User guide

Quantity One User Guide
17-4
17.2 Counting the Colonies
After you have positioned the circle, you are ready to detect colonies.
If you are counting plaques, click on the Plaque checkbox. (Because plaques
appear as clear circles on a darker background, this checkbox must be
selected for proper detection.)
Before counting, you may want to adjust the Sensitivity and Averaging
parameters described below.
When you are ready to count, click on the Count button.
Sensitivity
The sensitivity setting determines the minimum signal intensity in the image
that will be counted as a colony. (This is based on the slope of the signal’s
peak.) The higher the sensitivity, the more colonies will be detected.
If the sensitivity is set too high, background noise will be erroneously
detected as colonies. If the setting is too low, real colonies may be missed.
The default sensitivity setting is 10.00. If your image has faint colonies (e.g.,
O.D. < 0.05, counts < 2,000), you may want to increase this value to 20.00.
Averaging
Averaging is designed to prevent random signal noise (such as salt or pepper)
in the image from being detected as colonies. If your image is noisy, you
should select the highest value that still results in good separation of colonies
(default = 3).
A low averaging value may result in noise being detected as colonies. A high
averaging value may result in two closely spaced colonies being counted as
one.