16 bits is totally useless for digital imaging, there are some few large-cell sensors in the scientific field that can use 15bits fully. They are usually actively cooled and have cells larger than 10x10µm.
This is another part of the digital image pipeline that is sorely misunderstood... Just getting more bits of data does not in any way mean that the image contains more actual information... No Canon camera today can actually use more than 12 bits fully - the last two bits are just A/D conversion "slop" margin and noise dither.
I guess I'd dispute that. The bit depth puts an intrinsic cap on the photographic dynamic range of the digital image. DXO "Screen DR" numbers are basically the "hardware" dynamic range numbers for the cameras they test. The D800 and D600 get something around 13.5 stops, thanks to the fact that they don't have nearly as much "AD conversion slop" as Canon sensors. Canon sensors definitely have a crapload of "AD conversion slop", which increases at lower ISO settings (ISO 100, 200, and usually 400 all have much more read noise than higher ISO settings on Canon cameras), which is why they have been unable to break the 12-stop DR barrier. Assuming Canon can flatten their read noise curve like Nikon and Sony have with Exmor, additional bit depth raises the ceiling on photographic DR in the RAW files.
I would also dispute that Canon sensors can't get more than 12 bits of information. If you run Topaz DeNoise 5 on a Canon RAW file, the most heinous noise, horizontal and vertical banding, can be nearly eliminated. Before debanding, a Canon RAW usually has less than 11 stops, in some cases less than 10 stops, of DR ("Screen DR"-type DR, for correlating with DXO.) AFTER debanding with Topaz, a lot of information that would otherwise be "unrecoverable" because it was riddled with banding noise is now recoverable! I wouldn't say you have around 13.5 stops like a D800, but you definitely have a stop, maybe a stop and a half, more shadow recoverability than you did before...which might put you as high as 12.5 stops of DR.
If we had 16-bit ADC, we could, theoretically, have over 15 stops of dynamic range. With Exmor technology, I don't doubt that a camera with a 16-bit ADC could achieve 15.3-15.5 stops of "Screen DR" on a DXO test. If Canon did such a thing, assuming they don't fix their horrid "AD conversion slop"...well, at least we might get 14 stops of DR out of a Canon camera, while the last two bits of information are riddled with noise. With some quality post-process debanding, we might get 15 stopd of DR.
While most of what I do is bird and wildlife photography, and dynamic range is usually limited to 9 stops or less anyway...I do some landscape work. I'd probably do more landscapes if I had 30-50mp and 15 stops of DR, though. I could certainly see the benefits of having a high resolution 16-bit camera for landscape photography work, and it is the sole reason I would like to see full 16-bit ADC in the near future (hopefully with the big megapixel Canon camera that is forthcoming!)
This is written by John Sheehy and as the Suede, Emil Martinec BobN2 John has no emotional ties to his own camera brand Canon.
Noise isn't monolithic. It comes in various types and sources.
The most universal noise is photon shot noise, which really isn't noise, per se, but is actually the texture of the signal, as light is a finite number of randomly timed events. The more light the sensor collects, the less grainy the capture and the closer it comes to a smooth thing, like you "see" in the real world (even though that smoothness is an illusion created by the brain). This type of noise will always be cleaner at ISO 100 than ISO 160, by 1/3 stop. Every stop of increased exposure increases the signal-to-noise ratio of photon noise by a half stop. This noise is only related to the sensor exposure, and has nothing directly to do with ISO settings.
Then, there is noise that is generated at the photosite while reading it. Again, this noise is independent of ISO setting, and related only to exposure. The difference between this read noise and shot noise is that it can have blotchier character and line noise or banding, usually only becoming an issue at high ISOs where it is amplified more. Also, unlike the shot noise, the SNR of read noise increases by a full stop when the sensor exposure is increased by one stop.
Then, there is late-stage noise, which occurs after amplification of the photo-site readout. This is where the camera creates its greatest anomalies. Since it occurs after amplification, it is the same strength at all analog sensor amplifications, and exists relative to the digitized values, rather than the absolute sensor signal. It is what gives Canon DSLRs the lowest DR in the industry. Canon, rather than amplifying in 1/3 stop steps at the photosite, uses a very cheesy method to get 1/3 stop ISOs; it simply under-exposes or over-exposes the full-stop ISOs by 1/3 stop, and then multiplies the RAW data by 0.8 or 1.25 to make it look like normal RAW data. The problem with this is that the total read noise for ISOs 100, 200, and 400 are about the same, so when ISO 100 gain is used for ISO 125, the read noise of ISO 125 is actually greater than the read noise of ISO 400, and closer to the read noise of ISO 640 on most Canons! Conversely, ISO 160 is ISO 200 gain multiplied by 0.8, so the read noise is about 80% of that of ISO 100.
So basically, ISO 160 is cleaner in the deep shadows than ISO 100, by about 1/3 stop. In the highlights, however, which are dominated by photon shot noise, ISO 100 is actually 1/3 stop cleaner. Chances are, however, that you would not fully appreciate the benefits of ISO 100, compared to the benefits of ISO 160 in the shadows, as photon shot noise is very aesthetic noise, and does little to obscure image detail, as opposed to read noise which is often more like a cheese grater across your eyes.
However, if are shooting RAW and "exposing to the right", you are already creating ISOs of 160, 200, 180, whatever, out of ISO 100 gain, and are moving the read noise floor down anyway. If you are shooting JPEGs, or movies, then ISO 160 is the way to go for reduced noise, as the camera was going to discard the 1/3 stop of extra DR that ISO 100 has in the highlights that ISO 160 moves to the shadows, anyway, so there is no loss.