How
does a digital camera work?
by Digital Darrell
username: DigitalDarrell
Nikonian in Tennessee, USA
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OPERATION
The operation of a digital camera, from the
standpoint of the user, is virtually the same as the operation
of a 35mm camera. Most digital cameras imitate their older
film cousins very well, so a new digital user has little to
fear in the operation of the camera.
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| Nikon
2 Megapixel Coolpix 2500 and the 4 Megapixel Coolpix
4500 |
If you are used
to a point-and-shoot, or even an SLR (single lens reflex)
35mm camera, then you will be able to find a digital camera
to meet your experience level. If you stay within the same
brand of cameras as your current 35mm, you will find that
the digital cameras of that manufacturer work about the same
as their film cameras.
The biggest difference in the operation of
the camera is in the storage medium, and number of images
made between changes. For instance, with a 35mm camera, you
can have a maximum of about 36 exposures before you have to
rewind the film, open the back, and insert another film roll.
With digital you might be able to shoot hundreds of images
before changing your "digital film". Most digital
cameras use a small memory card that inserts into a slot in
the camera body. Usually it will be behind a small door on
the side or bottom of the camera. The camera manual will explain
the process well enough to get started.
HOW IS THE IMAGE STORED?
(or what is a megapixel?)
When you take a picture with a digital camera
the light strikes a digital sensor array, instead of a piece
of film. These digital sensors are computer "chips"
with names like CCD, CMOS, Foveon, or others. They take the
place of a piece of film that must be moved across the focal
plane of the camera. The digital sensor is made of millions
of tiny sensor points called "pixels," which is
short for "picture elements." They are laid out
in an array with rows and columns, like in a computer spreadsheet
or wall calendar. For instance, my camera has an array of
sensors in its CCD that is 3008 horizontally, and 2000 pixels
vertically (3008x2000). If you do a simple mathematical formula
on the pixel array size you will come up with the "Megapixel"
rating of the camera. This is the number that most manufacturers
use to sell the camera. The simple formula 3008x2000 = 6,016,000
shows that my camera has over six million pixels, or is a
"six megapixel" camera.
Think
of megapixels as millions of dots of light that are
being stored for each picture. The more dots of light
there are, the higher the resolution of the image. More
pixel dots = bigger pictures. Usually, the more megapixels
the better! It takes a lot of megapixels to make prints
on photo paper, so it would be best to get a camera
with as many megapixels as you can afford. |
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When
the image strikes the sensor, it gets all those megapixels
excited. First the image goes through color filters above
the individual sensors. The sensor converts the image from
light waves into an analog electrical signal. The analog signal
is then run through an analog to digital converter (A-D Converter),
where it becomes a pure digital signal. Then it is again put
through a series of electronic filters that adjust the white
balance, color, and aliasing of the image. Next a compression
cycle makes the image as small as possible by dumping unnecessary
pixels, for more efficient storage. Now the camera has a nice
compressed, filtered, digital signal representing your image.
The
image is then transferred into a temporary storage area inside
the camera called "buffer memory," or simply the
"buffer." When the buffer is full, the image is
written out to your storage media, such as a memory card.
The buffer size in the camera is an important thing. It tells
how many images you can take in quick succession. If you have
a tiny buffer in your camera, you will have to wait a bit
after you take several images.
In
fact, the main thing that drives the cost up on digital cameras
is the number of megapixels, and the size of the memory buffer.
Most cameras have a reasonable amount of both, so you needn't
worry. Even if you can only afford a very inexpensive digital
camera, you will still have nice images, you just might be
limited in their maximum size on photo paper, and will have
to wait a bit when taking images quickly. Almost any digital
camera is capable of taking pictures for display on the Internet,
or for sending across the Internet as email. Images on the
Internet are very low resolution -- about 72 to 100 dots per
inch -- so any quality digital camera will be capable of making
beautiful images for display there.
WHAT ABOUT PRINTING MY DIGITAL IMAGES?
To
make a nice 4x6 inch print will require a camera of at least
two megapixels. To go up to an 8x10, or 11x14 inches, it is
best to have a four to six megapixel camera. Of course, an
image processor can make the smaller megapixel cameras do
larger prints by stretching the image a bit. This is a process
called "interpolation," which simply means adding
extra dots of light (pixels) to make the image larger. Image
quality degrades a bit when this happens, but is generally
acceptable. So a two-megapixel camera could make a print up
to 8x10 if needed. A four or six megapixel camera will do
an even sharper image, and can make nice images printed all
the way up to at least 11x14 inches.
One
nice feature that has not yet arrived on film cameras, other
than Polaroids, is the freedom to immediately view the image
you just took. Since even low-cost digital cameras have small
video monitors on the back of the camera, you are able to
see if that image is a keeper, or should be deleted. Think
of how much money you will save by only printing the images
you like, instead of taking a bunch of film images, keeping
the best ones, and shoving the rest in a shoebox in the closet.
Digital cameras cost more up front, but cost less over the
long run to use. You can afford to take many more pictures
than you ever could before using a digital camera.
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