Re: scanner density-value relation

From: Michael Koch-Schulte ^lt;[email protected]>
Date: 03/08/05-11:09:13 PM Z
Message-id: <00a201c52466$231d15e0$b200a8c0@Sweetwood>

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.
Received on Tue Mar 8 23:10:08 2005

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