Dmin, Dmax and actual Dynamic Range

[Mike]

Has anyone put the scanners below to the test of how well they can
detect the actual dynamic range of an image and values for Dmin and
Dmax? The manufacturuers seem to focus more on the number of discrete
readings they can provide rather than the range of information from
the image.

I am looking at two scanners (already have the dual scan III), the
scan slite 5400 and the Nikon V ED.

The scan elite 5400 (as well as the dual scan III) boast a dynamic
range of 4.8. That seems to be more based on the number of bits (16
per channel) than anything else. The Nikon ED V appears to provide 12
bits per channel.

While I do care about the number of bits per channel, I also care
about how well the scanner can pick up detail based on the actual
dynamic range of the image.

The link below provides some information for what I mean by dynamic
range of the image versus the number of bits used to represent that
range.

http://www.scantips.com/basics14.html

 

[Jim]

Has anyone put the scanners below to the test of how well they can
detect the actual dynamic range of an image and values for Dmin and
Dmax? The manufacturuers seem to focus more on the number of discrete
readings they can provide rather than the range of information from
the image.

I am looking at two scanners (already have the dual scan III), the
scan slite 5400 and the Nikon V ED.

The scan elite 5400 (as well as the dual scan III) boast a dynamic
range of 4.8. That seems to be more based on the number of bits (16
per channel) than anything else. The Nikon ED V appears to provide 12
bits per channel. Make that 14.

While I do care about the number of bits per channel, I also care
about how well the scanner can pick up detail based on the actual
dynamic range of the image.

The link below provides some information for what I mean by dynamic
range of the image versus the number of bits used to represent that
range.

http://www.scantips.com/basics14.html

I don't have a problem with this reference.

The real problem is that there is no agreed definition of what manufacturere
mean by dynamic range. It is certainly true that the more bits, the more
the dynamic range can be.

However, you will note that no film has a dynamic range that approaches the
potential of either scanner. So, I would expect that you would not be able
to see any difference between scans of the same original.

By the way, density is the logarithm to the base 10 of the inverse of the
transmittance. Thus, the minimum D can never be less than 0. However,
there is no limit to the maximum D.

Jim

 

[Don]

As Jim stated, there is good reason for having a scanner with way more
"dynamic range" than the film. It affects one component of the
scanner-induced noise at high densities. For a simple example, consider a
16-bit B&W scan. A reading of 0x01 corresponds to a density of 4.8, 0x2 to
a density of 4.5, 0x3 to a density of 4.3, etc. Those are *big* density
steps, and will introduce a lot of RMS noise and posterization to the
portions of the image at those densities. It isn't until you get to a
reading of about 0x2a (a density of 3.2) that the density step size is
reduced to .01, which is a fairly reasonable amount corresponding to an RMS
density noise of about .003.

Coincidently, a density of 3.2 is fairly representative of the maximum
useable density of good film (at least B&W film).

The effects with color film are somewhat more comples, but the principle is
the same.

Don

 

[Mike]

So, slide film has a Dmin, Dmax and dynamic range in terms of the
dynamic range.

I understand the more bit depth the better becuase it reduces noise
and provides finer steps in the captured range.

Is the answer that the scanners capture the complete range of a slide
and now its just about the number of steps that represents that range?

Has anyone tested the scanners (is there a URL of results) for how
well they capture the range in a slide? If the range is not captured,
having lots of steps still leaves part of the image poorly
represented?

 

[Andy Salnikov]

So, slide film has a Dmin, Dmax and dynamic range in terms of the
dynamic range.

I understand the more bit depth the better becuase it reduces noise
and provides finer steps in the captured range.

Generally not true, more bits does not mean lower noise, only that
you can sometimes do more precise noise digitization

Andy.