How a Digital Camera Works
By: Paul Lines
 Digital
cameras operate much the same as classic cameras.
Both camera types need to have a lens with which to
focus on the image, a shutter with which to let
light into the camera and an aperture with which to
adjust the amount of light that comes into the
camera.
Traditional and digital photography differ once the
light comes into the camera. The traditional camera
will capture the image on a film. The digital camera
will capture the image on a device that is called an
image sensor.
The image sensor is an electronic device that is
composed of electrodes (also known as photosites).
These electrodes measure the intensity of the light.
The CCD (charge coupled device) is the most common
image sensor available. Other sensors include the
CMOS and the Foveon.
The digital camera gets its megapixel (also known as
millions of pixels) rating from the number of
photosites the image sensor has. Every photosite is
connected to a pixel in the final photo. This means
that a camera that has 6 megapixels will have an
image sensor that is 3008 pixels in width by 2000
pixels in height.
The light that connects with the image sensor will
be changed into electrical signals. These signals
are then amplified and moved to an A/D (analog to
digital) converter. This A/D converter will change
the signals into binary numbers. These binary
numbers are then computed by a computer that is
inside the body of the camera. After the numbers
have been converted the image result will be saved
on a memory card.
Photosites will only measure light intensity. They
won't measure color. If you want to create a color
image each and every photosite will need to be
covered by a filter which is colored. The colors
will be green, blue, or red, which are the three
primary colors. These primary colors can be blended
to create all other colors including the color
white.
These colored filters are then placed on a grid.
There will be twice as many green colored filters as
there will be blue or red. The reason for this is
that your eye is doubly as sensitive to light that
is green. The filters will be arranged in what is
called a "Bayer" pattern. There will be one row of
red, one row of green, one row of red (etc). This is
followed by a pattern of blue, green, blue, green,
etc.
 Remember
that every photosite can only be used with one
colored filter. This means that you need to use
computer processing to create an image that has a
full color range. Every pixel will be analyzed and a
composite color will be produced after they have all
been calculated. If a red pixel is in the middle of
green and blue pixels, the red pixel will actually
be white. This is because white is what you get when
you combine red, blue, and green. The name for this
process is "demosaicing".
Once the demosaicing is complete the image will be
adjusted to match your camera settings. Most digital
cameras will have adjustable settings for contrast,
brightness, and color saturation. Once you make the
adjustments many cameras will also add an algorithm
for sharpening to make the image even clearer.
The last step before you store the image onto the
memory card is "compression". Most digital cameras
will use what is called a JPEG format for
compression. The compression process reduces the
file size by getting rid of extra data. The data can
not be recovered, therefore the JPEG process is
called a "lossy" format.
Most digital cameras will allow you to save any
uncompressed images as TIFF files, also known as raw
data. The raw data is what the photosite data was
before the demosaicing process. The TIFF files can
be transferred to your computer where you can use
software to process it with most of the same
functions as the camera only with much more control.
Paul Lines is a teacher and has a keen interest in
digital photography. His free online photography
tips are viewable at
http://www.digitalphotographytraining.net. Visit
his page to learn new techniques in Digital
Photography.
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