[Digikam-devel] raw problems

[Gilles Caulier]

2007/9/4, Arnd Baecker <arnd.baecker at web.de>:
>
> Hi,
>
> I was about to test the patch
> http://bugs.kde.org/show_bug.cgi?id=142055
> but before I wanted to look at that current status
> to see the difference.
>
> There are various problems in the following situation:
> Take the same image in the two versions RAW and JPG
> (as they come out of the camera, Canon EOS 350D for this example),
> with no color management enabled.
>
> Tests A:
> "RAW Files Decoding Settings"
> - 16 bits color depth
> - interpolate RGB as four colors
> + White balance: "Use camera white balance"
> + Automatic color balance
> + Highlights: Solid white
> + Brightness: 1.0
> + Interpolation: Bilinear
> - noise reduction
> - enable chromatic aberrations
>
>
> Tests A - results for the comparison of RAW vs. JPG
> ---------------------------------------------------
>
> - the thumbnails look very similar
>   (the histogram of a screenshot for each thumb
>    show only a small variation)
>
> - The histogramms for RAW and JPG differ considerably
>   (for the raw one all its weight is near small values).


Important point in general :

- RAW file are container :
=> RAW image data
=> metadata
=> JPEG preview image

This is want mean than RAW include a JPEG file ! This one is used to display
RAW picture very quickly on tv screen using camera device. This picture is
very similar than if you use your camera in RAW+JPEG mode, excepted than
JPEG image embedded in RAW is generaly smalless than a real JPEG picture
taken directly.

In digiKam we use this embeded JPEG image to render thumbnail and display
preview of RAW files if no whole image is used for that (check setup)

About histogram, RAW and JPEG histogram differt. It's normal : this is not
the same picture (in the same color space: JPEG = sRGB, RAW = linear).



> - BUG:
>   first going to the CR2 is fine, histogram is computed
>   (takes long!) and shown.
>   Then go to JPG - ok.
>   Then back to the CR2 - the "Histogram" TAB says
>   "Loading image" and this never finishes.
>   (will file a separate BKO for this)


yes, sometimes, i can reproduce it. This come from libkdcraw and
multithreading which use KProcess. Marcel, normally this bug must be fixed
in KDE3 branch or it's another probem with re-entrance of KProcess ?

Note : libkdcraw for KDE4 do not have this problem. It's a pure QT4
implementation which use QProcess & co...

Gilles
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