The image sensor we looked at in the previous illustration
is based on a common design used in most digital
cameras. But there are exceptions to the layout of the
light receptors for the different colors. And once the
photodiodes, in any configuration, have gathered their
information, there are differences in how that information
is turned into digital data that the camera’s microproces-
sor can tweak before storing it on a memory card. Here
are the most important exceptions to the rule.How the Fuji SR Sensor
Has Double Vision
The ultimate challenge for photographers is to
capture the greatest dynamic range in their pho-
tographs.Dynamic rangeis the ratio of the
highest non-white value and smallest non-black
value. More simply, it means that details are
easily discernable in the lightest and darkest
portions of the photograph. In this picture, there
is enough light to delineate the granules of dark
soil but not so much light as to burn out the details on the highlighted portions of the leaves.The photos to the left show how adjusting
exposure can’t always compensate for an
image sensor’s poor dynamic range. If you
increase exposure to show the details in the
shadows of the lighthouse, the colors in the
sunset wash out. If you decrease exposure to
capture saturated colors in the clouds, the
lighthouse details are lost in the shadows.2
In digital photography, the size of the photodiodes influences dynamic range.
Think of the diodes as buckets catching rain. A photodiode that is full is pure
white. If the photodiodes are too small, the rain overflows and floods adjacent
buckets so they are all full, resulting in something called blooming—a patch
of full photodiodes that produces a white area with no detail. If the buckets
are too big and there’s little rain, the water might not even cover the bottoms
of the pails, and there’s nothing to measure. In photodiodes, that amounts to a
part of a photograph being completely black, without the relief of any details.3
1
How Image Sensors Differ
(^104) PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES