Digital BW, The Print

Steve Kale wrote:


> do you feel that for a given Canon
> sensor (say the 1Ds MK II sensor) there is anything to be gained from
> increasing the bit depth of the ADC?

Steve, in the specific case of the 1Ds Mark II, I do not think 
additional bits (with higher sampling resolution) would be a gain. One 
additional bit halves the gain and that seems like it would be too much 
to me.

Since I'm not the sensor designer and I don't know certain important 
specs for that sensor, this is a swag. I'm basing this opinion on the 
pretty high offset for this camera and my presumption that the gain is 
similar to that on the 10D, 20D, and XT sensors. But those are not the 
only specifications that matter, and my figures for those specs are of 
dubious accuracy or applicability anyway. Perhaps someone else can throw 
in their thoughts on this.


> I was always puzzled, though,
> particularly having read the digital tonality material on Normen's site, why
> a camera manufacturer would not deliver 16 bits to the user and hence, as I
> understand it, improve the usefulness (read "editability") of those dark
> areas just above the noise threshold.

If you want editability improvement, one useful thing to do might be to 
lobby your software vendors for floating point math in image 
manipulation algorithms, and support for file storage in 32 bit float 
FITS format or some layerable equivalent.

I'm guessing (I'm not a manipulation algorithm expert) that this will 
make it harder to put gaps in the histogram, which is a popular way (for 
me at least) to ruin images under the current scheme. I'd also guess 
that much of the additional precision you get with 32 bits is empty, and 
that since editing destroys information you're going to hit an 
editability limit somewhere anyway. I'd be interested in hearing someone 
with expertise opine on this.


> But the question remains as to whether
> 12 is enough/optimal for current 35mm sensors and whether a significant
> improvement in usefulness can be achieved by increasing bit depth to, say,
> 16.

In my opinion, we're not to the point yet that 16 bits are useful for 
miniature format DSLRs from Nikon or Canon. I think it is also 
questionable whether we are there for some of the medium format backs 
I've seen or used, although certainly many of them justify the 
expression of more than 12 bits.

That we *could* get to a useful 16 bit output in DSLRs pretty quickly is 
shown by certain camera companies, like SBIG that someone mentioned, 
which use low-end (mostly Sony?) sensors with well depths about what we 
see with DSLR sensors, and which do usefully output 16 bits. So I'm not 
saying we will never be there; we're just not there yet. The latter 
sensors are cooled, and read out very slowly compared to our DSLRs, and 
they are CCDs and hence a bit power hungry. So there are engineering and 
usability incentives not to use them at this time, but improvements seem 
to be possible.

--
Jeff Medkeff
Eagle River, Alaska