W
hile there are several solid open source
RAW processing applications available
(such as Photivoand RawTherapee), enabling
RAW support in GIMPsignificantly simplifies
the digital photographic workflow. Which
plug-ins and scripts you choose will depend
on your specific needs, but there are several
modules that are essential for any user
who wants to use GIMPas an all-round
photographic tool. These include UFRaw
plug-in (http://ufraw.sourceforge.net/), which
is included on this issue’s free DVD.
Although UFRawacts as a helper module
in GIMP, it is also a powerful RAW processing
tool. UFRaw relies on the excellent dcraw
RAW decoding library (http://www.cybercom.
net/~dcoffin/dcraw/) and can handle a
wide range of RAW formats (see the list
of supported cameras at http://ufraw.
sourceforge.net/Cameras.html). Thanks to the
LittleCMS software (http://www.littlecms.
com/), UFRawsupports ICC color profiles,
providing you with full color management
support. Nikon users will also appreciate
the fact that UFRaw can read Nikon
camera tone curves. In short, if you shoot
in RAW, installing the plug-in should be
high on your list of priorities. During the
installation process, you will be prompted
to associate RAW files withUFRaw, and
you should do this if you want to use
the UFRaw/GIMPcombo as your primary
RAW processing tool.
If you are a GIMPbeginner, we recommend
that you read our GIMPMaster Class in Issue 2
of c’t Digital Photography(page 56ff). This
issue is unfortunately out of print but is
available digitally at http://www.ct-digiphoto.com.
GIMP’s main image processing tools are easy
to find, but work in a way that might not be
intuitive to users of other imaging software,
so this introduction will help to get you
started.Working with UFRaw
The UFRawinterface is split into two panes.
The preview pane to the right displays a
preview of the currently open RAW file, and all
adjustments you make to the file appear here
in real time. The left pane contains the RAW
histogram with conversion curves and the live
histogram, as well as a tool palette that
contains several tabs of its own. The exposure
compensation slider below the RAW
histogram allows you to manually adjust
exposure settings. Alternatively, you can use
the ‘Auto adjust exposure’ button to let
UFRawmake its own settings. The White
Balancetab contains all essential tools for
tweaking white balance settings. Like other
RAW processing tools, UFRaw offers severalways to adjust white balance – you can
choose one of the many presets from the
White Balancedrop-down list, or use the
Temperatureand Greensliders and the color
picker tool to tweak white balance manually.
The Bayer pattern interpolationdrop-down list
gives you a choice of demosaicing algorithms.
By default,UFRawuses the AHD interpolation
algorithm, but you can experiment with the
other included options to see if you prefer the
results. Once the interpolation algorithm
has been applied, you can use the ’Color
smoothing’ button to reduce color artifacts
such as pixel noise and other blemishes. The
Denoiseslider offers a quick and simple way to
reduce digital noise in RAW files, while the ’Hot
pixels’ feature can help you to counteract the
effects of hot pixels in your image.
In the Base Curvetab, you can tweak
brightness and contrast settings by adjusting
the base curve, which imitates Nikon’s native
tone curve. You can adjust the settings
manually or import an existing .ntc-format base
curve. If you don’t have any curves of your own,
you can download and try out curves from
the Fotogenetic website at http://fotogenetic.
dearingfilm.com/downloads.html, and you can
save manually adjusted curves in the plug-in’s
own .curve format for use with other RAW files.
UFRawsupports color management, and
the Colors page on the project’s websiteGIMP Add-ons | RAW Development- UFRaw enables you to
process virtually all known
RAW formats and includes all
the basic tools you need for
developing digital negatives
2. UFRaw’s base curve
functionality emulates the
Nikon tone curve feature.
It directly supports .ntc
tone curves and enables
you to import existing
curves and apply them to
RAW files.