Dynamic range tutorial

[andrewluck]

I'm having some trouble working through Vicent's dynamic range and local contrast tutorial. When I get to the stage around figures 14 & 15 I can't work out how to iteratively apply the pixelmath process. As MS - MS_LS + HDRWT_LS  isn't changing after an application of the process how do I apply this in multiple stages?

Andrew

[oldwexi]

Hi Andrew!
If you drag and drop the PixelMath triangle over the image  "MS"
the image "MS" will always change after each drag and drop -  if
MS_LS and HDRWT do have different values.

Gerald

[andrewluck]

Thanks Gerald

Trouble is, I can't see that works either. I'm having difficulty getting my head around what's happening here.

I can see that the pixelmath transform will replace the large scale structures in the MS image with HDRWT_LS. But this process is being masked and the mask is red over the areas in the MS image that contain the large scale structures that I'm trying to replace. It seems to me that the transform should be applied to the HDRWT image but then I get the problem that subsequent iterations don't do anything.

Cheers
Andrew

[oldwexi]

OK.!
If a mask is in the game than "it depends".

For a test of the "no Change" in iterations
we need the 3 mages and the mask.

Gerald

[andrewluck]

Files are uploaded:

https://www.dropbox.com/s/stxrmh2k080ntch/HDRWT_LS.xisf?dl=0
https://www.dropbox.com/s/67fz5a5y2e0mll8/HDRWT.xisf?dl=0
https://www.dropbox.com/s/8kg35bzm4yelpo9/mask.xisf?dl=0
https://www.dropbox.com/s/fegfk2rwdhf77hc/MS_LS.xisf?dl=0
https://www.dropbox.com/s/3nfijspmhd3azo5/MS.xisf?dl=0

Thanks for any help
Andrew

[oldwexi]

Hi Andrew!
The expression   MS - MS_LS + HDRWT_LS  is working.

Your mask is very dark. Therefore only a very small change, nearly(!) unvisible happens.
But,
if you open the Statistics Process from the beginning, you can see the small change in numbers
each time you drag and drop the triangle. (Dont forget to enable the Statistic process to the active
image.(lower right corner).)

If you run the PixelMath 6 times than you can also see it.
Switch in the HistoryExplorer between 1st Layer and 6th Layer this shows clearly the increase of the star size.
according to the starmask you are using.


I dont know what you really wanted to achieve, but tiny changes are done.

Gerald

[andrewluck]

Thanks for looking at the images Gerald.

As it's written, the tutorial doesn't appear to do what it's supposed to. It should use the stars from the masked stretch with the large scale structures from the HDRWT image. You've confirmed what I see; i.e. this doesn't happen, even over several iterations. I think I'm missing something.

Hopefully Vicent will be able to clarify this.

Cheers
Andrew

[oldwexi]

Hi Andrew1
The star mask is not stretched, it is much to dark, therefore suppresses all PixelMath Actions.
Gerald

[andrewluck]

Hi Gerald

The tutorial refers to the mask only having an intensity of 0.1-0.2 which matches mine.

As I see it, the problem is that this operation is supposed to transfer the small scale detail from the MS image to the HDRWT image. I think that can only be done by applying the mask to the HDRWT image and then applying the pixel math operation to it. But, if I do that, subsequent iterations which the tutorial mentions don't do anything because the MS image hasn't changed.

Here's the link to the tutorial: http://pixinsight.com/tutorials/NGC7023-HDR/index.html

Puzzled

Andrew

[andrewluck]

I eventually solved this from another direction. As the objective was to replace the small scale structures in the HDRWT image with those from Masked Stretch I simply used the mask created by subtracting one image from the other created earlier in the tutorial and applied it to the HDRWT image. I then used PixelMath to superimpose the MS data.

Not sure if this was the effect as originally intended by Vicent but it'll do for now.

Andrew