Re: scanner density-value relation

From: Richard Knoppow ^lt;>
Date: 03/09/05-02:45:52 AM Z
Message-id: <002101c52484$6e5bcc40$c8fe5142@VALUED20606295>

----- Original Message -----
From: "Ryuji Suzuki" <>
To: <>
Sent: Tuesday, March 08, 2005 11:56 PM
Subject: Re: scanner density-value relation

> From: Richard Knoppow <>
> Subject: Re: scanner density-value relation
> Date: Tue, 08 Mar 2005 21:54:21 -0800
>> I wonder if flare is a factor. The test is to mask off
>> the
>> area of the step wedge so that the rest of the field is
>> not
>> illuminated.
> In his case, maybe, because he reported such a drastic
> sensitivity to
> location/direction. Mine is very different, as I tested
> with a step
> tablet and also with large pieces of ND filters. I also
> compared with
> the reading of a small piece of opaque stuff, forgot what,
> but
> probably a metal foil sandwich-glued with black paper, in
> which some
> papers and films are packaged. So I don't think it was
> flare or
> internal reflection. If my scanner were that bad, I'd call
> customer
> support for refund before I write here :-)
> I remember writing some MATLAB codes to load the raw TIFF
> and do
> statistical analysis, curve fitting, etc. but lost it
> somewhere when I
> switched my computer. Now I'm interested in making a color
> densitometer again to quantitatively record the effect of
> emulsion
> formula, developer formula and toning to the image hue.
> Typically blue
> and red reflection densities are used for those studies
> but I don't
> have a color densitometer. With advertised Dmax of 4.0
> (say that's
> bogus and the linear portion goes only to 2 point
> something -- Warning
> -- it's a number I just made up) it's still useful for
> routine
> densitometry of pictorial negatives and prints.
> By the way, if the quality of software is entirely
> disregarded, are
> Perfection 4990 and Canoscan 9950F very closely comparable
> in terms of
> image quality as far as b&w negs and prints are concerned?
> What about
> usable Dmax?
> (Those online reviews using dark background with fine
> patterns as the
> test target are not very useful for this purpose because
> they can't
> separate the noise issue and the linearity issue.)
> --
> Ryuji Suzuki

  A simple densitometer can be very useful, even for some
color work. I have an ancient Weston densitometer which uses
a large selenium cell similar to, but larger than, those
used in Weston exposure meters. It has a shaped pole meter
so it gives reasonable readings up to a density of 3.0 on a
single scale. This is higher than usually encountered in B&W
pictorial negatives. It allows me to get some idea of the
contrast of negatives, their fog level, and general curve
shapes. I would love to have a "real" densitometer but that
will have to come in the future. It seems to me that a
decent scanner ought to be quite servicable for making
sensitometric measurements. For that matter reasonable
measurements of density can be made visually by comparison
to known neutral density filters.

Richard Knoppow
Los Angeles, CA, USA 
Received on Wed Mar 9 02:46:19 2005

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