Frank Paris wrote:
The 3.9 dynamic range sounds unbelievable. I wonder how they achieve that?And Ed Hamrick wrote:
"3.9 just means 13 bits of dynamic range. They're using a 14-bit A/DThat doesn't take into account the fact that even the most recent and sophisticated CCD chips only claim a 12 bit dynamic range. Feeding a 74 dB/12bit/(call it what you will) 5000:1signal/noise ratio analog voltage into a 14 bit A/D still only gets you a useable 12 bit range.
converter, which most vendors convert to a dynamic range of 4.2.
I suspect Polaroid is just being conservative."
I suspect that the increased dynamic range is got by overscanning each
line at different exposures, and then 'stitching' the most significant
bits from the lesser exposure with the least significant bits of the higher
one.
This would naturally slow down the scan, but then maybe the 3.9D is
only available in a "higher quality/ slower speed" mode.
The relationship between bit depth and dynamic range is:
Bit depth ratio = 2^(number of bits)
Dynamic range (as density range) = log base10 (bit depth ratio)
For example:
12 bits = 2^12 (4095:1)
Log 4095 = 3.6122 D
Regards, Pete.
