8. Capturing Images 85
B
′
= B (8.6)
Note
When switching between these two binning modes, Luma property doesn’t
change. Luma value is calculated in pre-processing module, while subsampling
is performed later in the image processing chain (see Chapter 7).
8.2 CALIBRATION
NECTA camera is able to automatically correct non-uniformities introduced by image sensor, lens and
lighting system; the set of techniques used to improve the quality of the acquired images is generally
called Shading Correction or Flat-Field Correction (FFC), and is a combination of offset and gain com-
pensations. The calibration procedure combines three corrections involved in different phases of the
frame acquisition process:
• Black level offset,
• Dark Signal Non-Uniformity (DSNU),
• Photo Response Non-Uniformity (PRNU).
All reference images must be captured using Video Mode 1 (RAW) and at the same operating tempera-
ture required by the application; the acquisition chain parameters (e.g. Shutter, Analog Gain, CDS Gain)
must be set to the operating levels expected by the application.
Note
Every major change in the camera Overall System Gain (OSG) will change the
calibration conditions, as well as changes in light setup and lens, so a new cali-
bration will be needed. Gain, CDS Gain, ADC Resolution and Temperature will
change the OSG.
Note
After calibration you can alwaysuse the Shutter control to change the amount
of light coming to the sensor without affecting the camera calibration.
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