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HDRMT working in opposite direction for preview and full image???

Frédéric Ruciak
in PixInsight
Hi Adam, 
I am now processing my first image of M13. WBPP, DBE, SPCC, BXT, NXT in linear stage went well. Now I am facing the traditional issue of the very bright core. I tried HDRMT with a mask for the globular (to lightness, lightness mask) . First I switched to non linear with permanent streching, the core getting close to 1 but not yet. On the preview of the globular it works perfectly well, I can see the effect of varying the number of layers. But I don't understand why it works the opposite way on the whole image, ie the core becomes brighter when I apply the same HDMRT to the whole image.
I really do not understand where it comes from knowing that I have a mask isolating the globular itself (red everywhere else).
first attached is the preview and second attached is the zoom on the globular from the full image after the same process HDMRT.
Thank you for your advice to solve what looks as an enigma for me.
Frédéric

Comments

  • BlockHeadBlockHead
    Hi Frederic,

    I explain this in detail in a number of sections on HDRMT. 
    HDRMT uses wavelets- a spatio-frequency function. This function is correlated with the number of pixels that are being operated on. So the size of the frame will give you a unique answer. The more things that are bright in the frame- the greater the flattening/compression effect. This is why I teach that you should make a preview that gives you a good HRDMT result and *substitute* this preview into your image to get that same exact result. You will not have the same result if you use HDRMT on a preview and then apply to the entire image. 

    This is one of the reasons that a kind fellow created the Substitute script. (See this video). It will do this trick for you in a single step.

    -the Blockhead
  • Frédéric Ruciak
    Hi,
    Sorry, I was so impatient to use it that I did HDMRT on M13 before the last video on HDMRT where you explain this. I discovered my mistake in the last video with the substitute script this morning.
    Thanks again, Frederic
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