Resolution of scanned images is
measured in Dots Per Inch (DPI). This number informs the user how many pixels,
or squares, there are per inch. Higher DPIs translate into better resolution
(the ability to see detail on the scanned image) but they also mean larger file
sizes. Since DPI describes area, file size grows exponentially with increases in
resolution.
For a 9x9" black and white aerial photograph at
a map scale of 1:12,000, the following table gives an idea of the trade-off
between file size and resolution.
Therefore, a 1:12,000 image scanned at 400 DPI
will be 11.8 Megabytes but you should be able to discern items on the photograph
which are greater than 30 inches in the real world. For example, if you
were interested in looking at shrubs in a photograph, you would want to scan at
a resolution greater than 100 DPI because most shrubs are smaller than 120
inches across.
There is also a
trade-off
between different image formats and the software that can use them.
