Re: Sensor filters
Re: Sensor filters
- Subject: Re: Sensor filters
- From: email@hidden
- Date: Sat, 27 Jul 2002 11:38:32 EDT
In a message dated 7/26/02 5:43:40 PM, email@hidden writes:
>
There is much misinformation about scanners and digital cameras. The
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selection of the peak responses for the filters was not made to optimize
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their response to CMY inks. The reason is much simpler.
>
>
The sensor filters traditionally were selected by dividing the visible
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spectrum of 400 to 700 nm into three regions corresponding to 400-500,
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500-600 and 600-700 nm. The filters were then designed to have peak
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sensitivities at the center of each of these regions; 450, 550 and 650
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nm.
Or one could claim they were designed to emulate the cone responses of the
human eye... at least roughly.
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By doing this, the conversion matrices for RGB to XYZ are often
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simplified to 3x3 matrices, making conversion fast and simple. It also
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simplifies some operations for color constancy calculations.
I'd rather have more complex math, and closer emulation of the eye's
response...
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Scanner filters were not designed to be optimized to CMY film dyes or
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printing inks.
Wouldn't really be practical anyhow, since these materials have such a broad
spectral range. Instead of the type of tight wavelength zone that LEDs light
sources are capable of,
reflective inks are hugely broad, with each ink color covering a large
section of the spectrum, and inevitably stimulating more than one of the
eye's cone types, and more than one of the filtered sensors of a camera or
scanner. The crossover between the green and blue sensors in scanners is
particularly problematic when attempting to use them for exacting
colorimetric purposes.
C. David Tobie
Design Cooperative
email@hidden
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