How a Digital Camera Works.gif)
A digital camera
works a lot differently than a traditional 35mm camera. For
those of you who are new to the world of digital cameras,
the following is a breakdown on how digital cameras work.
You may also want to read our Buyers Guide to Shopping for
a Digital Camera if you need help on deciding what type of
digital camera to purchase.
Basics of a Digital
Camera
A digital camera
captures an image through a sensor called a CCD. This sensor
has light sensing dots called pixels. The actual resolution
of a camera is the total number of pixels that are located
on the CCD sensor. Resolutions of digital cameras range from
(0.3 megapixels to 5+ megapixels). A megapixel is just a way
of expressing how many pixels are on the CCD sensor, in millions.
Thus, a 2-megapixel camera has 2 million pixels on the cameras
CCD sensor.
The more pixels
a digital camera has on its CCD sensor, the larger the pictures
you can take. The following is a list of the maximum size
an image may be (measured by height x width) for the three
most popular types of digital cameras on the market today.
- 2-megapixel
digital cameras - 1600x1200
- 3-megapixel
digital cameras - 2048x1536
- 4-megapixel
digital cameras - 2272 x 1704
It needs to be noted that the amount of megapixels on a digital
camera is not part of the equation in factoring in image quality.
For example, take two identical digital cameras, 1 of which
is a 1-megapixel camera and the other is a 3-megapixel camera.
The picture quality produced by these cameras will be identical
except that the 3-megapixel camera will produce a larger image.
Of course, this
example really does not hold true with reality. Why? As
a
broad, general rule, 2-megapixel cameras tend to take higher
quality pictures than do 1-megapixel cameras due to better
construction, better lenses, better sensors and more built-in
functions to deal with difficult photography conditions.
Likewise,
a 3-megapixel camera tends to produce images that are slightly
better in quality than a 2-megapixel camera.
Storage of Images
on a Digital Camera
A digital camera
stores all of the pictures it takes on a memory card. The
most common type of memory card is the compact flash card
(CF Card). Some newer types of cards (such as the SmartMedia
cards) for specialized cameras have recently been introduced
as well, although the standard CF Card is by far the most
popular and least expensive.
A memory card is
measured by its memory size, in megabytes (MB). The more memory
the card has the more images it can hold. Thus, a 256 MB memory
card will be able to hold many more images than a 32 MB memory
card.
How many images
can be fit onto a particular memory card varies greatly. The
amount of images a memory card will hold depends on the factors
listed below:
As an important
side note, virtually all cameras on the market today come
with an introductory memory card of either 8 MB to 32 MB.
Plan on purchasing additional memory cards when you buy
a
digital camera.
Compression
Compression is
how much the digital camera compresses an image. When a digital
camera takes a picture, a very large file is created that
holds the image. In fact, a picture produced from a 2-megapixel
camera will produce a file size around 6MB - which is a very
large file indeed. In order to fit more images on a memory
card, digital cameras compress these image files. The amount
of compression a digital camera does to an image can usually
be set by the user. Standard compression modes on digital
cameras usually include either:
- Good, Better,
Best or...
- Normal, Fine,
Superfine
For most digital
cameras, the default will be either "better" or
"fine". While the amount of compression a camera
does will vary from camera to camera, generally a "good/normal"
compression setting will compress an image at a ratio of 16:1.
A "better/fine" setting will compress an image at
a ratio of 8:1. A "best/superfine" setting will
compress an image at a ratio of 4:1. The higher the compression
ratio is, the more images may be fit onto the memory card.
Using these generalized
numbers, you can see that having a "good/normal"
compression setting allows you fit many more images on a memory
card. However, when an image is compressed, detail is lost
of the image. The more compression you do to an image, the
less detail will be found on the image. Highly compressed
images can also come out looking fuzzy and blocky at times,
too.
For this reason,
most digital cameras come with a default setting of "better/fine".
It has been my experience with my Canon A40 that unless you
plan on printing out images or need very high definition photographs,
the "better/fine" setting works extremely well while
still allowing you to put lots of images on the memory card.
Resolution
As mentioned earlier,
resolution is how many megapixels are on a CCD sensor in the
digital camera. On most digital cameras, you can change the
resolution. For example, a 2-megapixel camera can take images
up to 1600x1200, which is a sizable image and one that creates
a large file. If you do not want an image of this large size,
you can change the resolution setting on the camera to make
the image smaller (this will not effect the quality of the
image, only its size). The smaller image size will have a
smaller file size, allowing for more images to be placed on
the memory card.
For example, most
2-megapixel cameras can take pictures at the following resolutions:
1600x1200, 1024x768 and 640x480.
Photographic Conditions
The type of picture
you take can also play a small role in how many images can
ultimately be stored on a memory card. I've found that daylight
pictures that are highly colorful tend to have a larger file
size than do images that are duller in color or have been
taken at night. The difference in file sizes is not huge,
but photographic conditions do effect to a small degree how
many images may be fit onto a memory card.
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