Digital BW, The Print

Anthony,

> The main reason this isn't always obvious in practice is that very few
> images make use of all sixteen bits.

In fact, none *really* do.

> For example, digicam images or
> scans may only have 12 or 14 bits at most.  As a result, they tend to
> posterize almost as badly in 16-bit manipulation as they do in 8-bit
> manipulation.

That's not true.

> However, if you really do have a full 16-bit image (one that contains
> data in all 16-bits, like an extremely high-quality scan or digital
> capture),

No scanner or digital capture device used in any current commercial product
will give you 16 bits of real data.  There are a number of reasons for this.
One is simply the sensitivity of the imaging sensor/system (noise), and in
the case of the scanner, is that typically a scanner is designed so that the
image only occupies a portion of the 16 bit space, and you set your
setpoints to then expand the image into the extents of the 16 bit space.
Typically, in a digital camera, the setpoints are already done for you, so
this "expansion" happens automatically.  Another reason is the bits are
insignificant to out our human vision system, and we can't really
print/display them anyway...

Regards,

Austin