[filmscanners] RE: Newish Digital Tech

["Tyler Harris" <TylerH@tetratec.com>]

Sorry, lost track of who wrote this:
<<<Although the Foveon chip measures "all the red", each individual site
measuring red measures _the same amount of red_ as any individual site
measuring red in a Bayer sensor.>>>

Austin Franklin wrote:
<<<There must be some decrease in transmission...  All the Bayer sensors
measure %100 of the light that particular sensor is filtered for, where
the Foveon gets decreased light to the inner two sensing areas.>>>

This last sentence in particular bothered me.  I did a quick search to
find the efficiency of Bayer filters and stumbled upon the following
page <http://www.mic-d.com/curriculum/imageprocessing/cmoschips.html>.
About half way down the page there is a nice colorful graph of "Typical
transmission spectral profiles of the common dyes utilized in the
construction of Bayer filters."  According to this particular graph, red
is the most efficient @~38%, then green @~30%, and finally blue @~23%.
Note also, there is considerable wavelength overlap between the three
filters.

Perhaps the Foveon could be more efficient than a Bayer filtered CCD?  I
know little about how light penetrates into silicon or whatever it is,
but since red light (long wave / low energy) penetrates further than
blue (short/high) (opposite of the ocean analogy someone gave) it seems
that the wavelength, not energy, is the critical factor.  Which, to me,
raises the possibility that little or no red light, for example, may be
absorbed by the blue sensing layer.

Anyone know how this really works?

Tyler Harris

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