| Histogram
Usually, after you have taken a picture, you can view it.
In your camera's menu you can view the histogram and see how the exposure
turned out. Also, in PhotoShop, you can
review histograms for all your pictures. The 'perfectly exposed' image is
one where the histogram makes a near perfect bell curve, similar to the one
below.

However, I've found that in reality, it can
be ok if the 'bell shape' is skewed rather narrow and at one end. What you
need to know is,
especially since it's easy to 'blow out the highlights' with digital, is if
there's too much light information being gathered by the photocells on the
sensor. If there's too much, then that'll be represented by the appearance
of a flat top (see figure below). That means that there's more light
information available, and so all the details of like textures and shadows
can be lost, resulting in highlights.

If you do have images with flat tops, then
you'd say that these images have blown-out highlights; that is, the bright
areas are too bright, so they lack colour information, and you see only
white, and no texture as well. This is not ideal. The other thing is you cannot retrieve this information in PhotoShop. The
Photocells were overloaded, and so the opportunity is gone.
What you would do in this situation is either
increase the shutter speed, close the aperture a bit, add a
Neutral Density filter, or reduce
the iso to something closer to 100 or 80 (or whatever the lowest you can set
your camera to).
Usually, when you push the green arrow button
on your camera, immediately after taking a photo, you should be able to push
something else so you can view both the image and its histogram. Look it up
in your camera's owner's manual. |