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Thread: Exposure and de-mosaicing?

  1. #1

    Join Date
    Dec 2010
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    Exposure and de-mosaicing?

    Can anybody tell me if when a pixel gets overblown in raw mode, does it bleed over into surrounding pixels, or is that an artifact of whatever display mode/de-mozaicing you are using to view it?

    Does ACR/Lightroom Recover work on single pixels, or does it it also operate to try to recover bleed over?

  2. #2

    Join Date
    Dec 2008
    New Zealand
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    Have a guess :)

    Re: Exposure and de-mosaicing?

    Good question Tim,

    My understanding is that it can/does affect surrounding pixels, although I'm not sure to what degree.

    In terms of ACR / LR recovery, I'm really not sure to be honest -- in most cases the issue is probably going to be affecting a group of pixels in an area.

  3. #3

    Join Date
    Nov 2009
    Provence, France
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    Re: Exposure and de-mosaicing?

    One important thing to keep in mind here is that pixels in the RAW data have only information for one colour (cf. Bayer matrix). In order to get to 3-colour pixels, you need interpolation from the neighbouring pixels. How many pixels are used for that interpolation depends on the algorithm used.

    Interpolation implies that information from those neighbouring pixels is used, so blown pixels in the RAW will bleed (I can see that nicely from some hot pixels in longer exposures, which give a cross in the final image).

    If a pixel gets overblown due to an error in the sensor (stuck or hot pixels), you could use black frame subtraction to remove them prior to interpolation/dematricising(?):
    take an picture with the same iso/f-stop/time settings as the image you want, and with the lens cap in place to get a black frame, which the software you use can subtract from the 'real' image.

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