On Tue, 13 Jul 1999, Lawrence LeMay wrote:
> How important is high resolution? Is a 640x480 camera with 10X
> zoom much more useful than a 1280x960 with 3X zoom and
> no macro focusing?
One thing that has not yet been mentioned in this thread is that the
published resolutions of consumer digital cameras do not necessarily
correspond to the CCD resolution. When I was camera shopping a while ago,
the 1280x960 resolution of the Kodak DC120 seemed impressive - until I
looked at the specifications and found that it uses a single 850x984 pixel
CCD. Check the CCD resolution - it should be at least as high as the
camera's claimed resolution, and preferably higher, since portions of the
CCD are likely to be used as a dark reference or mapped out due to
defects.
Consumer digital cameras generally use a single CCD as the imaging device.
Since CCDs are monochrome, "color" CCDs are produced by applying a dye
filter to alternating pixels in the CCD array to change the hue that
different pixels are sensitive to, in a pattern such as
RGRGRG
GBGBGB
RGRGRG
GBGBGB
where R, G, and B represent pixels that are sensitive to red, green, and
blue. The true RGB resolution of a device that uses a single "color" CCD
is therefore considerably less than the resolution of the CCD itself,
since interpolation of these values is required to produce the final
image.
Such an arrangement isn't as detrimental to the overall image quality as
it may at first seem, since the human eye is less sensitive to fine image
details as variations in hue than it is to fine image details as
variations in intensity. Indeed, one of the first steps in JPEG
compression is 2:1 chrominance downsampling, so the most commonly used
compression technique would normally discard a large amount of this
information anyway.
After attempting to photograph portions of my collection using a Kodak
DC20 (a nice toy, but little more) and a Ricoh RDC-2E (somewhat better), I
have the following observations:
The noisy images that the RDC-2E produces in low-light situations compress
poorly, leading to more JPEG artifacts and even lower image quality. A
flash should help somewhat (and it would be much more convenient than the
halogen work light that I'm currently using).
The lens on the RDC-2E is too wide-angle for photographing computers at a
distance at which they fill the viewfinder, leading to a "fish-eye"
effect. A lens with variable focal lengths would be a good thing to have.
A standard file format (such as JPEG) would be great. The RDC-2E uses a
type-II PCMCIA card for storage, so transferring image files to my
Linux-based laptop is easy. Unfortunately, the camera stores images in
its proprietary "J6I" format. J6I is relatively easy to convert to JPEG;
however, this involves an a cycle of decompression, scaling, and
recompression which I would rather avoid.
--
Scott Ware ware_at_xtal.pharm.nwu.edu
Received on Wed Jul 14 1999 - 12:44:56 BST