Noons said:
Can you explain that a bit more, David? First time I heard
the "offset CCD" and why would it be relevant? Any urls
wheer I can read about it? TIA
The Epsons use two adjacent half-resolution CCD lines that are offset by 1/2
the pixel pitch; each pixel is "seeing" an area much larger than the nominal
pixel size, so the value it reads out is an average over a larger area.
Basic sampling theory tells you that you want point sampling (of a low-pass
filtered signal) for optimal performance, so Epson's "4800" ppi is a long
way from optimal. But there is still some response at higher frequencies
that can be used by aggressive sharpening.
Kennedy McEwen has explained the math that describes what happens in detail
in this newsgroup in the past, so Googling for his messages should turn up
something.
IMHO, the 4990 does a credible job of handling colour negatives.
Yes, that was my experience with the 2450 as well.
For slides, I agree 100% with you. Don't ask me why it should be
so, I don't know enough of scanning theory to debate it.
Just my feelings based on my results, no elfs.
The "oversampling" seems to work to reduce grain aliasing in negatives, it
seems. There really isn't much more than 2000 ppi of real information on
film anyway, so the 4800 ppi Epsons should be getting very close, even
though the apparent resolution is only a fraction of that.
IMHO, one should always buy an Epson first, and then think about a real
scanner if one isn't happy. The 4990 is the same price as I paid for my
2450, and that was money well spent since I learned about scanning first
hand, and knew what to look for when I got test scans done. I'm hesitant to
actually say that, though, because there are people who claim that they are
much worse than even I think they are. I think you ought to be able to get a
nice 6x enlargement with no complaints, but there are people who claim 3x is
the limit. So there _may_ be sample-to-sample variations in the beasts.
Anyway, a real film scanner still will look quite a bit better at, say, 9x
and over. But the number of people who need that should be a lot fewer with
the 4990 than with the 2450.
David J. Littleboy
Tokyo, Japan