V1.02
Thom Hogan’s Complete Guide to the Nikon D300
Page 35
Unfortunately, it’s not quite so simple to just state a resolution
“number” like I just did in the last paragraph. Digital cameras
do well up to a point, and then they “break down” in terms of
resolving objects. If you photograph a black and white test
chart (see example, below), you’ll find that the digital camera
simply does far better than the film camera up to the point
where digital sampling artifacts get in the way. In other words,
there’s a difference between what happens when detail goes
beyond the resolving power of an analog device (film) and a
digital one (a DSLR such as the D300).
On such test charts, the digital camera generally has higher
contrast and clarity up to the point where the pattern becomes
close to or slightly less than the sampling frequency. Note
how the big, diagonal lines above the “10” in the above
example are resolved well but as we get to smaller and
smaller versions (to the left) the lines start getting “beat
frequencies,” or false line reflections (very obvious in the
diagonals above the “5” and “6”). (See also the example
shown in “Sharpening,” on page <407>).
The anti-aliasing and Bayer filters digital cameras need (see
“The D300 Sensor” on page <48>), unfortunately, complicate
calculating exactly where the real resolution versus false
resolution changeover occurs. As you can see, once the
samples are too small, it might look like detail is being
recorded, but this is false detail—mostly artifacts
8
that mimic
8
Artifact
, used in this context, means an unwanted visual side effect. Digital imaging
is full of artifact-producing technologies—the analog-to-digital conversion,
sharpening, noise, and JPEG compression, for example—but for the most part these
artifacts are extremely small and subtle and don’t impact image quality in ways that
most people can see. Certainly you can’t see these artifacts by casual, arm’s length
observation.
