Low-signal histograms at various ISOs — Sony NEX-7

At ISO 100, it looks like the NEX-7 has a 12-bit ADC:

At ISO 200, more noise:

at ISO 400 still more noise. Note that we’ve not seen the bucket at 32 counts occupied in one of the histograms so far :

At ISO 800, still more noise, and still nothing happening at count 32:

At ISO 1600, the missing codes are at 20 and 64. I don’t think that’s because of digital gain, because the regular code gaps aren’t any bigger:

At ISO 3200, the engineers have switched to digital gain. We now have 11 bits of resolution:

At ISO 6400 we get another one bit shift to the left, and the resolution falls to 10 bits: