Digital BW, The Print

Anthony,

> > Anthony - can you explain "depth of
> > modulation" to me?
>
> I'll using printing for an analogy, since that seems appropriate here.
>
> When you print something (for example), each pixel printed is constructed
> from an appropriate number of pixels in the input file.  It is rare that a
> one-to-one correspondence exists between input pixels and printed
> pixels, so
> usually some interpolation takes place.  This interpolation reduces the
> accuracy of the printed pixels as compared to the input pixels;
> that is, the
> printed pixels won't represent the image quite as accurately as
> the original
> pixels did.

I believe you are misusing the term pixel here.  Printers, at least the
inkjet ones we use here, print dots, they do not print pixels.  There is a
huge difference between a pixel and a dot.

Also, the printer drivers for these inkjet printers do not "interpolate",
that is something entirely different.  They "dither" (amongst other terms).

> Now, if the number of pixels coming in is the same as the number
> coming out,
> the loss depends on how well they are aligned.  If the number of pixels
> coming in is less than the number going out, the true capacity of the
> printing device won't be used.

That's not correct for inkjet printers that dither/halftone.  What matters
is how large an area is used to represent the tones, and that area can be
variable.  Do you really understand the dither/halftone process?

> So the key to printing nice results would seem to be to send in
> more pixels
> than you intend to print; and this is actually how it works.  However, the
> principle of diminishing returns rapidly applies.  Up to about
> 1.5x, adding
> pixels on the input side improves the output noticeably, even
> with its fewer
> pixels; but beyond 1.5x, the bang for the buck diminshes, with additional
> pixels making less and less difference, until it simply makes no
> discernable
> difference at all to keep increasing input pixels.

I don't know what printer you are trying to talk about here, but that's not
the case for inkjet printers that we use here.  They print at 1440 (or
whatever) DPI, and input up to 1/2 that is usable with the Piezo driver, and
probably 1/4th that or so with the Epson driver.

> Kodak says
> that 1.5x is
> a good ratio, and I tend to agree.

Kodak says that about WHAT printer?

> Of course, all of this applies to digital cameras, too.  Having
> extra pixels
> in the CCD beyond those that you output means that your output pixels will
> be better chosen, and the image will be cleaner.

No digital cameras that I am aware of have "extra pixels in the CCD..."
(digital cameras have sensor elements BTW, not pixels...unfortunately,
another commonly misused term).  What cameras do you know do this?

Austin