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The Showfoto Handbook
tonal response curve instead of a gamma value - seeherefor more information, and then google
around for more in-depth information.
In addition to gamma 1.8 and gamma 2.2 the only other gamma for a working space that gets
muchmentionor use isgamma1.0, also called linear gamma. Linear gammais used in HDR (high
dynamic range) imaging and also if one wants to avoid introducing gamma-induced errors into
one’s regular low dynamic range editing. Gamma-induced errors is a topic outside the scope of
this tutorial, but seeGammaerrorsinpicturescaling,for gamma-induced color shifts.
Unfortunately and despite their undeniable mathematical advantages, linear gamma working
spaceshave so few tones in the shadowsthat (in my opinion) they are impossible to use for edit-
ing if one is working in 8-bits, and still problematic at 16-bits. When the day comes when we are
all doing our editing on 32-bit files produced by our HDR cameras on our personal supercom-
puters, I predict that we will all be using working spaces with gamma 1; Adobe Lightroom is
already using a linear gamma working space ´´under the hood´´ and Lightzone has always used
alinear gamma working space.
Which working space: large gamut or small gamut
One MAJOR consideration in choosing a working space is that some working spaces are bigger
than others, meaning they cover more of the visible spectrum (and perhaps even include some
imaginary colors - mathematical constructs that don’t really exist). These bigger spaces offer the
advantage of allowing you to keep all the colors captured by your camera and preserved by the
lcms conversion from your camera profile to the really big profile connection space.
But keeping all the possible colorscomes at aprice. It seems that any givendigital image(pictures
of daffodils with saturated yellows being one common exception) likely only contains a small
subset of all the possible visible colors that your camera is capable of capturing. This small
subset is easily contained in one of the smaller working spaces. Using a very large working
space mean that editing your image (applying curves, saturation, etc) can easily produce colors
that your eventual output device (printer, monitor) simply cannot display. So the conversion
from your working space to your output device space (say your printer) will have to remap the
out of gamut colors in your edited image, some of which might even be totally imaginary, to
your printer color space with its much smaller gamut, leading to inaccurate colors at best and at
worst to banding (posterization - gaps in what should be a smooth color transition, say, across
an expanse of blue sky) and clipping (your carefully crafted muted transitions across delicate
shades of red, for example, might get remapped to a solid block of dull red after conversion to
your printer’s color space).
In other words, large gamut working spaces, improperly handled, can lead to lost information
on output. Small gamut working spaces can clip information on input. Like Wikipedia says, it’s
atrade-off. Here is some oft-repeated advice:
1. For images intended for the web, use (one of the) sRGB (variants - there are several).
2. For the most accuracy in your image editing (that is, making the most of your ´´bits´´ with
the least risk of banding or clipping when you convert your image from your working
space to an output space), use the smallest working space that includes all the colors in the
scene that youphotographed, plusa little extraroom for those new colors you intentionally
produce as you edit.
3. If you are working in 8-bits rather than 16-bits, choose a smaller space rather than a larger
space.
4. For archival purposes, convert your raw file to a 16-bit tiff with a large gamut working
space to avoid loosing color information. Then convert this archival tiff to your working
space of choice (saving the converted working tiff under a new name, of course). Seehere
for more details.
The WHYs of these bits of advice regarding which working space are beyond the scope of this
tutorial. See Bruce Lindbloom’s excellent website (Info,InformationaboutRGBWorkingSpaces)
for a visual comparison of the gamut (array of included colors) of the various working color
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