[Digikam-users] Questions on RAW conversion: Base curve

Elle Stone l.elle.stone at gmail.com
Wed Sep 11 12:22:49 BST 2013

In the digikam raw processing WB section there is "autobrightness"
which sets the white level (Gilles, yes?), which is not the same as
white balance. From the dcraw

By default, dcraw uses a fixed white balance based on a color chart
illuminated with a standard D65 lamp.

-w Use the white balance specified by the camera. If this is not
found, print a warning and use another method.
-a Calculate the white balance by averaging the entire image.
-A left top width height Calculate the white balance by averaging a
rectangular area. First do dcraw -j -t 0 and select an area of neutral
grey color.
-r mul0 mul1 mul2 mul3 Specify your own raw white balance. These
multipliers can be cut and pasted from the output of dcraw -v.

By default, dcraw writes PGM/PPM/PAM with 8-bit samples, a BT.709
gamma curve, a histogram-based white level, and no metadata.

-W Use a fixed white level, ignoring the image histogram. (Gilles,
this is autobrightness in the digikam raw processor, yes?)

This latter is the white level, not the white balance. The
corresponding line of dcraw code reads:

perc = width * height * 0.01;		/* 99th percentile white level */

By default (that is, unless you use "-W" at the command line) dcraw
will apply what amounts to a levels adjustment on your image, until 1%
of the pixels are solid white (clipped).  (I'm quoting an article I
wrote that annotates the dcraw c-code:
that article was the result of my quest to understand what raw
processing actually does).

Elle Stone

http://ninedegreesbelow.com - articles on color management & open
source photography

More information about the Digikam-users mailing list