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Elephant Trunk Nebula in SO/HaL, 



    
        

            David McClain

Elephant Trunk Nebula in SO/HaL

Getting plate-solving status, please wait...
Elephant Trunk Nebula in SO/HaL, 



    
        

            David McClain

Elephant Trunk Nebula in SO/HaL

Acquisition details

Basic astrometry details

Astrometry.net job: 1060201

Resolution: 3306x2484

Description

Raw frames courtesy of Deep Sky West Remote Observatory in New Mexico, USA. (deepskywest.com) Data obtained with FSQ 106EDXiii / QSI683wsg / Lodestar / Paramount MyT.

Approx 25 hrs total integration (16x1800s O-III, 18x1800s S-II, and 16x1800s H-alpha). The palette is SOO with R = S=II, G = O-III, and B = O-III, and with H-alpha serving as Luminance.

This is really a bi-color image with H-alpha Luminance. The central region appears relatively starved of S-II and dominated by O-III. The choice here is what color to make O-III. By all rights it should be a greenish color at 501 nm. But we can stretch the color-space contrast, making it more blue.

At any rate, red areas are dominated by S-II, and blue/green areas by O-III. In truth, the whole nebula is hugely dominated by H-alpha and dust. S-II and O-III make up a much weaker component of the nebula. Everything out there is dominated by H-alpha. So for a change, let's not look directly at that.

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Sitting here pondering the color mapping situation. NASA likes to use SHO (R=S, G=H, B=O) and we have seen some mighty pretty pics done in this mapping. I think they look so good because with a proper choice of H-alpha weighting (10-20%) the central regions of many nebula take on a pleasing blue-green backdrop, much like a daylight sky. And that helps the dark cloud features really stand out.

But truth is, both NASA SHO and CFH HOS color palettes try to stuff a redundant color somewhere in the RGB palette, and you get those nice pics. But both H-alpha and S-II are really red and nearly on top of each other. And so there are really two unnatural color assignments in NASA SHO, and one unnatural color assignment in CFH HOS.

So, from a science perspective, I think I'm beginning to prefer this SOO palette and using the much stronger H-alpha signal to develop a really deep detail Luminance channel. That mixes 3 important components into the image without any redundancy.

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Revision gets rid of the red halos around the stars.

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Revision (artificially) remaps magenta to a white'ish color. Magenta regions are where both S-II and O-III are present. But magenta is difficult to discern visually when right next to red. By remapping, we highlight those mixed regions, and also increase the contrast of the streamer wafting to the left off the column, against the blue background.

In a tri-color image, when all three colors are present in roughly equal amounts, you get a shade of white. So by analogy, in a two color image, when both components are present, we make the RGB system show us a white shade.

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Revisioin adds slight enhancement of wavelet layers with scale-lengths between 8-32 pixels, with declining weights toward longer scale lengths. Brings out many details in the dark clouds.

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Revision backs up, uses cleaner processing to remove chrominance noise, stretch brighness in Ha to mid-range in core of nebula, less harsh detailing, fewer strong black-worms.

Comments

Revisions

  • Elephant Trunk Nebula in SO/HaL, 



    
        

            David McClain
    Original
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            David McClain
    B
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            David McClain
    C
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            David McClain
    D
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            David McClain
    E
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            David McClain
    F
  • Elephant Trunk Nebula in SO/HaL, 



    
        

            David McClain
    G
  • Final
    Elephant Trunk Nebula in SO/HaL, 



    
        

            David McClain
    H

Histogram

Elephant Trunk Nebula in SO/HaL, 



    
        

            David McClain