Bio-Rad Image Lab™ Software - Manual (Page 128)

8 | Analyzing Images
128 | Gel Doc XR+ and ChemiDoc XRS+ Systems with Image Lab Software
Advanced Detection Options
 Sensitivity — determines the minimum optical density that will be defined
as a band. The higher the sensitivity value, the lower the minimum signal
intensity, therefore the more bands will be detected.
If the sensitivity is set too high, background staining might be detected as
bands. If the setting is too low, bands of interest might not be detected.
The default sensitivity setting is 10.0. If the gel has faint bands (for example, if
the optical density is less than 0.05, and counts are less than 2,000), you may
want to increase this value to 20.0.
 Size Scale — distinguishes between trends in signal intensity and random
intensity fluctuations. It is the number of pixels in a vertical column that are
taken together to determine whether a band is present.
The Size Scale parameter uses the size of objects in the image to determine the
nature of those objects. If a gel image has high levels of background noise, a
larger size scale is appropriate. At low noise levels, a smaller value is preferable.
You can also increase the size scale if the gel has only a small number of thick
bands scanned at high resolution.
 Noise Filter — minimizes the number of small fluctuations (or noise) in the
image that are called bands while still recognizing larger features (the real
bands). This filter becomes especially important at higher sensitivity levels.
The noise filter value refers to the size of the filter in pixels (for example, a value
of 2.50 equals a filter size of 2.50 x 2.50 pixels). Features smaller than the filter
size will not be recognized as bands. Entering a noise filter size of zero turns it
off completely.
If band detection identifies doublets as single bands, decrease the noise filter
setting and/or increase the sensitivity level.
Tip: You can also decrease the Size Scale parameter instead of the noise
filter to improve the detection of closely spaced bands. However, if you
decrease both the noise filter and the size scale, the fuzziness around
bands might be mistakenly detected as separate bands.