The photograph below includes a lot of sky and therefore
the Buddhist statue (at Repulse Bay, Hong Kong) has come out
rather dark. You might be tempted to use the
Brightness/Contrast panel to improve the picture. Don't!
When you increase the brightness in this way, light is added
to every part of the picture, so you will find that parts of
the picture that should be pure black have become grey -
pure black is no longer available. Similarly, using the
Brightness control to make an overly-bright picture darker
would also be a mistake, for pure white would no longer be
present anywhere in your picture. In other words, the
Brightness control is always to be avoided!
There are two other, better and more sophisticated
alternatives for changing brightness. The first is to apply
a 'curve' to the picture and the second, as we saw in the
previous lesson, is to adjust the
'Levels'. Let's try the curve control first.
Choose Layer>Colors> Curves and make sure that
the Preview option is turned on. Notice that is already a point at each end of
the 'curve' - we will usually not touch these two points.
Use your mouse to drag the center of the diagonal line into
a new position, thus adding a third point, and note that it
is possible to brighten or darken the image without losing
the pure blacks and whites in the image. If you want to
play, you can try pulling more than one point on the line
(some very weird effects are possible), but if all you want
is a simple brightness correction then a single added
point should be enough (you can't get rid of
points that you have added except by resetting everything so
think twice before adding additional points).
If you're like me, you'll probably find the colors of the
statue are rather pale. To make them more intense or
'increase their saturation', choose
Layer>Colors>Hue-Saturation. As usual, make sure the
preview option is turned on. Don't be tempted to adjust the
brightness here, for the reasons we have already discussed.
This photo doesn't need a 'hue' (tint) adjustment, but try
it anyway to see what it does.
As you discovered in the previous lesson, the Levels
control can also be used to adjust brightness, mainly by
moving the middle triangle under the graph, but we could not
have used the Levels control to get the result we achieved
here i.e. brighten the statue without brightening the sky.
Thus it would seem that the Curves control is the best
control for adjusting brightness, nut don't forget that the
levels control has the advantage that it allows us to make
sure that our image is using the full range of brightness
possible, all the way from pure black to pure white.
Decreasing contrast
As promised in the previous lesson, I will
now suggest a good method for reducing the contrast when
necessary. As stated the previous lesson, the use of the contrast
control is not recommended for it will cause your picture to
lose any pure white or black that it contains, making the
picture look flat and lifeless. The better method is to use
the curves control introduced above.
Copy this picture (a tiny Japanese drinking
water fountain) to your folder.
Although the overall brightness is OK, the
high contrast makes the picture rather harsh and makes it
difficult to see detail in the leaves to the left of the
fountain. Open the picture in the GIMP and display the
curves control. To reduce contrast without
losing whites or blacks, make a four point curve like this:
The central part of the curve is less steep
than before, and it is this that corresponds to reduced
contrast. This picture doesn't need much adjustment so don't
overdo the correction. If you care to check with the level
control, you will find that the picture has not lost its
pure whites and blacks. Save your work.
It should be clear from this lesson that
these are powerful tools that are sometimes hard too use.
When you reach the Adjustment Layer lesson I will
show you how you can use the curves and levels controls in
such a way that you can easily return to them later to make
adjustments.
