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Basic Processing
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Over-exposure can ruin any digital shot, so the camera
makers bias the exposure to give the shooter a bit of headroom,
causing lower contrast subjects to look a bit dull and flat.
This is a good thing.
Never work on an original image
direct from the camera. It is well to keep a duplicate folder
of your work on a partition separate from the image extracted
from your camera. Work on these, leaving the originals intact.
Back up to CD-ROM or tape frequently. As you grow in skill,
you may want to go back to early images and reprocess them.
If you have saved over the original images, there is no
way to go back.
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Levels
Since Levels will be used for almost every digital image,
it is well to learn the key combination - Ctrl+L.
When Levels is called, it makes a graph of how the data
is distributed between the darkest and the lightest. It
is called a histogram.
The histogram on the left does not touch either margin,
meaning that all the data the camera could gather from the
scene is there. Since the bulk of the data is toward the
left, the image appears dark.
The triangles below the histogram can be moved to indicate
where you want black and where you want white. We will do
this next step below.
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Setting Highlights and Shadows
Each photograph has a unique histogram, but most will
resemble the one on the left. If the mass rests against
the left side of the graph, it indicates under-exposure
and some shadow detail will be lost. If it is piled against
the right, highlight detail is lost.
Usually we want a little bit of pure black without detail
and a bit of pure white - also without detail. The left
triangle is moved just enough to assure the little bit of
black, and the right triangle is just clipping the white
side.
This feature is interactive, and when you move the cutoff
points, you will see the change as long as "Preview"
is checked.
Click on OK.
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Adjusting Middle Tones - Gamma
In the previous step, we set the highlights and shadows where
we wanted them, but the image still looked dark. Clipping more
of the histogram with the white triangle would certainly lighten
the image, but it would also throw away highlight detail.
The middle triangle adjusts mid-tones without impacting highlight
or shadow detail. Since the image was biased toward dark, it was
opened up by moving the triangle to the left until it began to
look washed out. Then the triangle was moved back just enough
to make the picture rich looking again.
Watch the preview as you move the triangle. The gamma step is
done entirely visually.
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Saturation
If the image is still looking a bit flat or anemic, a bit of
saturation can make it sing though all images do not require it.
The key combination for saturation is Control+U.
While a little saturation is a good thing in many cases, a lot
of saturation is not unless you are working on a special effect.
Again it is interactive. Watch the image on the screen as you
add it.
Hue and lightness have considerable utility, but we will skip
them for now. However, do pull the sliders if you are curious.
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Sharpening
Interestingly, an unsharp mask yields sharpening in photography!
Again this is an optional step, and one that may not be needed
on every shot.
It is interactive, and again one can use to preview to decide
how much one wants to use.
In many cases these few steps will give fine results and nothing
more need be done.
Next we will deal with an image shot under incandescent lights
with the white balance set on daylight. Colour correction!
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