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LRGB combination

Grigory Vidishev
in PixInsight
Hi Adam,
Thank you for the excellent videos you are producing.
I follow your practice examples in Horizons and all is good until I combine luminance image with RGB. My result is actually comes out worse and it is not what you get in the lesson. I cannot do exactly the same way of stretching and probably this is where we differ and it is carried through to that important stage of the processing. I do realize that luminance image should not have values not more than 0.8, but still even when I try to make it lower I am not always successful.
Question: what is the requirement for the luminance image to make it a successful blend with RGB? Sometimes, I can fiddle with Saturation and Lightness in LRGB Combination Tool and it helps, but I would like to know the logic and theory behind that. I also tried Blend script and it is normally not helpful if I cannot do it in LRGB Combination tool.
Attached is just an example of my fiasco on NGC6888 processing.

Thank you,
Grigory

Comments

  • BlockHeadBlockHead
    Its complicated. The method I teach is the most flexible- there isn't a set recipe because it depends on the data. The logic is that brighter values lose color. The theory deals with color spaces and the math for how they are rendered on devices like monitors. This is something I am not an expert in and it goes way beyond what is appropriate for Fundamentals. It is beyond me.

    One way to get close is to find a luminance stretch that is "gray" without many too high values. Then you can do a Linear Fit on the RGB image to make it "match" the Luminance. This can get you closer to a good result when you subsequently use LRGB. 

    There is another technique that I intend to highlight that will also be helpful. I need to make this video as well. There is a way to combine the luminance and color in the Hue/Intensity space that can make it easier for some data.

    -the Blockhead 
  • Grigory Vidishev
    Thank you Adam. I did not think about Linear Fit in this context and I will try that. To me understanding of Luminance and how it impacts the final image in combination is an important factor to a successful image. 
    Thank you again,
    Grigory
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