[Digikam-devel] [Bug 170170] High quality 8 to 16-bit conversion (histogram repair)

[Dik Takken]

https://bugs.kde.org/show_bug.cgi?id=170170





--- Comment #4 from Dik Takken <d h j takken xs4all nl>  2010-01-26 12:11:35 ---
The noise is very subtle, just enough to fill the gaps in the histogram. On a
8-bit display, it is even impossible to see it. Only if you apply curves to the
image, the noise may become visible, provided that the image itself is clean.
You might try it on an 8-bit gradient. Create an 8-bit gradient, convert to
16-bit, repair the histogram and apply some extreme curve to it. If the
gradient repair plugin uses noise, you will see it now. Can anyone try this?

The algorithm for repairing the histogram after 8 -> 16 bit conversion looks
like this:

function RepairHistogram()
{
  for every pixel do
  {
    for every channel do
    {
      Pixel[channel].value += ( Random() % 256 )
    }
  }
}

Ideally, the histogram repair should be done automatically when converting from
8 to 16 bit. Image filtering plugins (like curves) should temporarily convert
the image to 16-bits and apply the noise to produce high quality 8-bit filtered
images.

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