Mask, problem to seperate M51 and big stars

[Dominik]

Hello !

Well, i'm trying to solve a problem wich is certainly a classic one, but i don't know how to do ...

So i have an image of M51 taken with my Canon 350D. The image contains of course M51, little stars and some "biggers" stars.

I want to create a mask to be applied only on M51, to be inverted and permit me to apply processes only on the galaxy.

So I thought i could do this :
- create a star mask with Star Mask process
- duplicate my image to create my final mask
- apply the star mask on the duplicated image
- use the histogram to remove stars
- then I have my mask with no stars, so I have a mask only for my M51.

But I can't achieve that because I don't succeed in building a star mask with all the stars and without parts of M51 :
- if I create a star mask without any part of M51, the bigger star are not in the star mask
- and If I create a star mask with the bigger stars (i try to increase the scale parameter), some parts of M51 always appear in the mask.

So I can't "separate" the structure of M51 and my big stars.

I don't know if it's clear  ---

Perhaps a solution in Star Mask parameters or in preparing my clone in certain way before using star mask ?

[Zocky]

Maybe you could try with RangeSelection. It has a preview and all you have to do, is to play around with sliders until you get the result you want.

[Dominik]

Well I try this but same problem ...

[Phil Leigh]

Create a range mask covering stars+galaxy... create a star mask and then subtract the star mask from the range mask using PixelMath ?