Read Noise in DN versus Bit Depth

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Last revised: 2018-08-28 22:30 GMT-5

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Introduction:
The Analog to Digital Converter (ADC) must have sufficient bit-depth to measure Read Noise.
So we expect most cameras to fall in the range of 1 to 4 Digital Numbers (DNs) for their read noise at the base ISO setting.
(At higher ISO settings read noise in DN rises so capturing read noise at the base ISO is sufficient.)

The green band indicates readings in the expected range of 1 to 4 DN.
Above this green band ADC bit-depth appears to be more than necessary. However, since not all cameras operate at their maximum bit-depth in all modes of operation, that is probably a good thing.

The yellow band is 0.7 to 1 DN; bit-depth here is borderline.
Read noise in this range can be measured but we're starting to have difficulty with Quantization Error.

The red band is below 0.7 DN; here we don't have enough bit-depth to measure read noise.

Observations:
12-bit cameras are most in need of an upgrade to 14-bits. One imagines that keeping costs down has had precedence over peak low ISO performance.
Until recently no camera has really required 16-bits to capture full dynamic range. But in these expensive larger format cameras the additional cost of going 16-bit is inconsequential.

Notes:
Data in tabular form follows (sortable by clicking on column headers).
Data source is either DxOMark (DxO) or PhotonsToPhotos (P2P).

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