Correcting DSLR color channel clipping?

Discussion in 'Digital Photography' started by Antti Heiskanen, Sep 30, 2003.

  1. I have shot some photos with Canon 10D that have one color channel
    overexposed (the histogram was OK in the camera, but when I load the
    RAW-files in Capture One I see that e.g. red color channel is
    overexposed and as the result some areas in the photo are yellow). Is
    there any way I could try to adjust the photo to make it usable? I
    understand that if any channel is clipped then the image is spoiled
    (overexposed image information is lost), but I suppose there should be
    something I could try to do to reconstruct a reasonable unclipped
    image.

    Some ideas that come to mind are:

    - using linear RAW-conversion (or combined linear + normal
    conversion) to get more dynamic range (I have a vague idea that
    someone somewhere has mentioned this, but more information and tips
    how to do it are needed).

    - I could try to copy data from blue or green channel to overexposed
    red channel and then do color correcting if needed (would this help?)

    - I could measure white balance in difficult shooting conditions and
    use the corrected white balance for shooting (e.g. very dimly lit
    interior where main light source is the fireplace is a shot that is
    bound to have red channel clipped as most of the tones in blue and
    green channel histograms are on the left end, but tones on the red
    channel are on the right). Corrected WB might result in losing some of
    the mood, but that could be corrected later in RAW-conversion. --> I
    doubt this would work, as WB can be adjusted in RAW-conversion phase
    and therefore shooting-WB does not actually play a very large role.

    - In difficult shooting conditions I could always take two exposures
    from tripod (one underexposed to record detail on the channel that
    would probably otherwise be clipped, and one normal or overexposed
    picture to record detail from the other channels) and then combine the
    images in Photoshop. This requires quessing, more work and taking
    multiple images, but is probably the most likely way to get good
    results?

    Would these work or are there any other possible solutions?

    -Antti
     
    Antti Heiskanen, Sep 30, 2003
    #1
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  2. Antti Heiskanen

    Lionel Guest

    Word has it that on 30 Sep 2003 02:18:21 -0700, in this august forum,
    (Antti Heiskanen) said:
    If you shot in RAW mode, try dropping the exposure compensation a stop
    or two in your favourite RAW-manipulation program. Unless your image is
    really horribly overexposed in the red channel, that should bring it
    under clipping level.
    Also, before converting & tweaking the image itself, do check to make
    sure that your WB is set for something approximating the actual lighting
    in the original scene, as I've noticed that all the usual programs will
    cheerfully blow out the red channel if the WB is a long way from
    reality.
     
    Lionel, Sep 30, 2003
    #2
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