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Thread: 'Hot pixels!'

  1. #1
    drmytan
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    'Hot pixels!'

    Recently l tried long exposure shots with my H4D31 and just realised this camera only gave the bulb maximum time of 64sec ... how to use my newly purchased Lee's big stopper 10x filter?
    Now my real question is l noticed especially when using the wide-angle lens of 28mm together with filter (CPL or ND) and with longer exposure l noticed red and blue pixel type patches/spots on the shadow areas. Are they called 'hot pixels' due to the long exposure generating the heat on or from the sensor as explained by my dealer here? Sorry l am not the technical genius but love to shoot photos only.
    How on earth can l reduce this? By not doing the long exposure shot, so what is the ideal exposure time to avoid this sort of artifacts? Any software to overcome it? Anything in the camera setting to use to stop it? Editing by photoshop doesn't help much.
    Is it possible to increase Bulb time beyond 64sec (after l have solved my problem of 'hot pixels')? Otherwise no point of doing more than 64sec if one still gets the hot pixels.
    Thanks for any comment and suggestions

  2. #2
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    Re: 'Hot pixels!'

    Did you process the image with Phocus? I have never seen a hot pixel shooting up to 4 minutes on my 40, and 64 seconds on the H3D 39.
    Cheers,
    Jeff
    www.jeff-grant.com

  3. #3
    drmytan
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    Thumbs up Re: 'Hot pixels!'

    Quote Originally Posted by Jeffg53 View Post
    Did you process the image with Phocus? I have never seen a hot pixel shooting up to 4 minutes on my 40, and 64 seconds on the H3D 39.
    Thanks
    Yes all the images are open and processed with Phocus then edited in Photoshop CS5. Which function in Phocus can l use to reduce these artifacts?

    Regards

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    Re: 'Hot pixels!'

    There is no function that I know of. I have seen hot pixels appear while Phocus is processing a file but they disappear as soon as it is processed. Can you post an example? Also are you using the standard settings when importing?
    Cheers,
    Jeff
    www.jeff-grant.com

  5. #5
    drmytan
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    Re: 'Hot pixels!'

    Quote Originally Posted by Jeffg53 View Post
    There is no function that I know of. I have seen hot pixels appear while Phocus is processing a file but they disappear as soon as it is processed. Can you post an example? Also are you using the standard settings when importing?
    After the minimal process done in Phocus, l export it out as Tiff 16 (chose 16bit) with resolution 360 ppi file. Then open it in PS to continue more pp work.

    Thanks

    Cheersv

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    Re: 'Hot pixels!'

    Sounds like it's time to call your friendly Hasselblad man.
    Cheers,
    Jeff
    www.jeff-grant.com

  7. #7
    Workshop Member Wayne Fox's Avatar
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    Re: 'Hot pixels!'

    Did you have the dark frame subtraction option enabled on the camera when you took the picture? Normally the camera masks out these pixels with this process.
    wayne
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    Re: 'Hot pixels!'

    It's not a choice on a Hasselblad. They don't do dark frame.
    Cheers,
    Jeff
    www.jeff-grant.com

  9. #9
    Member carl-b's Avatar
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    Re: 'Hot pixels!'

    Try opening a file directly in ACR, that has known effect with hot pixels with some camera's. I will see if i can find the link for the information on it.

    http://forums.dpreview.com/forums/re...ssage=30696618

    http://www.openphotographyforums.com...php/t-181.html

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    Re: 'Hot pixels!'

    I notice you are in Malaysia. Do you shoot in warm temperatures and high humidity? As you know, integration noise (thermal or dark current noise) is temperature dependent (doubles with about a 6'C increase) and the CCD can really heat up if ambient cooling is not working well. Long exposures work better in the winter - where there is a winter. Stick the camera in a fridge and then qiuckly take the same image. That will tell you if you are seeing an integration noise issue.

  11. #11
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    Re: 'Hot pixels!'

    For my P65+ I just apply a 1 pixel dust and scratch filter in Photoshop. That clears up nearly all of the hot pixels,

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    Workshop Member Wayne Fox's Avatar
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    Re: 'Hot pixels!'

    I didn't know hasselblads didn't do that, since it's pretty standard for digital cameras. Seems to be a curious omission. Sounds like it might be worth trying to do this manually, such as this person suggests for star photography.
    wayne
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    Re: 'Hot pixels!'

    Wayne, the Hasselblad backs have the dark frame info built in. It's not an omission, it's a benefit.
    Cheers,
    Jeff
    www.jeff-grant.com

  14. #14
    drmytan
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    Re: 'Hot pixels!'


  15. #15
    drmytan
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    Re: 'Hot pixels!'

    Quote Originally Posted by cunim View Post
    I notice you are in Malaysia. Do you shoot in warm temperatures and high humidity? As you know, integration noise (thermal or dark current noise) is temperature dependent (doubles with about a 6'C increase) and the CCD can really heat up if ambient cooling is not working well. Long exposures work better in the winter - where there is a winter. Stick the camera in a fridge and then qiuckly take the same image. That will tell you if you are seeing an integration noise issue.
    Well! l live in Malaysia but l travel often and only use it when l go oversea. I usually travel to the temperate countries. Thanks

  16. #16
    drmytan
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    Re: 'Hot pixels!'

    Quote Originally Posted by carl-b View Post
    Try opening a file directly in ACR, that has known effect with hot pixels with some camera's. I will see if i can find the link for the information on it.

    Help: Adobe Camera RAW 5.2 NOT Mapping out Hot Pixs on 5D2: Canon EOS-1D / 1Ds / 5D Forum: Digital Photography Review

    The hot pixel issue [Archive] - Open Photography Forums
    Thanks. Will have a look at it.

  17. #17
    drmytan
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    Re: 'Hot pixels!'

    Hi guys .. first of all as referred to my questions, l am still not clear how the hot pixels look like. What l mentioned at the top is the information l had from the retailer. Looking at the picture taken in Prague recently, l noticed some pixel artifacts on the shadow areas around the dark water when zoomed in. Are they the hot pixels?
    Maybe can someone show me how the hot pixels look like.
    THANKS

  18. #18
    drmytan
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    Re: 'Hot pixels!'

    Quote Originally Posted by Craig Stocks View Post
    For my P65+ I just apply a 1 pixel dust and scratch filter in Photoshop. That clears up nearly all of the hot pixels,
    Hi! Thanks for the info on this. Sorry whereabout exactly these functions can be found in CS5?
    Cheers

  19. #19
    drmytan
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    Re: 'Hot pixels!'


  20. #20
    drmytan
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    Re: 'Hot pixels!'


  21. #21
    drmytan
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    Re: 'Hot pixels!'


  22. #22
    Workshop Member Wayne Fox's Avatar
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    Re: 'Hot pixels!'

    Quote Originally Posted by Jeffg53 View Post
    Wayne, the Hasselblad backs have the dark frame info built in. It's not an omission, it's a benefit.
    How can you build it in? it varies based on exposure time and temperature. You can calibrate out some of it, but then pretty much every camera maker does that as well.

    Didn't seem to work for the OP.
    wayne
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  23. #23
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    Re: 'Hot pixels!'

    Quote Originally Posted by Wayne Fox View Post
    How can you build it in? it varies based on exposure time and temperature. You can calibrate out some of it, but then pretty much every camera maker does that as well.

    Didn't seem to work for the OP.
    I think that is up for debate at the moment. He does say that he doesn't actually know what a hot pixel looks like. I don't see any. Maybe David Grover can step in. All I know is that it works for me, and has done so since the H3D.

    Here's a link to 'no dark frame' in action: http://forum.getdpi.com/forum/medium...utes-plus.html
    Last edited by Jeffg53; 30th March 2012 at 22:56.
    Cheers,
    Jeff
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  24. #24
    Workshop Member Wayne Fox's Avatar
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    Re: 'Hot pixels!'

    Quote Originally Posted by carl-b View Post
    Try opening a file directly in ACR, that has known effect with hot pixels with some camera's. I will see if i can find the link for the information on it.

    Help: Adobe Camera RAW 5.2 NOT Mapping out Hot Pixs on 5D2: Canon EOS-1D / 1Ds / 5D Forum: Digital Photography Review

    The hot pixel issue [Archive] - Open Photography Forums
    wow, those links are old ... any evidence the issue still exists? They're talking about ACR 5 (7 is due any time now) and the other thread is older than that.
    wayne
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  25. #25
    Member carl-b's Avatar
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    Re: 'Hot pixels!'

    Quote Originally Posted by drmytan View Post
    Hi! Thanks for the info on this. Sorry whereabout exactly these functions can be found in CS5?
    Cheers
    When the image is open in CS5 go to - filter - noise - dust and scratches

  26. #26
    Member carl-b's Avatar
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    Re: 'Hot pixels!'

    Quote Originally Posted by Wayne Fox View Post
    wow, those links are old ... any evidence the issue still exists? They're talking about ACR 5 (7 is due any time now) and the other thread is older than that.
    Yes Wayne, people are still saying ACR removes the hot pixels. Apparently it was Thomas knoll who wrote that bit into ACR

  27. #27
    drmytan
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    Re: 'Hot pixels!'

    Quote Originally Posted by carl-b View Post
    When the image is open in CS5 go to - filter - noise - dust and scratches
    Thanks

    Cheers

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