Austin,
> Well, I'm not sure what you mean by "spatial profiles", but spatially, the
> light sources AND the sensors are in "spatially" different places. Also,
> changing the color of the light source means differing the exposure time,
> hence calibration for that light source. In my experimentation having
> designed a few scanners, I found that the optimum exposure times for each
> color can vary widely, and thus, calibration for each color is very
> important.
Exposure times are dealt with separately for each colour in the
LS-8000, just as it has to be. There is no need to calibrate for each
CCD element since the colour response of the CCD elements is
identical. BTW, exposure times is the same throughout the CCD, unless
you want to scan pixel-by-pixel and wait a week for a scan to
complete.
> Yes, that is one of the reasons calibration is for, but it does not
> eliminate other possible causes of banding, like I said, the LED pattern.
What do you mean by LED pattern? If you mean the fact that the
illumination by the three of four LEDs is slightly different in their
spatial distribution, then the only thing that can cause is uneven
colour balance, not banding, provided you only use one sensor line.
> The sensor operates best within a range of intensity, and adjusting the
Oh, no! It's not the intensity but the total amount of light that
should be somewhat below saturation. Saturation would mean complete
discharge of the CCD, which would cause nonlinearity. Total amount of
light is given by the product of intensity and exposure time, so why
reduce intensity and make exposure times longer?
> light level to maintain that range can help prevent, as I previously stated,
> bloom and smear. How do you feel exposure effects SNR? I'm not saying it
> doesn't, but I am curious what you believe.
The longer the exposure, the more noise you pick up. The total
discharge caused by the incident light must remain the same for
optimum use of the CCD (just below saturation). As the discharge
caused by noise increases with the square-root of time, the
signal-to-noise ratio also decreases as the square root of time. (This
doesn't take into account noise in the electronics between the CCD
cell and the A/D converter, though.)
Andras
===========================================================================
Major Andras
e-mail: andras@users.sourceforge.net
www:
===========================================================================
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