ChApter 3. Controlling exposure
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Most scenes contain a continuous spectrum of tones, ranging from pure black
at one end to pure white at the other—the gray scale. When shooting JPEGs
there are 256 tones in the scale (2^8 ) and when shooting RAW images there
are up to 65,536 (2^16 ). The tone in the middle of these ranges is middle gray
and reflects exactly 18% of the light falling on it.The gray scale captured
in an image is a range
of tones from pure black
to pure white.
When you photograph a subject, your camera’s autoexposure system sets the
exposure so the average brightness in the image is middle gray regardless
of the scene’s actual brightness. As a result, when you photograph a scene
with an average brightness lighter or darker than middle gray, the image will
be darker or lighter than the scene. For example, if you photograph a white
card, a gray card, and a black card, and each completely fills the viewfinder
when the exposure is calculated, each of the cards will be middle gray in the
captured image.Because of the way your
exposure system works,
if you photograph a
white card, a gray card,
and a black card (top
row), the exposure
system sets the camera
to capture each as
middle gray (bottom
row).
To realistically capture a scene that doesn’t average out to middle gray, you
have to use exposure compensation or some other form of exposure control
to lighten or darken the picture.how your meter works