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Thread: Hot Pixels - night photography

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    Markvetnz's Avatar
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    Hot Pixels - night photography

    Here is a picture i took last week. There are a multitude of hot pixels all over the image. What is the best way to avoid these. This is a 20 min exposure. I turned the high iso noise reduction feature off in the camera. All help appreciated.

    Hot Pixels - night photography

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    Steaphany's Avatar
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    Re: Hot Pixels - night photography

    What you need to shoot with your image is a set of bias frames and a set of dark frames. Bias frames are created by keeping your lens cap on and shooting a succession of frames with a short exposure to get a baseline read out of the minimum pixel bias. Dark frames are also shot with the lens cap on, but now have the exposure identical to that used to capture your image. Unlike the bias, the darks will also contain the effect of the exposure integration time. Ideally, you should shoot a set of flat frames which capture a uniformly lit featureless surface.

    Your Bias, Darks, and Flats each need to be combined into single Master Bias, Master Dark, and Master Flat. These will be used with your light frames to process the image. The Bias will remove the effects of the base line imager noise and hot pixels. The Dark will compensate for the charge each pixel accumulates over the exposure integration time. The flats compensate for any optical variations that your lens imparts.

    For a complete and highly detailed explanation and software to fully characterize a camera or imager for astronomical photography, I recommend:

    Hot Pixels - night photography

    Alternatively, you can process your Bias, Darks, Flats, and image files with:

    DeepSkyStacker

    or

    RegiStax

    Both are free astronomical image processing packages, they'll be a bit tricky to get use to, but they, along with AIP4WIN, will make life easier and I've used these tools for astronomical and low light photography.

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    PhotomanJohn's Avatar
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    Re: Hot Pixels - night photography

    Awesome! I keep finding that I am never too old to learn something.

    Thanks,

    John

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    Markvetnz's Avatar
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    Re: Hot Pixels - night photography

    .... and I thought it would be a simple quick fix.

    Thanks for the links.

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    Re: Hot Pixels - night photography

    Quote Originally Posted by Markvetnz View Post
    ... There are a multitude of hot pixels all over the image. ...

    Hot Pixels - night photography
    Hi Mark,

    I've heard of hot pixels, but don't know what to look for in your image?
    Are they obvious or do you need to examine your photo at 100% or higher?

    Thanks,

    Erik

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    Markvetnz's Avatar
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    Re: Hot Pixels - night photography

    Quote Originally Posted by cichlid View Post
    Hi Mark,

    I've heard of hot pixels, but don't know what to look for in your image?
    Are they obvious or do you need to examine your photo at 100% or higher?

    Thanks,

    Erik
    Lots of little red and blue spots all over the image, especially in the dark areas.

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    Have a guess :)

    Re: Hot Pixels - night photography

    Hi Mark,

    ACR usually zaps the majority of them for exposures lasting a few minutes, but after that - personally - I just zap them manually. Using high ISO will make them much worse (you shouldn't need high ISO anyway).

    The other approach is to just just shorter multiple exposures, and stack them (TC-80N3 makes this dead easy - just set and forget whilst you keep warm with a sleeping bag and hot water bottle in the car; ahem, ... or so I've heard!)

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    Moderator Dave Humphries's Avatar
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    Re: Hot Pixels - night photography

    Quote Originally Posted by Colin Southern View Post
    ~ whilst you keep warm with a sleeping bag and hot water bottle in the car~
    Oh, the things you suffer for your hobby

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    Moderator Dave Humphries's Avatar
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    Re: Hot Pixels - night photography

    Quote Originally Posted by cichlid View Post
    I've heard of hot pixels, but don't know what to look for in your image?
    Are they obvious or do you need to examine your photo at 100% or higher?
    100% should do, more will help.
    Any downsizing, like this here, will probably render them invisible.

    I don't see why the can't be green too, but as each green image pixel is formed (in most sensors) by two green sensor pixels, they probably aren't as bright and will more easily merge into the image.

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    Re: Hot Pixels - night photography

    Quote Originally Posted by Dave Humphries View Post
    I don't see why the can't be green too, but as each green image pixel is formed (in most sensors) by two green sensor pixels, they probably aren't as bright and will more easily merge into the image.
    I don't know the exact reason as to why, but I haven't yet seen a hot pixel on my camera (or any other camera I have laid my paws on) that was a primary colour. Usually it is hot pink or bluegreen

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    victor's Avatar
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    Re: Hot Pixels - night photography

    Why use such a long exposure.

    Take 30 second exposures max and stack them with a programme such as Startrails.exe. Available from here http://www.startrails.de/. You can then reduce the ISO and avoid the build up of hot spots on your sensor.

    It works I have used it. See following:

    Hot Pixels - night photography

    Regards

    David

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    Re: Hot Pixels - night photography

    I have been wondering how to han dle these, thanks for the tip.

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