Combining NB with RGB in a galaxy

[k8jb]

Been using the NBRGB tool and it works great for nebula imagery so I thought I'd try it combining NB in a galaxy image.  The galaxy NB shows the core and HII regions so when I do the combine, the galaxy comes out green...I tried masking just the HII regions but the mask doesn't seem to work.  Also tried the old extract-channels/pixel math/combine channels, etc, method and again the mask doesn't affect anything.

So two questions: how do you apply a mask to an image and save just the masked results? I can't seem to find a method to do that.

Second, I would appreciate someone pointing me to a technique to combine galactic HI regions to an RGB image.

Tnx


John

[drmikevt]

John

It is quite a bite to chew on, but here is Vincent's approach (one of the authors of many of PI's tools) to combining Ha and LRGB data.  Take some time with it - it is advanced, but should give superior results to other methods.  Good luck!

http://pixinsight.com/tutorials/narrowband/

In reference to your mask question - I'm not sure what you are asking.  What are you talking about when you say, 'the masked result'?  You can not permanently save an image with a mask applied, if that is what you are asking, but I'm not sure why'd want to do that anyway.  Depending on what you are trying to do, there is almost certainly a work around, however.

Mike

[RickS]

Here's an example of adding Ha regions to a galaxy image: https://pixinsight.com/forum/index.php?topic=11526.msg71402#msg71402

I don't quite understand your question about masks.  Is it possible that you accidentally disabled the mask?  In the example above I apply a mask that protects everything in the image except the areas of strong Ha, then use CurvesTransformation to bump up the red and to a lesser extent, the blue.  After applying CurvesTransformation the working image has been modified.  There's no need to "save just the masked results."

Cheers,
Rick.

[k8jb]

Thanks for the help, guys, I'll checkout the links you provided.

Regarding my mask question:  I had attempted to apply a mask to my H alpha image and use it in the NBRGB tool thinking I should mask out the core of the galaxy (big, bright M31 was my first galactic target with a new OTA and camera).  I can see the HII regions but the core is overwhelming.  When the mask did nothing (I checked to make sure it was enabled), I thought perhaps there might be a way save a masked image to just save the parts passing through the mask (ala Photoshop).

Thanks, again, now I have some work to do...


John

[RickS]

Regarding my mask question:  I had attempted to apply a mask to my H alpha image and use it in the NBRGB tool thinking I should mask out the core of the galaxy (big, bright M31 was my first galactic target with a new OTA and camera).  I can see the HII regions but the core is overwhelming.  When the mask did nothing (I checked to make sure it was enabled), I thought perhaps there might be a way save a masked image to just save the parts passing through the mask (ala Photoshop).

Ah, that makes sense now.  A script can perform a lot of operations including copying the source image, applying new masks, etc. so it's generally risky to assume that a script will behave in the way you were hoping.  What you can do is take a copy of the original image, apply the mask and then copy the image processed with the script over it using PixelMath.  This will overwrite only areas left unprotected by the mask.

Cheers,
Rick.