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  1. #1
    Dublin sky watch's Avatar
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    Arrow How to remove Light Pollution from your image.



    It is difficult not to notice, how many of us budding astrophotographers get very depressed with the amount of LP in our local areas of observations. We can do only a few tricks to help our observing, but we can do a lot more when it comes to image processing.

    This is a quick guide on how to remove Light Pollution from your precious image.This can be done with either Photoshop or the free download software GIMP. They are both fairly similar to operate.

    1. After your image has been stacked open it up in your chosen software.

    2. If using PS, click..Layer..New Adjustments Layers..Levels and name it. The default histogram is RGB when it opens.
    With GIMP, click...Layer-Duplicate Layer..Colors-Level. The default histogram shown is VALUE when it opens.

    3. Use the drop down box and chose the red channel. The histogram display changes now to show this channel. Move the left hand slider over to the right until it is in line with the start of the steep rise of the histogram. Do not go beyond this steep point or you will clip the image and loose data.
    Notice That the image hue has also changed to a greenish tint.

    4. Repeat the process for the Green channel this time, again making sure not to clip your image. The image hue has now changed to a blueish tint.

    5. Repeat the process for the Blue channel finally again making sure not to clip your image. This time your image should have lost quite a bit of Light Pollution in the process.

    6. If I an satisfied with this outcome and you may need to play around to achieve the results you want for your particular image, I will stretch the image one last time by clicking Layer...New Adjustment Layer...Curves and name it. Depending on the type of effect your image needs, You can experiment with the curves tool, which is a really powerful tool.
    An S shape curve is a classic shape to use..but experiment

    Attached are two images I took from my backyard last December. The image is of The Plieades before and after using the above technique which is from a terrific little book called "Making Every Photon Count" by Steve Richards, which was recommended to me by Canon Pete some time back.

    I hope this will be of some help to some body in this community.
    Thanks.
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  2. The Following 11 Users Say Thank You to Dublin sky watch For This Useful Post:

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  3. #2
    Carolgentle's Avatar
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    Thanks Declan,

    I've got quite a few light polluted images, will give it a try.

    Carol

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  4. #3
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    Thanks Declan

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    Dublin sky watch's Avatar
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    It is basic, but it does work for an instant result...
    Declan.
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    Thanks Declan,
    Tried it on a few shots, very helpful!

    Clear skies

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    Dublin sky watch's Avatar
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    No problem adebaby...big game coming up soon...
    Declan.
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    Two men sat behind prison bars,One saw mud, the other saw stars. It's not where you are, it's what you see!!!

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    Quote Originally Posted by Dublin sky watch View Post
    ...big game coming up soon...
    Sorry to appear thick Declan, but i'm at a loss.......
    No doubt that i'll be kicking myself if you tell me!

  9. #8
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    [adeybaby
    Sorry to appear thick Declan, but i'm at a loss.......
    Sorry adebaby...my mistake. Its macman, he is a big Wolves supporter and I am a baggies supporter. Black country stuff...
    Sorry for the confusion..
    Declan.
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    Two men sat behind prison bars,One saw mud, the other saw stars. It's not where you are, it's what you see!!!

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    Thanks for this, still a noob and have a long way to go, but learning how to use Photoshop in ways I've never done before in the last 10+ years is really cool.
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    Dublin sky watch's Avatar
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    Its about experimenting Steve...lots of experimenting and what you find works for you.. and sharing it...
    Good job..
    Declan.
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    Explore Scientific - 127mm f/7.5 Air-Spaced Triplet ED.
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    orion star shoot solitaire autoguider.
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    Two men sat behind prison bars,One saw mud, the other saw stars. It's not where you are, it's what you see!!!

 

 
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