Re: Let's have a discussion about SCANNER d-max

[hult@xxxxxxxxxxxxxxx (Marc F. Hult)]

On Mon, 14 Dec 1998 07:14:27 -0500,
Benjamin_Gottlieb@xxxxxxxxxxxxxxxx (Benjamin Gottlieb): wrote:

>     Maybe I should start by asking what is a d-max
>
On Mon, 14 Dec 1998 08:16:21 -0500 (EST),   YDegroot@xxxxxxx: replied

>D-max is the density a film/slide/reflective scanner can read, that 
> is: the higher the d-max, the more shadow details it can read.

Usually not.

Beginning in the 1880's,  Maximum Density (D-max) was defined as the
densest part of the characteristic (Hurter and Driffield) curve of a
black and white negative film. With reference to a film with a
pronounced shoulder (where response rolls off with increased exposure,
D-max is the highest density that a given film/developper combination
can attain under any circumstances. This is usually determined during
the course of sensitometric testing.  Newer negative films can obtain
a D-max that is significantly greater than what is useful in typical
photographs. 

D-max can also be used to refer to the maximum density in a
_particular_ negative, slide or print rather than the properties of a
film-developer combination.  It from this later usage of the term that
D-max with respect to scanners seems to have evolved.

The ability of a scanner differentiate between slight differences in
photographic densities near D-max is important with respect to
_highlight_ detail of the final image when the material being scanned
is a negative, and with respect to shadow details when the material
scanned is a positive. 

A "scanner D-max" adequate for a particular image is necessary but not
sufficient to assure highlight/shadow detail. If there is inadequate
resolution, increasing D-max will have negligible effect on the
_detail_ in the shadows (or highlights as the case may be) in the
resulting scan.   As a practical matter, most of the terms
(e.g."D-max") and specifications provided my scanner manufacturers for
their consumer-grade products are misleading at best.

This has next to nothing to do with Panorama and I apologize if the
post is off-topic but the topic seemed destined to be discussed .

HTH ... Marc
-- 
Marc F. Hult
hult@xxxxxxxxxxxxx