use Layer Masking in Photoshop but there are lots of alternatives.

Olly