ChApter 1. digitAl CAmerAs & imAges
32 For more on textbooks in digitAl photogrAphy, visit http://www.photoCourse.Com
http://www.photocourse.com/itext/pixels/pixels.pdf
http://www.photocourse.com/itext/pixelzoom/
contrast, and brightness are more effective on larger images because there
is more image data to work with. After making these adjustments, you can
reduce the file to the needed size.
As you might expect, all else being equal, costs rise as the size of the image
sensor increases. Although larger sensors can give you sharper images and
better enlargements, more pixels also means larger image files. Not only do
larger files take up more storage space, they take longer to transfer, process,
and edit and are often far too large to e-mail or post on a Web site. Smaller
image sizes such as 800 x 600 are perfect for Web publishing, e-mail attach-
ments, small prints, or as illustrations in your own documents and presen-
tations. For these uses, higher resolutions just increase file sizes without
significantly improving the images.ChooSing imAge SizeS
The camera you use determines how large your images can be, but most also
allow you to select smaller sizes. Here are some rules of thumb about what
image sizes you need for certain outputs.- On the Internet, images are displayed on screens that have resolutions of
1280 x 1024, 1152 x 864, 1024 x 768, 800 x 600, or 640 x 480. A few years
ago, a 1024 x 768 monitor was unusual so most people in the industry settled
on assuming that the lowest common denominator for screen sizes was 640
x 480 or, at best 800 x 600. For this reason, images to be e-mailed or posted
on the Internet should be of similar or smaller sizes—no more than 800 pix-
els wide. This ensures that the images will display correctly on the vast ma-
jority of computers. If an image is too large, users will not be able to see it all
at once and will be forced to scroll around it. If too small, details will be lost.
Size also affects the speed with which images travel over the Web. Smaller
(and more compressed) images travel faster so people see them more quickly. - For laser and inkjet printers you need between 200–300 image pixels
per inch. If your camera can capture images that are 2400 pixels wide, you
can expect good results when prints are up to 12 inches wide. - When images are printed on a printing press, as they might be for a
catalog, the pixels in the image are printed as dots on the page. Photographs
One advantage of a
large image size is that
it gives you the freedom
to crop the image and
still have it be a usable
size.
When a digital image
is displayed or printed
at the correct size for
the number of pixels
it contains (left), it
looks like a normal
photograph. When
enlarged too much
(right), its square pixels
begin to show.
Click here for a PDF
extension on pixels
and read Part 2 on
displaying images
and Part 3 on printing
images.
Click to see the effects
of pixelization as an
image is enlarged.