Datasheet

Exceptions to the high-resolution rule happen only when high resolution is absolutely
overkill for the purposes that you took the image in the first place. For example, if there
are some items that you want to put on eBay that don’t require a lot of magnification to
see product quality or details, then you may need just enough resolution to show that the
item is intact. Taking a full-resolution image may not be necessary, and large image down-
loads may annoy, rather than attract, potential buyers. If you are taking just a few images
of this sort, it may be just as easy to take the high-resolution image and resize the image
smaller later (especially if you find you have to look for the camera’s manual to figure out
how to change the resolution settings). Quality in this case is hardly the issue.
Images that you obtain using a scanner or scanning service fall into a similar category.
You will want to get as much detail as you can from a scan, but at some point you will be
examining the grain of the film or paper in the print rather than extracting detail from the
existing image. If you are scanning an image from a newspaper, you can use less resolution
(samples) than if you scan from a negative, because the resolution of newspaper printing
will be far lower (see Figure 1.2). The detail of your source can dictate the resolution as
well as the application.
If you are a casual shooter and only send photos to relatives via e-mail, keep in mind
that an image will display at about three times the size in a web browser (72 ppi) than it
does in print (240 ppi). So even resolution that seems low can be more than you really
need depending on what you do.
When going to print, too much image information can slow down processing and can
be overkill. If you have a 5
″ × 7″ image at 240 ppi, that will be enough to print at that size
for many purposes. That is just 1200 × 1680 pixels, roughly what you get from a 2 mega-
pixel camera. If you envision doing larger prints of the same quality, you will usually
need more resolution (depending on the output devices). On the other hand, using that
same image without resampling for a 2″×2.8″ image in a magazine is overboard: you’ll
have roughly twice the resolution you really need. That additional resolution taxes com-
puter imaging resources and will not improve your result. Imaging equipment ends up
just crunching the image information and decimating detail, likely using a simple averag-
ing technique with no sharpening. What that means is you may even get a better result if
you resize the image correctly to a lower resolution on your own and sharpen the result.
See the chapters in Part Vand the Appendix for more information about printing and
resolution.
If you think you might ever use the shot for more than one purpose, grab all the resolution
that you can with your digital camera.
12 ■ chapter 1: Resolution: The Cornerstone of Image Detail
4456c01.qxd 3/1/06 3:04 PM Page 12