Pentax Optio W90 Operating Manual page 36

Histogram
A histogram shows the
brightness distribution of an
image. The horizontal axis
represents brightness (dark at
the left and bright at the right)
and the vertical axis
represents the number of
pixels.
←Brightness→
(Dark) (Bright)
The shape of the histogram
Dark portions Bright portions
before and after shooting tells
you whether the brightness and contrast are correct or not, and lets you
decide if you need to use EV compensation and take the picture again.
Setting the Exposure (EV Compensation) 1p.133
Understanding Brightness
If the brightness is correct, the graph peaks in the middle. If the image is
too dark, the peak is on the left side, and if it is too bright, the peak is on
the right side.
Dark image Correct image Bright image
When the image is too dark, the part to the left is cut off (dark portions)
and when the image is too bright, the part to the right is cut off (bright
portions).
The Optio W90 has a function where bright portions are indicated as
blinking red and dark portions as blinking yellow.
Understanding Contrast
The graph peaks gradually for images in which contrast is balanced. The
graph peaks on both sides but sinks in the middle for images with a large
difference in contrast and low amounts of mid-level brightness.
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