Re: Cheap scanners
Re: Cheap scanners
- Subject: Re: Cheap scanners
- From: ken rockwell <email@hidden>
- Date: Tue, 05 Dec 2000 10:14:07 -0800
The reason the dynamic range of a scanner can vary, regardless of choices of
of CCDs, PMTs and ADCs, is the action of the analog circuitry between the
image detector (CCD or PMT) and the ADC.
For instance, one can use an analog logarithmic convertor before the ADC to
do the gamma correction before digital conversion. One also can tweak the
charactoristics of the analog circuitry while pre-scanning, making things
much easier for the ADC. Analog log convertors and analog circuits that
allow adjustment of their charactoristics remotely are expensive and require
design by an expert analog designer, a rare skill today. I'm presuming that
most inexpensive scanners today use linear analog circuits and do the
fooling around in cheap DSP programmed by the droves of programmers.
It's been about 10 years since I used to help the scanner makers design
scanners when I really worked at the place that made all the ADCs used in
high-end scanners.
Hope this helps,
KenRockwell.com
San Diego, CA