For more on digitAl photogrAphy, visit http://www.shortCourses.Com 2 http://www.photocourse.com/itext/exposure/
image sensors—introduction...
Digital cameras have roots going back almost 200 years. Beginning with the
very first camera all have been basically black boxes with a lens to focus the
image, an aperture that determines how bright the light is, and a shutter that
determines how long the light enters. The big difference between traditional
film cameras and digital cameras is how they capture the image. Instead of
film, digital cameras use a solid-state device called an image sensor. In some
digital cameras the image sensor is a charge-coupled device (CCD), while
in others it’s a CMOS sensor. Both types can give very good results. On the
surface of these fingernail-sized silicon chips are millions of photosensitive
diodes, each of which captures a single pixel in the photograph to be.An image sensor sits
against a background
enlargement of its
square pixels, each
capable of capturing
one pixel in the final
image. Courtesy of IBM.When you take a picture, the camera’s shutter opens briefly and each pixel
on the image sensor records the brightness of the light that falls on it by
accumulating photons. The more light that hits a pixel, the more photons it
records. Pixels capturing light from highlights in the scene will have many
photons. Those capturing light from shadows will have few.
After the shutter closes to end the exposure, the photons from each pixel are
counted and converted into a digital number. This series of numbers is then
used to reconstruct the image by setting the color and brightness of matching
pixels on the screen or printed page.Click to explore howUnderstanding Exposure
how light or dark an
image is.A CCD is like a three-
decker sandwich. The
bottom layer contains
the photosites. Above
them is a layer of
colored filters that
determines which color
each site records.
Finally, the top layer
contains microlenses
that gather light.
Courtesy of Fujifilm.imAge sensors—introduCtion