User guide

Quantity One User Guide
14-2
14.1 How Bands Are Identified and
Quantified
You can automatically identify all the bands in your image using the Detect
Bands command, or you can mark them individually using the Create Band
command.
Each identified band is defined by brackets above and below the band. You
can see these if you select the Brackets option button in the Band Attributes
dialog box. (Select Band > Band Attributes.) These brackets mark the
boundaries of the band.
The width of each set of brackets is set by you before the bands are detected.
This is the lane sampling width. The height of each set of brackets is
determined automatically, using a band-finding formula together with
parameters that you select.
When a band is quantitated, the average intensity value of each horizontal
row of pixels within the brackets is calculated. Next, the number of pixel rows
between the top and bottom brackets is determined. Taken together, these
result in an intensity profile for the band.
Finally, the area under the profile curve to the baseline is integrated, resulting
in units of intensity x millimeters. This is the “trace quantity” of the band.
Note: Because the profile of an ideal band conforms to the shape of a Gaussian
curve, band profiles can be “fitted” to a Gaussian model. The band
quantity can then be quantitated from the area under the Gaussian curve.
This is the best to resolve overlapping or closely spaced bands in your
images. See section 14.7, below.