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Re: filmscanners: LED Illumination for Film Scanners

Just two days ago, I was at a local retailer who showed me the new HP 
scanner/copier (which is basically an inkjet printer and a scanner on 
top).  It was only $399 CAN, and they have reduced the footprint to that 
of a small inkjet printer.  Pretty amazing.

The part that relates to this discussion, is that they were just setting 
it up, and that included a calibration process for the color and black 
ink heads.  It is now an automatic function.  The printer printed a set 
of varying matrixes and lines in both black and yellow.  The print head 
also had a very bright blue LED which went on, and I expect some type of 
sensor, which read the resultant printout.  When the blue LED was on, 
the yellow printing probably became gray, and the system probably tried 
to find the placement of the yellow and black lines which made for the 
highest contrast (which would be when the yellow and black lines printed 
on top of each other exactly).  I assume the unit than used this 
information to either physically adjust the head positioning, or to 
change the printing pattern to use certain nozzles and delays between 
the black and color cart, so that the ink would be printed onto the 
paper in registration.

It was a pretty neat idea, all made affordable by a blue LED.


Clark Guy wrote:

> On a historical note, back in the late '80s and early '90s, blue LEDs were
> very dim.  They were made from Silicon Carbide, and put out less than
> 100mCandela while good red or green LEDs put out in excess of 1000mC.  I
> used a particular HP red diode that put out 3-4 Candela! from a T-1 package
> (small size).  In the mid '90s I saw an example of a (then) US$50 blue
> ultribright diode.  It put out at least one full Candela of power, but it
> was too expensive for my medical diagnostic device application.   This
> weekend, I went to the drugstore to buy some film , and found a
> blueish-white LED flashlight for sale for ~$8.00  It is blinding in it's
> intensity!!!  Clearly the state of the art is moving forward at quite a
> rapid pace!
> Hope this helps!!
> Guy Clark
> --


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