Digital BW, The Print

> From: Roy Harrington
>
> Feels like we've drifted a little from the subject.  My comment
> only had to do with
> how the dynamic range of a sensor directly influenced how many
> bits you needed
> in the A/D and why -- that it is an integer arithmetic reason not
> a physics reason.

No disagreement there.

> I think you are confusing dynamic range with smoothness or
> resolution of gray
> values thoughout the scale.  Dynamic range is only a measure of
> how far apart
> the darks shadows can be from the brightest highlights.  It's a
> matter of seeing
> detail in shadows without blowing out the highlights.  Dynamic
> range is just
> a ratio -- no more.

Sure, but the dark end isn't limited by the numeric range--that goes to
zero, and you can't divide by zero. It's limited by the noise level, which
means that photographing the inside of your lens cap will give you nonzero
output. The average of that noise defines your black level.

> What I think is a common fallacy is the logic:
> 1) More dynamic range  implies  more bit depth needed
> 2) More bit depth  implies  more gray values
> Therefore:
> More dynamic range is one and the same as more gray values.
>
> This almost seems obviously true but in fact it isn't true.
> (1) is only true because you need more bits to get the max/min larger
> NOT so there are necessarily more distinguishable values in between.

I agree entirely.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...