As I have figured, the main cause for the intensity values in an image to be non-zero even in the absence of light is the dark current which propagates through the photodiodes, providing some charge accumulation which in turn creates a non-zero intensity level for pixels in the resultant image even when there is no light through the lens.
So, to alleviate this, the black level offset is subtracted from the intensity values of an image generated when exposed to light, so as to enable the proper dynamic range.
But, by virtue of manufacture, each pixel location which is basically a photodiode or a photosensitive material will have a different amount of dark current, which would imply a different correction value for each spatial pixel location.
That would mean storing a huge amount of data to identify the black level correction for each pixel. How is this issue dealt with then?