correcting weak histogram information?

Discussion in 'Digital Photography' started by neo, Jul 28, 2003.

  1. neo

    neo Guest

    hi all!

    is there a chance to correct weak histogram information? (lots of gaps
    in the curve!) - can this for example be done by superposing multiple
    copies of the same layer and combinging them ?

    thx markus
    neo, Jul 28, 2003
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  2. neo

    Mxsmanic Guest

    You can do it with curve adjustment.

    For example, if all the information in your photo is in dark and bright
    areas, with nothing in between (histogram with "humps" at either end,
    but a flat area in between), you can use Curves to fix this. In your
    Curves box, make the curve rise more sharply in the areas that have
    bumps in the histogram, and make it nearly flat in the areas that are
    flat in the histogram. The resulting image will have a more even
    histogram, and the interesting information in the image will be much
    more visible.

    This all depends on the image content, so the procedure varies for each
    photo, depending on what you have vs. what you want.
    Mxsmanic, Jul 28, 2003
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  3. If the gaps are from zero pixel count in smooth transitions, then you run a
    significant risk of posterization in the output. The most common cause is
    large tonal adjustments on an 8-bit (or high compresssion JPEG) image. Lost
    information cannot be retrieved.

    You can fill-in-the-gaps by either blurring, downsizing (or upsizing (+
    blurring) + downsizing + sharpening) or by adding noise. Adding noise may
    give the "best" image quality to avoid posterization, but you need a good
    photo editor to keep it almost invisible.

    Bart van der Wolf, Jul 28, 2003
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