Re: scanner density-value relation

From: Richard Knoppow ^lt;>
Date: 03/08/05-11:54:21 PM Z
Message-id: <005b01c5246c$74194c10$9bf85142@VALUED20606295>

----- Original Message -----
From: "Michael Koch-Schulte" <>
To: <>
Sent: Tuesday, March 08, 2005 9:09 PM
Subject: Re: scanner density-value relation

> Ryuji Suzuki wrote:
>> If you use step tablet of a large enough patch size, you
>> can average a
>> large region within the patch to reduce the measurement
>> error. This is
>> how I figured out my scanner's linearity limit. I know
>> the noise is
>> one important issue but my question is related to
>> linearity not the
>> noise.
> There's also light fall off at the edges to consider the
> effect is present
> even with a diffusion source. My Epson 3200 is advertised
> as 3.4 but it
> barely makes it to 3 if you are using a step wedge to
> judge. I did
> rudimentary tests using step wedges to find this out. I
> also noticed that if
> I rotated the step wedge 90 degrees or only scanned a
> small portion (the
> light lid only turned on for a brief amount of time) my
> results would
> drastically change for the better or worse. For the most
> part the graph was
> fairly linear except for the extremes (beginning and end
> portions). I found
> that by using Vuescan as my scanner driver and increasing
> the exposure from
> the nominal value of 1 to 1.2 help to straighten out the
> line a bit too.
 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

Richard Knoppow
Los Angeles, CA, USA
Received on Tue Mar 8 23:54:39 2005

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