How digital cameras work
The Exposure
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, usually a charge-couple device (CCD). On the surface of
each of these.
fingernail-sized silicon chips is a grid containing hundreds of thousands or
millions of photosensitive diodes called photosites, photoelements, or pixels. Each
photosite captures a single pixel in the photograph to be.
How digital cameras work
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When you press the shutter release button of a digital camera, a metering
cell measures the light coming through the lens and sets the aperture and
shutter speed for the correct exposure. For a digital camera when the
shutter opens briefly, each pixel on the image sensor records the brightness
of the light .
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Pixels capturing light from highlights in the scene will have high charges.
Those capturing light from shadows will have low charges.
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When the shutter closes to end the exposure, the charge from each pixel is
measured and converted into a digital number. The series of numbers can
then be used to reconstruct the image by setting the color and brightness of
matching pixels on the screen or printed page.
How digital cameras work
How digital cameras work
What is color?
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It may be surprising, but pixels on an image sensor can only capture brightness, not
color. They record only the gray scale-a series of 256 increasingly darker tones
ranging from pure white to pure black. How the camera creates a color image from the
brightness recorded by each pixel is an interesting story.
Colors in a photographic image are usually based on the three primary colors red, green,
and blue (RGB). This is called the additive color system because when the three colors
are combined or added in equal quantities, they form white. This RGB system is used
whenever light is projected to form colors as it is on the display monitor (or in your
eye).
How digital cameras work
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Since daylight is made up of red, green, and
blue light, placing red, green, and blue filters
over individual pixels on the image sensor can
create color images.
On many image sensors, there are twice as
many green filters as there are red or blue
filters. That's because a human eye is more
sensitive to green than it is to the other two
colors so green's color accuracy is more
important.
Creating a color by mixing varying amounts of
other colors on this palette. This step is
computer intensive since comparisons with as
many as eight neighboring pixels is required to
perform this process properly.