The Showfoto Handbook
Third, in case anyone isunsure onthis point, note that an interpolated raw ﬁle isno longer a raw
ﬁle - it has beeninterpolated andthenoutput asatiff whose RGB valuesneed to be translated to a
working space, using the camera proﬁle, the PCS, and lcms. Fourth(strictly for future reference),
to introduce a bit of commonly heard color-management terminology here - the camera proﬁle
and your printer’s color proﬁle are both device dependent, whereas the working space will be
device-independent - it can be used with any image, with any properly color-managed software,
without regard for where the image originated.
Fifth, above I have used the words translate and translation as a descriptive metaphor for what
lcms does when it translates RGB values from one color space to another via the PCS. The usual
and correct terminology is convert and conversion, which I will use below. The four methods
of conversion from one color space to another are: perceptual, relative colorimetric, absolute
colorimetric, and saturation. Which method of conversion you should use for any given image
processing step from raw ﬁle to ﬁnal output image is beyond the scope of this tutorial. The
standard advice is: when in doubt, use perceptual.
Sixth (and again, strictly for future reference), assign a proﬁle means change the meaning of
the RGB numbers in an image by embedding a new proﬁle without changing the actual RGB
numbers associated with each pixel in the image; convert means embed a new proﬁle, but also
change the RGB numbers at the same time so that the meaning of the RGB values - that is, the
real-world visible color represented by the trio of RGB numbers associated with each pixel in
an image - remains the same before and after the conversion from one space to another. You
should be able to do multiple conversions of an image from one working space to another, and
with a properly color-managed image editor, even though all the RGB numbers in the image
will change with each conversion, the image on your screen should look the same (leaving aside
the usually unnoticeable small but inevitable changes from accumulated gamut mismatches and
mathematical rounding errors). However, every time you assign a new working space proﬁle
rather than convert to a new working space, the appearance of the image should more or less
drastically change (usually for the worse).
Finally, (and this is a crucially important point), color management is NOT only relevant if you
shoot raw. Color management affects every stage of the image processing pipeline, whether you
start with a raw ﬁle that you, yourself interpolate and translate into a tiff, or if you start with a
jpeg or tiff produced by your camera.
Copyrighted and copyleft working spaces:
Iwill take it as given that ALL the ordinarily encountered working spaces, such as:
1. the several variants of sRGB (seecolor.org)
3. the various ECI (European color initiative) working spaceproﬁles
4. AdobeRGB, Adobe WideGamutRGB, and Kodak/Adobe ProPhotoRGB (Kodak and Adobe
ProPhoto are the same, just branded differently) and theirnon-branded,non-copyrighted
counterparts (Oyranos includes a non-branded version of AdobeRGB
5. andquite afew othersthat couldbe added to thislist are allmore or lesssuitable asworking
spaces. Which working space you should use depends only and solely on YOU, on YOUR
requirements as the editor of YOUR digital images with YOUR eventual output intentions
(web, ﬁne art print, etc).
However, as a critical aside, if you are using Adobe (or other copyrighted) working space pro-
ﬁles, these proﬁles contain copyright information that shows up in your image exif information.
Lately I’ve been perusing the openicc mailing lists. Apparently lcms can be used to produce non-
branded, copyleft working space proﬁles that are just the same as - actually indistinguishable
from - the branded, copyrighted working space proﬁles. It would be a wonderful addition to
digikam if a set of ´´copyleft´´ working space proﬁles, including nonbranded, relabelled versions
of ProPhotoRGB, AdobeRGB, and Adobe WidegamutRGB (perhaps in two ﬂavors each: linear
gamma and the usual gamma), could be bundled as part of the Showfoto package.