FW: Scanner Resolution

[Kondla, Norbert SRM:EX]

-----Original Message-----
From: Cris Guppy [mailto:cguppy at quesnelbc.com] 
Sent: Saturday, January 18, 2003 10:14 PM
To: Kondla, Norbert SRM:EX
Subject: Scanner Resolution



This might be of interest to leps-l subscribers.

 

Scanners can be used to "photograph" butterflies or butterfly parts
(genitalia, wings) placed flat on the scanner plate. Quality of image
decreases with increased distance from the scanner plate. The question is,
what is the maximum useful scanner resolution for "photographing"?

 

Visible light wavelength = (Violet) 0.4 - 0.7 (Red) micrometre 

1 inch = 2.5 cm = 0.025 metres

1 micrometre  = 0.000001 metres

 

A scanner resolution of 1,000 dpi (dots per inch) 

= 250,000 dots per metre  = 1 dot per 4 micrometres.

 

A scanner resolution of 10,000 dpi

= 1 dot per 0.4 micrometre 

 

A scanner resolution of 5,700 dpi

= 1 dot per 0.7 micrometre 

 

So the theoretical maximum resolution of a scanner to obtain the full range
of visible colour in the image is 5700 dpi. A US$200 Hewlett Packard scanner
these days has a maximum resolution of 2400 dpi, so they are 42% of maximum
theoretical resolution. Not too bad!

 

The scanners also have an "enhanced resolution" up to 99,999 dpi, the value
of which is unclear to me (anyone else?).

 

Cris Guppy

 

 

 


 
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