Dynamic range question

Started Nov 7, 2008 | Discussions thread
GordonBGood
Veteran MemberPosts: 6,274
Like?
Re: firmware upgrade? no
In reply to RedFox88, Nov 12, 2008

RedFox88 wrote:

More dynamic range comes from higher bit sensors. Some dSLRs are now
14bit yet some are still 12bit. And next generation dSLR sensors
will be 16bit as some MF sensors are already. But with more bits
come larger file sizes which is one of the biggest cons against
higher bit files.

You are right that a camera with more bit depth could have a greater Dynamic Range (DR), but the qualification is that they must be clean noise free bits at least at base ISO sensitivity gain.

The recent 14 bit raw output cameras almost all have individual channel noise at its lowest (in the blacks where it would almost directly impact the DR) at much more the the Least Significant Bit (LSB) or 14th bit and, in fact, is greater than the LSB if these raw reading were truncated to 12 bits. In this case, the raw files may as well have been output as 12 bit depth (for greatly reduced file sizes) and had an extra two bits of random data added on the LSB end.

Cross-check (ejmartin of these forums) says in: http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html

where he says, quote: "Curiously, all the 14-bit cameras on the market (as of this writing) do not merit 14-bit recording. The noise is more than four levels in 14-bit units on all of these cameras (Nikon D3/D300, Canon 1D3/1Ds3 and 40D); the additional two bits are randomly fluctuating, since the levels are randomly fluctuating by + - four levels or more. Twelve bits are perfectly adequate to record the image data without any loss of image quality, for any of these cameras (though the D3 comes quite close to warranting a 13th bit)."

Emil does a very thorough job in his article in showing that without low noise, no matter how much the bit depth, one can not have a high DR for 100% zoom images.

All current cameras, including very high priced digital backs with 16 bit raw output, may as well have been truncated to 12 bit output and up to four bits of random data added before processing.

One of the main limitations to getting the noise lower than one 12-bit depth LSB is the converters used, so this is a main area for development for improved DR. The very least noise introduced by the converter chain was for the Pentax K10D with its 22 bit converter at somewhat less than one 12-bit LSB, but unfortunately the usable DR from that camera was limited for other reasons being pattern banding introduced through its manner of pre-processing the raw data.

Regards, GordonBGood

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