OK I'm talking about two different things. Bear with me. When I change scan
resolutions from 3200 to 1600, 800, 400, 200...the scanner takes less and
less time to scan. Does this mean the scanner is ignoring or shutting off
parts of the sensor. Is the scanner in fact using 3200 to scan everything
from 3200-1601? then using 1600 to scan everything from 1600-801
etc.shutting down another row on the sensor? Am I optimizing CPU processor
time by using 3200, 1600 etc. instead of scanning at 3000 or 600? (BTW I do
just judicious amounts of USM depending on the subject matter).
Generally lower resolution will be faster of course, if that is the size
image you need for the goal, but the horizontal CCD array itself isnt much
speed factor, the hardware does that. But the vertical motor steps are a big
factor (3200 sampling stops on 3200 rows per inch is slower than 1600
sampling stops on 1600 rows per inch). And of course the larger data size is
slower to move in the port cable, that's a big factor too.
Yes, the scanner can easily scan at divisions like 3200 or 1600 or 800 dpi,
but it cannot actually scan at 3100 or 1703 dpi - it must resample then.
However, it is not just horizontal resampling that is a problem, it is also
the possible steps available where the vertical stepping motor can stop too.
The motor probably claims 2x, or 1/6400 inch steps, so for example 1/3200 dpi
is two steps per row, or four steps for row for 1/1600 dpi, which is easy,
but most other numbers like 1/3100 dpi are probably not an even motor
stepping choice, so it must do whatever it can do, like 2 steps on most rows
which is not enough, so 3 steps on a few other rows now and then, to average
it out to 1/3100 inch as requested. Not a big factor, the motor steps are
small (esp at large low resolutions), but it is one factor.
We know it cannot do 3100 dpi horizontally either, so there are different
ways it might resample horizontally, just using every second or every fourth
column is one quick way, and some do that and dont offer any other choices.
This will match the motor steps too. Or some do bilinear interpolation
horizontally, probably from the next higher integer divisor. They usually
dont specify, and overall, we can often do better resampling in our photo
editor. Like scan at 800 dpi and resample to 700 dpi yourself if necessary
(that 700 dpi would be an image size, not a printing resolution). You may or
may not see a difference, its not a huge factor, and it may depend on how
fussy you might be, and how well it does it. Note this may give different
answers on two different resolution cases.
The 2400/3200 dpi class of flatbed scanners when used at the highest
resolutions are simply not very sharp, and will normally need quite a bit
more USM sharpening than at lower resolutions. Do that sharpening last after
all other adjustments. This is going to be your biggest problem trying to
print 8x12 from 35 mm film on a flatbed. Again, some people are fussier than
others.
I realize image pixels are composed of many inkdrops. Is the number of drops
per pixel finite or is this a 0-255 computer thing? The stepper motor
"steps" 720 lines per inch to make the 1440, is this 720 number a product of
the print head "jets"?. Or is the step a multiple of 720? I realize this may
vary between printer technologies, let's just use the Epsons as an example.
What I'm trying to get at is two things. Optimizing my scan times and seeing
if there is a "sweet spot" on my printer that relates to the output DPI.
Thx
Hopefully finite. <g> But not known nor constant. The 0..255 color values
are the possible colors of the pixel (in one channel of RGB). If the pixel
color is exactly black, you do have exactly black ink, and conceivably might
need only one ink drop (or enough to fill a pixel area, but color dithering
is no issue then). If the pixel color is not exactly one of the CMYK
colors, like red, green or blue pixels are not, then several ink drops will
be needed to simulate the color, even roughly. Pixels vary in color, and
there is no such relationship that will be useful to us, nor known to us.
I'm glad we dont have to worry about it. <g>
The printer has two motors, like 1440x720 dpi. The 1400 dpi rating is the
carriage motor moving the print head horizontally. The 720 dpi rating is the
paper stepping motor moving the paper vertically. These are the locations it
can center an ink drop. The ink drop may be larger than the smallest grid we
imagine, so again, nothing is known to us. The quality setting in your
printer driver properties, 360 dpi fast draft mode, 720 dpi, or 1440 dpi slow
high quality mode, is a combination of using these locations, as best it can
do it.
The general sweet spot for printing photoquality is easy. Use one of better
quality printer settings like 1440 dpi mode, and sharpened images of 240 to
300 dpi (thereabouts, it is not at all critical that it be 240.000 dpi, 261
dpi is fine too. And 180 dpi is often pretty fair.) And of course use the
recommended photo paper, with appropriate setting for that type of paper
(which controls the amount of ink used). It's not that hard.
