Digital BW, The Print

Quantum efficiently  has nothing to do with it.  Red is at the low end 
or the visible frequency spectrum. Normally the higher the frequency the 
wider the bandwidth of filters at that frequency, unless you use a local 
frequency reference to down convert the signal. Why is this not the case 
for red light which is a lower frequency than blue light? Different 
materials for CCD's have different frequency reposes. I guess I don't 
understand why "red" produces more energy output.

The energy of a photon is Planks constant X it frequency. A photon of 
blue has more energy than a photon of red. Different scanners use 
different light sources. I am still at a loss - not that I am disputing 
it - with your statement. I just don't understand.

Truman

Austin Franklin wrote:

>Hi Truman,
>
>  
>
>>Why do you say red has " the highest energy of the three." I would
>>expect that would depend on the spectrum of the light source and the
>>bandwidth of the filters. Please elaborate.
>>    
>>
>
>The light source is a white light, and has all colors, it is filtered with
>"a" color filter, and only light of the color of that filter reaches that
>sensor.  Red just simply has the highest energy of the three, as far as the
>CCD "sees" it.  It has to do with the quantum efficiency of the CCD (how the
>CCD reacts to different spectrums of light).  Red typically has up to an %80
>quantum efficiency.  Blue and green only top out at about 60% right at their
>peak sensitivity.  Red stays quite high for almost the full width of its
>sensitivity.  Also, the spectral width of red is very very high, from 575nm
>to 850+ nm.  Blue is 375nm - 550nm and green 450nm - 625nm.
>
>Bring a color image into PS and thumb through the channels (CTL 1, 2 or 3
>for RGB, and CTL ~ for all), and you'll see that red is easily the fuzziest,
>blue and green are very image dependant as to which is better...
>
>Regards,
>
>Austin
>
>
>
>
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