40
NED
XCM20160T2CXP
UME-0054-01
5.12 Pixel Correction
As a rule, image sensors (CCD, CMOS and so on) have fixed pattern noise and
photo response non-uniformity. Lens shading and light sources can also cause
non-uniformity. The camera is set to the optimal correction before shipping in order
to provide images of the highest grade.
The camera also has a user white correction function to cope with lens shading and
non-uniform illumination, or to be able to completely clear the uneven brightness
generated by changing the spectral response level of the light source. Cal_bl:
Output data of each pixel at perfectly dark (digital)
Cal_wh: Output data of each
pixel in uniform illumination (digital)
Target_Val : Target value for correction (10bit
digital)
Vin : Input data (digital) Vout : Output data (digital) The corrected data is
expressed in the following equation.
Vout=(Vin-Cal_bl) x Target_val / (Cal_wh-Cal_bl)
Waveform before bit correction
Output
Pixel Number
Waveform after bit correction
Output
Pixel Number
Figure5-12-1 Waveform before and after bit correction
