There is another variable that we have not mentioned, which is color
depth. So you have {x} [mega] pixels. But in terms of file size, each
pixel can be anything from one bit (a pure black and white bitmap with
no color or even shades of gray) to at least 48 bits (6 bytes) per
pixel. It has a HUGE effect on the file size, obviously. In principle
an 8 megapixel image could range from 1 megabyte to 48 megabytes, quite
a range (like 48:1, Duh !!).
But what about the effect on perceived quality?
20 bits per pixel is exactly 1 million colors; 24 bits per pixel is
exactly 16 million colors. Experts differ on the exact number of colors
that the human eye can perceive (and presumably it varies from person to
person), but there is universal agreement that it is somewhere between 1
million and 10 million. So once you go beyond 24 bits per pixel, you
have clearly exceeded what is necessary to achieve reproduction of all
colors that humans can perceive. Yet, all of the latest scanners go WAY
beyond this ... well up into the 40+ bits per pixel.
I find it interesting that the "old" LS-2000 scanned at 2,700 dpi (10
megapixels) and also at 12 bits PER COLOR PER PIXEL (36 bits per pixel)
(it's poor stepsister cousin, the "dumbed down" LS-30, scanned at 10
bits per color (30 bits per pixel)). And yet Nikon (and Epson) keep
bumping these numbers up, with every generation: so current products
scan 35mm film images at 4,000 dpi and 48 bits per pixel.
Sorry, but I am not convinced that the hardware manufacturers are doing
us any favors. Enough is enough, and in fact, current products really
offer almost too much, especially in the hands of dumb, naive users who
will always use the maximum settings just because they are the maximum
settings and they THINK that they are getting some genuinely additional
quality when, in fact, all that they are doing is creating a 130+
megabyte FILE SIZE whose actual quality for any real-world purpose is no
better than that of a file one-quarter of that size.
[And there is a huge impact on scan time as well]
Gour wrote:
>
> I'm (and it seems I'm not alone) confused with stuff like: "he image
> quality is not good enough to compete against a good film scanner, the
> scanning speed is extremely slow, and the effective resolution of 2400
> dpi results in 7 megapixels for 35mm material, even though the files are
> extremely bloated with about 60 megapixels."[1]
>
> From which it looks like V700 gives 2400dpi quality, i.e. 7MP but one
> needs to scan at 6400dpi in order to get those bloated files in the
> range of 60MP?
>
> [1] See http://www.filmscanner.info/en/Epson...V700Photo.html review.
>
>
> Sincerely,
> Gour
>