Question on masking...

[Aircrftr]

I have had several instances where it would be good if I could mask my DSO and then adjust the histogram of the background.  I've found that many times when I do the HDR Multiscale Transform, the area of my DSO have a background darker than the surrounding background in the rest of the pic.   Is there a way to mask my central object of interest while being able to adjust the background as needed (darken my background) ? Below is an example of what my situation is.  You'll notice what I mean in that the background is pretty bright while it seems my DSO has a background (in between the spiral arms and around the periphery of the galaxy) that is darker than the rest of the pic.

[georg.viehoever]

See  http://www.pixinsight.com.ar/en/docs/79/pixinsight-select-mask.html and the other videos on mask. There are also several examples on masking in http://www.pixinsight.com/resources/.
Georg

[Aircrftr]

I've read and looked at the videos and documentation in your links.  I'm sorry in that I haven't been too clear in what I wanted...
What I would like to be able to do is pull up a mask for my situation in particular for the image I posted, but more than that, in any case where I wanted to only modify a part of my image.  Ideally, what I would like to do would be to modify my mask like you are able to do in the ACDNR process.  That way I can adjust how much of the image I want to have masked.  Otherwise, I can only create a mask and invert it but I can't modify how restrictive the mask is.  Or is there a way to do that?

[NGC7789]

mask like you are able to do in the ACDNR process.

I believe if you apply the process while in preview mode you will get the mask.

-Josh

[Carlos Milovic]

Use Curves to adjust the intensity, and so, the masking effect.

[georg.viehoever]

The strength of the mask is determined by its value. So if a mask pixel has a value of 0.5, it keeps 50% of the effect of an operation away. It it has a value of 1.0, it protects a pixel entirely from any operation. If it has a value of 0.33, protection is only 33% etc. .  Is that what you need?
Georg

[Aircrftr]

Well, I know how masks work and I know that for my LRGB picture i'm wanting to modify, first I extract the luminance channel and put it on the bar of the RGB image, thus creating the mask.  NOW... I want to invert the mask which is easy enough, but how do I modify that masks pixel value before applying the histogram stretch to my RGB image?

[pfile]

just like any other image. you can smooth the mask with AtrousWavelets or gaussian blur, adjust the histogram of the mask itself with HT or Curves, etc.

there's really nothing special about a mask image… it just has to have the same pixel dimensions as the image it's being applied to. and you can manipulate it just like any other image, even while it's applied as a mask to another image.

rob

[Aircrftr]

Hmmm... OK. I'll play with it for a while and see what I come up with.
Thinking on this, after I extract the Luminance then put it on the bar of the RGB image, then the mask shows up as mostly in red, how do I modify that mask without modifying the image that the mask is on top of?

[Carlos Milovic]

The mask is not the red. It is the luminance image that you throwed to the color one. You have to modify the luminance image, and when a process is executed to the color one, it will call the external luminance. You don't have to update the mask status. It always looks for the external image, it does not use a internal copy.

[pfile]

oh, yeah i see the confusion. as carlos says the mask image is being continuously looked at by PI. if you change the mask image (the luminance image you dragged to the tab of the target) then the mask on the target image automatically changes. if for instance you take the mask image and make it incredibly bright (say, with HistogramTransformation, dragging the midtones slider all the way to the left), you'll notice that the red in the masked image completely obscures the image underneath. likewise if you make the mask image really dim, the red will hardly show up. the red thing over the masked image is simply there to give you some visual idea of how strong or weak the mask is.

rob

[Aircrftr]

   NOW I GET IT!   Thanks guys!  I extracted my luminance, then made my modifications to that luminance BEFORE I applied it as a mask.  Worked great.   Some times you just get tunnel vision on what you are trying to accomplish and completely miss the obvious.

Thanks guys!

Dan