Digital Images
Digital cameras capture images in bitmapped formats such
as JPG, PNG, TIFF or other internal formats (sometimes called
RAW).
How Good a Picture Will My Digital Camera Take?
In general, the more pixels you have and the less you
compress the image in storage, the better the image quality
will be. But, for most uses you do not need the biggest image
and the least compression.
How Many Pixels?
Digital cameras are currently marketed by the size of the
images they can take (for example, 3.2 Megapixels).
- The size is usually the file size of the largest
uncompressed image the camera can take.
- Cameras usually offer a range of other sizes. You can
select the size you want to shoot a particular picture
at.
- The more pixels in the picture, the bigger the image
file will be, although you will also be able to choose the
degree of compression at which the want the image
stored.
|
Image Dimensions in Pixels
|
Total Number of Pixels in Image
|
Image Size in Megapixels
|
Display Size at 72 Pixels Per Inch (on Web
page)
|
Print Size at 300 Pixels Per Inch (from high
quality printer)
|
|
640 x 480
|
307,200
|
.3
|
8.0in x 6.6in
|
2.1in x 1.6in
|
|
1600 x 1200
|
1,920,000
|
1.8
|
22.2in x 16.6in
|
5.3in x 4.0in
|
|
2400 x 1800
|
4,320,000
|
4.2
|
33.3in x 25.0in
|
8.0in x 6.0in
|
|
3200 x 2400
|
7,680,000
|
7.5
|
44.3in x 33.3in
|
10.6in x 8.0in
|
How Much Compression?
In addition to selecting the image size, you usually can
select the degree of compression of each image when it is
stored. This is often expressed as the level of "image
quality" (High, Medium, Low) that you prefer. The
relationship between image compression and quality results
from the fact that the compression method used is "lossey" -
the more the image is compressed, the more information is
lost. A highly compressed cannot be uncompressed back to its
original level of quality - in the compression process some
of the image detail was thrown away.
However, even when images are stored at high compressions,
they often uncompress at quite acceptable levels of quality.
You need to try the various combinations of image size and
compression to find the combination that is right for your
purposes.
