CV-L108CL
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6.2.
Pixel Gain (flat-field) correction (PRNU correction)
Pixel Response Non-Uniformity is, as the name expresses, a non-uniformity of the response of each
individual pixel. This means that for a fixed light level each pixel will have a slightly different
output level (response).
To correct for PRNU, the camera‟s internal correction circuit captures one or several lines of data
under non-saturated illuminated conditions (not more than 80% of maximum - recommend level is
half of maximum), and the average across the line is calculated. Based on this average, coefficients
are then generated for each individual pixel. The coefficient has the function of multiplying the
pixel output with factor greater or less than 1. These coefficients are stored in a non-volatile
memory, and are therefore maintained after power down.
6.3.
Pixel black level correction (DSNU / FPN correction)
Dark Signal Non-Uniformity or Fixed Pattern Noise is, as the name expresses, fixed pattern on the
sensor output, which is
not
dependent on the incoming light.
To correct for DSNU/FPN, the camera-internal correction circuit captures one or several lines of
data under dark conditions (the lens
must
be covered by a lens cap), and the average across the line
is calculated. Based on the average, coefficients are then generated for each individual pixel. The
coefficient has the function of adding or subtracting a value to the pixel output. These coefficients
are stored in a non-volatile memory, and are therefore maintained after power down.
As the dark signal is highly dependent on the exposure time, this correction must be performed
under the operating conditions (exposure time and line rate) that will be used by the application.
Max
Min
Multiply by
Factor > 1
Multiply by
Factor < 1
Before correction: Non-uniform response from pixel to pixel
Average
After correction: flat response from pixel to pixel
Average
Max
Before correction: dark signal non-uniformity from pixel to pixel
Subtract factor
Add factor
Min
Average
