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HDMRT and MLT

Roger Smith
in PixInsight
Hi Adam,
First, a little rambling...
I want to agree with you that your videos teach the meaning behind the processes. This is fundamentally important to doing processing with understanding vs just hoping for a result. A classical 'treasure hunt' comes to mind.
What I don't understand (amazing to me) is how Mr. Juan can be smart enough to create all the PI processes, having both the understanding what it is needed for an image, and how to do the math/scripting behind it. Yes, I understand he has others like you that do a huge amount of contribution behind the scenes, but he has to understand and agree and make them happen. As I said Amazing!

I do sometimes get confused or mixed up the order to apply different processes. Which is why an order of use outline from you would be great, focusing on post processing. Yeah, I know, Horizons shows the sequences!

Now to my question... For images, that from the beginning, we know will benefit from HDMRT, is MLT also needed? I mean why not just stretch the image to reveal the low brightness areas the first time we do a non-linear stretch?

Thanks,
   Roger

Comments

  • BlockHeadBlockHead
    Yes, I agree people like Juan (and other developers..in my earlier days it was Stan Moore) are amazing. They understand at a very deep level the math behind the algorithms. You might be surprised to learn however that they cannot foresee how the tools will be used- some of straight forward- but other tools develop a life of their own.

    With regards to the last question- the dynamic range of brightnesses of some object are so great that no simple/single  non-linear function does the job. HDRMT, MaskedStretch and other really do much more of this work- at least in a reproducible and easy way. 

    MLT isn't really involved in the compression of brightness levels- it is instead more of a noise/contrast tool at a given brightness you have settled on. 

    The example of NGC 5866 is a good one... virtually impossible to achieve what I think is a good result in any other way. Certainly repeated non-linear stretches (or maskedstretch) might approximate it..but I think it comes with a number of bad side-effects.

    -the Blockhead
  • Roger Smith
    Adam,
    Thanks for answering my questions. I was driven to ask about MLT vs HDMRT as I did not know if multiple usages increased noise in the image, which we want to avoid. So now I understand to do HDMRT in combination with other stretches. 
    Best regards,
       Roger
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