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Adjusting Curves
After making the adjustments to an image with Levels there still may be some
fine tuning necessary. Curves gives you quite a bit of control over the
brightness of different areas of the picture. If you need to darken the
background while keeping the brightness of faint areas unchanged, using the
Curves command is ideal. Curves is also perfect for increasing the
brightness of the midtones in an image while keeping the background dark and the
highlights from washing out. This can add a lot of punch to an image.
Below is our Whirlpool Galaxy image, after Levels and Color Balance and
Saturation adjustments.
Perhaps we still want a bit more punch to the image. Curves will allow
you to bring out the fainter parts of the galaxy while retaining a dark
background and while not making the core appear too overexposed.
Select Image > Adjust > Curves (or press Ctrl-M)
to open the Curves window. You will see a graph with a straight line
running diagonally from the lower left corner to the upper right corner.
The line plots input values versus output values. Bringing the bottom left
part of the line up increases the brightness of the darker areas of the image.
Bringing the center of the line up will increase the brightness of the middle
parts of the image, although since the whole line curves upward, all but the very
darkest and brightest pixels are affected.
An Example
To brighten the overall image, especially the middle ranges (where most of
the spiral arms structure lies), bring up the center of the Curves line.
Click on the line near the center of the graph and drag upward to create a
curve, as shown below:
The resulting image is brighter overall, but especially in the midtones.
When the curve is brought up, the bright regions become a bit too overexposed
and the background has become too light. Add another point on the curve
near the bottom left by clicking on the curve and drag the new point downward. This will darken the
background without changing the midtones. Then select a point on the top
right part of the curve and drag it back down to keep the bright core from
appearing too overexposed.
After all the Curves adjustments, the image appears as below:
Next, Cropping...
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