137. Improve Brightness and Contrast
Before You Begin
136 About an Images Histogram
See Also
138 Improve a Dull, Flat Photo
If you grew up using a television set that had an old style of operating control called
knobs
, you'll recall there were two such gadgets,
generally
labeled
Brightness
and
Contrast
. And if you ever
played
with these knobs as a childand survived with your wrists unscathedyou remember that Brightness made your picture
whiter
while Contrast made the blacks and whites in your picture stand out.
With all due respect to Philco-Ford, Admiral, Magnavox, and the other great manufacturers of the past century, I'm going to show you here how to use Photoshop Elements' equivalent of the Brightness and Contrast knobs. And then I'm going to rap you on the wrists if you use them too much. Actually, I'm not kidding this time: Although it does help in some circumstances to restore a more natural appearance to an image, the
Brightness/Contrast
command, when used too liberally, can result in a washed-out look (too bright), a washed-
down
look (too dark), or an
underexposed
look (too much contrast). More importantly, because pixels cannot have a brightness value of greater than 255 or less than 0, when you
brighten
or
darken
pixels
too much
, you lose the distinguishing contrasts between the brightest or darkest pixels among them. Then when you try to get those contrasts back with a
Levels
adjustment, you can't. With the technique demonstrated here, you can use the
Brightness/Contrast
command effectively and safely, without losing information in your image.
NOTE
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With the
Brightness/Contrast
command, brightness is added to an image (or to a layer or selection) by adding equal amounts to, or subtracting from, the
Brightness
component of
every pixel in the image
. So, although you might be restoring the natural brightness level of the midtones, natural darks might be washed out. By comparison, a contrast adjustment mathematically
redistributes
brightness across the entire image, flattening the image's
histogram
and reducing its peaks. However, the same danger of losing bright and dark values remains valid with contrast adjustment, except on both sides of the histogram instead of one.
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1.
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Choose Enhance, Adjust Lighting, Brightness/Contrast
Open
the image you want to adjust in the
Editor
in
Standard Edit
mode and save it in Photoshop (
*.psd
) format. To display the
histogram
palette
if it is not already showing, select
Window, Histogram
. From the palette's
Channel
drop-down list, choose
RGB
. If there is more than one layer in the image, choose the layer you want to adjust in the
Layers
palette. If you want to limit your adjustment to a region of the image, use a selection tool to select that region. See
70 About Making Selections
for an explanation.
Choose
Enhance, Adjust Lighting, Brightness/Contrast
from the menu bar. The
Brightness/Contrast
dialog box opens. Enable the
Preview
check box so that you can see the results of the adjustments you're making in the actual image.
In this example, the photo was taken at dusk without a flash. Although it does capture the moment, it's the worst time of day to take a digital photo for many
cameras
. If the flash had been turned on, the subject would have been well lit, but the sky would no longer be a dreamy blue but a dreary clay color. My goal here, for now, is to make the subject matter clearly visible while losing as little of the original
color
scheme as possible.
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2.
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Adjust Brightness or Contrast
To add brightness value to all the pixels in the designated region, slide the
Brightness
slider to the right, or enter a positive value in the
Brightness
text box. To reduce brightness in all the pixels in the designated region, slide the
Brightness
slider to the left, or enter a negative value in the
Brightness text
box.
To add contrast between pixels in the designated region (making light pixels lighter and darks
darker
), slide the
Contrast
slider to the right, or enter a positive value in the
Contrast
text box. To reduce contrast between pixels in the designated region (bringing all brightness values together toward a middle gray tone), slide the
Contrast
slider to the left, or enter a negative value in the
Contrast
text box.
NOTE
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As you increase contrast for an image, you might notice that the black curve in the
Histogram
palette has "teeth" in itspecifically, evenly
spaced
vertical
stripes
. This is natural, and is an accurate depiction of the brightness values in an adjusted image. For the sake of argument, suppose that there were only 10 levels of brightness in a given image,
ranging
in value from 10 to 20. After the adjustment, suppose that they now ranged in value from 5 to 25. Because all pixels were adjustednone are left behind
there are still only 10 levels of brightness
. They've just been broken up, such that there are pixels with brightness of 5, 7, 9, and so on, but none with 6, 8, 10, and so on. Notice in the example how the contrast-adjusted image looks spotty,
noisy
, and unsmooth. What your eyes see is
verified
by the "teeth" in the contrast-adjusted histogram.
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As you make adjustments, notice the instant change to the
Histogram
palette. The gray curve with the bright tip represents the image's existing
histogram
; the black curve represents the adjusted state as you see it in the preview. With a brightness change, the entire "mountain" of the graph shifts to the left or right. With a contrast change, the entire "mountain" is flattened, as if eroded by a
rising
tide. While you're making these changes, watch the
Histogram
palette, being mindful of two things:
-
Don't adjust the image so much that pixels on either or both sides of the histogram fall off the edge. When that happens, you're losing
vital
information which, when saved, cannot be retrieved.
-
In the interest of restoring one of the image's qualities to a natural or pleasing appearancefor example, distinguishing a little girl from her picnic basketdon't introduce negative qualities on the
opposite
end of the scale, such as a washed-out tone for the grass, or water that appears to glow as if it were emanating from a
nuclear
facility.
To finalize your adjustments, click
OK
.
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3.
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View the Result
TIP
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If you press the
Alt
key on your keyboard, the
Cancel
button changes to read
Reset
. Click that button to erase your changes to the image, leaving the dialog box open so that you can try again.
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In the example, after adding
+30
to brightness and
+20
to contrast, the range of color now looks more natural. But the image has far to go before it's fixed. In the adjustment, I did lose some of the distinguishing bright values along the right side of the
histogram
, although not many.
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