12 vs 14 bits? difference? 1000D

Started Jun 10, 2008 | Discussions thread
Boky Regular Member • Posts: 426

It is all gray scale capture, with the gray scale value directly proportional to the amount of red, green and blue (or CMY... depending on the type of filter used in front of the sensor) light. The sensor counts photons - it is very "stupid" device – and it outputs analog signal proportional to the amount of photons captured. The raw format contains gray scale value for each pixel, and it also contains “decoding” information to tell the processor which pixel was behind what colour filter.

Dynamic range is basically divided in to 6 “levels” or stops. The brightest one gets the biggest “chunk” of 12 bit A to D converter quantisation: 2048 levels (with 14bits available, the brightest “stop” will get 4X the amount of 12bit converter = 8192 levels of tonal information). This is why it is very important to “expose to the right” – so that you can utilise full dynamic range available while keeping the “signal” well above the noise floor, especially with 12bit cameras.

The most important thing is that the darkest “stop” will get only 64 levels of tonal information with 12bit A to D converter, where with 14bits this number is around 256!

Highlight tone priority works by preserving highlight information while counting on more dark shades levels that 14bit conversion is providing – by underexposing, basically.

14 bit conversion is the overture to high dynamic range sensors, which could capture more than 6 stops of brightness.

I think 14bit A to D conversion is a good thing that will allow easy high DR sensor implementation.

In the meantime while waiting, the every-day difference between 12 and 14bit photos may be visible in the amount of details captured in dark areas, better - smoother colours, more flexibility in PP, better chance to recover underexposed photos...


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