Page 28
Setup Manual
C.1
White Balance
The white balance function is the most important function for consistent image quality.
To ensure optimal performance, the WideTEK 25-600 should be calibrated in regular
intervals to compensate for light degradation, variations in the paper quality of the
documents to be scanned, and other long term effects.
C.1.1
Helpful information about White Balance Adjustment
The scanner has built-in light sources of known and stable quality consisting of state-of-
the-art white LEDs.
In the first step, the overall sensitivity of the scanner is adjusted in such a way that the
brightest area results in an almost saturated output signal. This assures that the largest
density range possible is used. After this adjustment is done, the uneven light distribution
on the CCD caused by the imbalance of the lamps, the ambient light introduced, the
imperfections of the lens and other factors has to be compensated for.
This measurement results in a correction function which levels the brightness over the
complete scan width.
The quality of the test target is of utmost importance to the result of the white balance.
The test target is on reflective paper which diffuses the light. If the test target has dirt,
wrinkles or anything visible to the human eye on it, the CCD will also see this and will
overcompensate in these areas. Although the internal software has been programmed to
eliminate these imperfections to a certain degree, it still leads to unreliable results if the
target is not of the defined quality.
If the target is of defined quality, the scanner will calibrate successfully. Calibration means
that the “white” of the test target in the given illumination situation produces a “white”
output in the digital domain. Consequently, all scans of white paper having different
properties than the test target results in brightness and possibly color shifts.
Periodically performing the white balance adjustment is recommended to ensure
consistent best scan results.
