Pixinsight Subraction

[spillage]

Hi All,

I have been following a tutorial on LVA regarding sharpening and am stuck on subtracting one mask from another.

"the star mask image was subtracted from the range mask image to produce a new mask image that has only got the bright nebulosity visible"

Is this done using pixelmath so starmask - rangemask with give you the result. I have tried to look everywhere but an struggling.

Cheers,

[geeklee]

6 minutes ago, spillage said:

Is this done using pixelmath so starmask - rangemask with give you the result. I have tried to look everywhere but an struggling.

Yep, you're right.  I've also worked through this one with a good result.  When you're subtracting, I believe you don't select "rescale result" (that's just for additive/multiplicative).  Just "Generate output" and Replace/New as required.

If you'd like some screenshots or further instructions, I can put those together this evening... or some experts will pipe up with more info shortly I'm sure!

[spillage]

Thanks for he advice Lee. I am still struggling a bit so screenshots would be great. I am slowly getting there but just need to remember what needs running first and what cannot be ran. I am used to using startools where you can do what you want when you want.

[geeklee]

Hi @spillage I've got some steps here that are from a quick galaxy mock up, but I think they're mainly repeating the stuff in the LV tutorial.

So you'll have a star mask (maybe called star_mask) and a range mask (maybe called range_mask).  These could have been tweaked in all sorts of ways.  I've done a bit of work on the range mask and star mask to match the type and softness a little.  You might have more binarized versions that are just black or white (no softness) - these work too and have their advantages.  

The LV tutorial is excellent at building up good masks initially before doing the subtraction.

I'll bring up PixelMath and fill in these fields:

Then click the blue square in the bottom left and you'll get output like the following:

If you selected "Rescale result" when you use a subtraction it will be obvious something has gone wrong:

For a galaxy I might get rid of all the stars around the target in a range mask then use the star removal part of this process to remove the stars that are tight around it and within. 

Remember, with PixInsight you've got a full History Explorer and can move back and forward through that as needed and quickly clone images.

Hope this helps and I've not way off in what you're looking for.

[spillage]

Thank you for that. I have now finally nail this bit. Time to conquer some more.