Hans-Dieter Oberle said:
Hi,
I connected my Epson 3200 Perfection Photo first to the USB 1.1 of my
computer. Later I added a USB2.0 interface with driver to the computer
(Windows 98 SE).
But I cannot see any speed improvement if the scanner is connected to
USB2.0
It probably seems obvious with hindsight, but improving the bus
bandwidth (eg going from USB1.1 to USB2.0) will only reduce the scan
time if the bus bandwidth was limiting the scan speed in the first
place. Usually, you can tell if this is the case because the scanner
will pause regularly during the scan while it transfers the limited data
it stores locally in its buffers to your PC memory. If it doesn't pause
then the buffer is being emptied across the bus into your PC memory
faster than the scanner can fill it up, meaning that the bus transfer is
not limiting your scan speed. In addition, even if the bus is the
limit, then the maximum gain you will get in the scan time is just the
total amount of time the scanner has paused during the scan process, and
if you then generate data fast enough to saturate even the faster bus,
the scan time won't reduce by as much as you expected.
The way to make the scanner generate data more quickly and thus force
the bus to be the primary bottleneck is to scan a wider swathe, or scan
at higher resolution or at greater bit depth and preferably all three.
So scanning a 4" width swathe at 3200ppi with 16bits per colour will
produce data 384x faster than scanning a 1" swath at 200ppi and 8bits
greyscale. USB2.0 would not make any difference to the scan time of the
latter image, but it would make quite a bit of difference to the former.
