Black Calibration
1 What does this mean?
Finding the sensor output value, per pixel, in the absence of any illumination.
It covers: - dark frame subtraction - dark current compensation - using black reference columns (called "optical black" by other manufacturers) to find the black level and to correct some of the row noise
Note: black reference columns can be used to reduce row noise, that's why we include it here. That means, we will correct some (but not all) of the row noise as part of black calibration process.
2 Calibration methods
2.1 Dark frame subtraction
This is a basic technique: take a picture with the lens cap on. To make really sure no light is reaching the sensor, also cover the entire camera with something.
2.2 Dark current
2.2.1 Simple correction
2.2.2 Dark current nonuniformity correction
2.3 Black reference columns
This sensor has 8+8 columns that can be used for calibrating the black levels; they are also useful for reducing the dynamic row noise.
2.3.1 Black level
2.3.2 Row noise correction from black columns
3 Proposed calibration pipeline
Step 1: use black reference columns to find the black levels for odd and even rows Step 2: subtract dark offset and dark current Step 3: use variations in black reference columns to reduce row noise