on Tuesday 11 May 2010, Rei Shinozuka wrote:
>
> In DNG images with large areas of overexposure, entering the Image
> Editor renders a color cast, often magenta or yellow. It almost
> resembles a stain on the image. Color casts do not appear when looking
> at the DNG in album mode, nor in the simultaneously-created in-camera
> JPGs, but only in the digikam Image Editor.
This can happen depending on how dcraw treats overexposed areas:
apparently one channel saturates faster/earlier than the others, so in
unclipped mode there is a cast of the colour of the remaining channels.
album mode uses a camera-generated preview jpeg, where the in-camera software
prevents this (by clipping the other channels as well? no idea)
> If the image is saved from
> Image Editor as a jpg, the color cast is present in the output file.
Of course, if in the image editor you see a color cast, that SHOULD be
preserved in the output...
> The color cast only seems to happen in areas which appear to be 100%
> white, absolutely burnt out highlights, though it does not precisely
> coincide by areas marked by the overexposure indicator.
It is an over-exposure phenomenon.
>
> I can provide sample images demonstrating this phenomenon.
>
> digiKam Version 1.2.0 Using KDE Development Platform 4.4.2 (KDE 4.4.2)
> 2.6.32-22-generic #33-Ubuntu SMP
I suppose image editor opens in the 'Raw Import' mode. In that case, check
under 'White Balance - Highlights:' if it shows 'unclipped' then there's the
cause, try changing to one of the others (Solid White is a good start to
check, see manuals for other options)
Remco
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