Re: 16-bit A/D conversion and "calculated" dynamic range of 4.8
Re: 16-bit A/D conversion and "calculated" dynamic range of 4.8
- Subject: Re: 16-bit A/D conversion and "calculated" dynamic range of 4.8
- From: Marco Ugolini <email@hidden>
- Date: Sun, 23 Jul 2006 11:16:09 -0700
In a message dated 7/23/06 10:03 AM, Roger Breton wrote:
> I was looking at the specs of the Minolta Dimage 5400 II 35mm slide scanner
> today and stumbled on the business of dynamic range again. I know the topic
> has been discussed at nauseam here but I could not resist picking you guys
> (and gal's) brains for the relationship, if any, that you see between
> straight bit depth and dynamic range. I won't debate that a scanner
> manufacturer's stated dynamic range claim is to be taken with a grain of
> salt, at best. But what I thought was new here, in the Minolta's specs, at
> least, is the idea that there is logical relationship that can be devised
> between bit depth and dynamic range, that the two can be put into an
> equation.
Hi Roger.
There is a good explanation of the issue of dynamic range on pages 7 and 8
of this PDF file:
<http://www.gt-photography.com/articles/Imacon 949 Review.pdf>
Giorgio Trucco (a Physics major, accomplished wildlife photographer based in
the L.A. area, and member of the GretagMacbeth ProfileMaker Beta Testers
Team) explains the necessary distinction between the *capacity* of the A/D
converter and the *actual* dynamic range of a given scanner, making clear
that, while one *must* have enough bit depth in the A/D converter to
accommodate the dynamic range of the scanner, on the other hand the presence
of a given bit depth in an A/D converter does not per se guarantee a
corresponding dynamic range in the scanner. That still depends on other
factors (quality of the parts and of the craftsmanship, etc).
The example of Imacon's inflated claim of a 4.8 dynamic range for its
Flextight scanners comes to mind, which is completely based on the A/D
converter's *capacity*, not the scanner's *measured* dynamic range. In a way
it's like having a 750ml bottle, choosing to fill it with wine half-way, and
then telling you with a straight face that I'm giving you a 750ml bottle of
wine. Flim-flammery is an apt description of such a ploy, which technically
speaking doesn't tell you a lie, so much as it doesn't give you the whole
truth.
> So, if I may ask you color gurus out there, how could one work out
> such a relationship numerically? I On the one hand, I can understand,
> intutively, that as bit depth increases, from, say, 8, 12 to 16, more and
> more discrete "levels" of scene brightness can be represented in the
> computer. But how can the 4.8 dynamic range figure, which is a logarithmic
> representation, I assume, be arrived at and equated with bit depth? 16 bit
> is 65,536. Got that. But what real number corresponds to the log of 4.8?
> Assuming that this is the log of 4.8 in base 10.
It's not the log of 4.8 in base 10. That is the *result* of the calculation.
The 4.8 number is achieved through this equation:
Maximum Density = (log in base 10) of (2 to the power of 16) = 4.816479...
In other words it's the power to which 10 must be raised to obtain the
equivalent of 65536 (or 2^16).
Regards.
--------------
Marco Ugolini
Mill Valley, CA
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden