[filmscanners] RE: rebuild your scanner and get better results

["Austin Franklin" <austin@darkroom.com>]

Hi Andras,

> > > LED intensity is hard to control without feedback because their
> > > response of intensity to voltage and current isn't linear.
> >
> > That really doesn't matter, as it is then calibrated...so there
> IS feedback,
> > per se.
>
> OK, but calibration is only done for one intensity -- the scanner only
> stores one value per pixel as calibration data (not even one for each
> colour channel).

That is a bad design in my book.  You can get banding by doing that, as well
as inaccurate color.  They SHOULD have calibration for all three colors,
whether it's the light source that changes for each color, or they use a
tri-linear sensor...or in the case of the 8000, they do both I believe.

> > BTW, it appears you didn't mean it's technically difficult to
> make the LED
> > variable, as it really isn't, but that it's more difficult to do it with
> > "accuracy"...
>
> OK, that's what I meant. To maintain colour balance, however, you have
> to control the LEDs pretty accurately.

I'm not a fan of LED light source, and I believe the 8000 uses a monochrome
tri-linear sensor, and changes the color of the light source and takes three
exposures per line...and as I said above, not calibrating, and providing
calibration correction for, each line of the tri-linear sensor by it self
can lead to banding...and apparently that's what was discovered as the cause
of banding on the 8000.

> > One of the issues with having multiple light sources, as these LED light
> > sourced scanners do, is that the light sources do overlap (they have
> > to)...and this can cause banding problems more so than a single
>
> No, they don't overlap. LEDs emit a very narrow band of light (in
> terms of frequency/wavelength), and the bandwidth is much smaller than
> the separation of the LEDs (few nm as compared to few 100 nm).
>
> How would this cause banding, BTW?

I don't quite know what you are saying above...as LEDs have a rather wide
angle of dispersion, and that really has nothing to do with the
frequency/wavelength.  I'm talking about physical coverage, not
frequency/wavelength.  Again, I don't believe there is a physical light gap
between adjacent LEDs.  If they did, as I said, then there would be gaps in
the illumination...even with a diffuser, the middle area would have slightly
degraded illumination...and as I said, that could cause very noticeable
banding.

> ...there is no
> setting for LED intensity. The LS-8000 is no exception.

We should possibly ask Ed Hamrick about that, but needless to say, I'm
skeptical as far as the 8000 goes.  Though you may have "a" scanner
interface document, it may not contain everything.  Like Epson does, there
may be different levels of documentation, and these are only available to
approved developers.  I'm not sure Nikon does this, but it is somewhat
standard in the industry to do so.

Regards,

Austin


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