Samsung patent application US20140014818 "Pixel array, image sensor including the same, and method of compensating for local dark current" by Young Sung Cho, Dong Jae Lee, Tae Chan Kim, and Tomer Livneh propose a simple approach to compensate the black level variations across the pixel array. The idea is simple: a number of dark, light-shielded pixels is distributed in random or not-so-random way across the array, and their interpolated output is used for local black level calculations:
There are few modifications that need to be added to that application:
There are few modifications that need to be added to that application:
- Light leaks or photoelectrons diffusion to the shielded pixels can distort the black level measurements. Unless this is completely resolved in the company's ISOCELL technology, one might need to light-block the larger groups of pixels.
- dark current varies a lot on pixel-by-pixel basis. So, it needs to be somehow averaged across the neighboring dark pixels
- there are hot pixels, whose dark current is just abnormally high and carries no information about other pixels in the area. They need to be excluded from the dark current calculation process.
