Re: Multi-sampling and "2400x4800 dpi" scanners

Kennedy McEwen wrote:

> In article <43275103.1B9077A7@xxxxxxxxxxxxx>, Gordon Moat
> <moat@xxxxxxxxxxxxx> writes
> >Kennedy McEwen wrote:
> >
> >> In article <4325DEBE.E10868F9@xxxxxxxxxxxxx>, Gordon Moat
> >> <moat@xxxxxxxxxxxxx> writes
> >> >
> >> >Actually, many linear CCDs are 8400 or 10200 cells (pixel sites), though
> >> >divided by three to give each colour Red, Green, and Blue. Kodak have some
> >> >nice White Papers on these.
> >> >
> >> Not generally - colour linear CCDs used in scanners are generally
> >> tri-linear. Each colour is a separate parallel line of CCDs, they are
> >> not divided.. . . . . . . Now, I am not saying these devices don't exist, but
> >> I would like some
> >> pointer as to where you are getting this information from since it is
> >> not from the Kodak or Dalsa sites you reference, and more likely to be a
> >> misunderstanding on your part. Whilst there may well be colour
> >> interleaved linear CCDs these are certainly not used on any commercial
> >> scanners that I am aware of.
> >
> >Okay, maybe I should have stated that better. So I will give you one to find
> >and read about. That is the Kodak KLI-10203 Imaging Sensor. It is correctly
> >termed a 3 x 10200 imager, so I apologize for not being more thorough in my
> >description of it.
>
> The KLI-10203 is a tri-linear CCD (check the FIRST line of the data
> ***!) - *each* of the lines is 10200 cells long and *each* of the
> lines is a separate colour - no interleaving. So, contrary to your
> claim that this could only resolve 3400ppi, because it has 3 colours in
> each line, it can 5100cy/length. Without optical scaling it resolves
> 3600ppi, with optical scaling (as would be used in a scanner
> application) this can be set to match whatever the scanner width is - on
> the 8.5in flatbed scanner configuration that the OP is referencing, it
> would produce around 1200ppi.

It figures that an amateur mathematician hobbyist would have never used a high end
scanner. Theories disappear when you actually are able to use devices that have
these installed in them. There are no imaging chips with 100% efficient cell sites,
nor any without a dead zone between cell sites of greater than 1 µm in size. You can
calculate all you want, but actual tests of this gear are far better than theory.

>
> >
> >> >So in theory an 8400 element linear CCD should be able to resolve 2800
> >> >dpi, and a 10200 element CCD should be able to do 3400 dpi.
> >>
> >> A colour CCD with a total of 8400 elements would only be capable of
> >> resolving 2800 colour samples across the A4 page - somewhat better than
> >> 300ppi - whilst your 10200 element colour CCD would only be capable of
> >> 400ppi! The real requirements for flatbed scanners are *much* higher
> >> than these!
> >
> >If you could figure out what scanner uses the KLI-10203, then you might be
> >surprised at your statements.
>
> I don't think so, mainly since the statement is based on *YOUR* figures
> that the 10200pixel CCD is only capable of 3400ppi!

Not the CCD, but the system in which it is installed. You cannot have a flat bed
scanner without optical components. Those optical components will limit the total
system resolution. In fact, that resolution is based on actual tests of scanners
with that exact 10200 pixel (3 rows to be specific) imaging CCD. I don't pull these
numbers out of my ass, I get them from the industry that uses these things and
actually does test them.

> Perhaps you see now
> why it was ridiculous? And before you wriggle further - KODAK DON'T
> MAKE A 3400PIXEL LONG TRILINEAR (10200 TOTAL CELLS) CCD AND NEVER HAVE!!

That statement shows your level of ineptitude, and lack of reading comprehension.
The 3400 dpi figure is the OPTICAL resolution, not the size of the file. The number
of cells does not determine the optical resolution, since all system components
affect the "optical" (or true, or actual) resolution. In fact, the current best flat
bed actual optical resolution is 5600 dpi across the entire 12" by 17" scanner bed,
and those two particular scanners used an 8000 element tri-linear CCD. That very
simple fact should tell you that the optical resolution is not simply a factor of
the imaging chip construction.

>
>
> An A4 flatbed scanner, as the type under discussion in this thread,
> means a scan width of at approximately 8.5"; 10200 pixels across that
> distance yields exactly 1200ppi - no division by three because the
> colours are on three separate lines of 10200 cells *each*, not
> interleaved on a single line as you suggested.

Three rows of 10200 cell sites each, 30600 in total . . . did you not read my second
reply, or are you just trying to be dense on purpose. Further information is that
the particular example I chose, the KLI-10203, has a physical dimension of 76.87 mm
by 1.6 mm . . . seems to me that is much smaller than 8.5" across, unless you are
using a different metric to english conversion.

Just to update you a little bit, the smallest bed width in which the KLI-10203 is
actually installed is 305 mm, or about 12". The length of that particular smallest
scanner is 457 mm, or about 18". Much larger than A4. In fact, I don't know of any
true high optical resolution scanners that are A4 sized, nor do I know of any A4
sized flatbeds that use the KLI-10203. Maybe I should have picked a lesser imager
for this discussion.

>
>
> >Just to give you a hint, it is only available in
> >a few high end products. The lowest spec (and lowest cost) of those does 3200
> >dpi true resolution. That is across the entire bed, and not just down the
> >middle.
>
> Not across the full A4 width o a single pass it isn't. To achieve
> 3200ppi resolution requires a scan width of no greater than 3.2" -
> around a third of the width of the flatbed under discussion!

What you are missing is that not all scanning systems in flat beds use a "pass" in
one direction method of scanning. There are XY scan and XY stitch, and variations of
that to scan the entire flat bed area. Send off an 8" by 10" transparency to
Creo/Kodak and ask them to scan it for you . . . of course, I should alert you that
they only offer that for potential customers who are serious about buying their
products.

>
> >
> >> An A4 scanner with a 1200ppi capability has a tri-linear CCD with round
> >> 10,500 cells in *each* line ie. a total of more than 31,000 cells. A
> >> 4800ppi full page scanner requires a CCD with more than 42000 cells in
> >> each line, a total of over 125,000 cells.
> >
> >Okay, just to through out some numbers, and then you can do calculations, or
> >whatever. Using the KLI-10203 again, the cell sites are 7 Î*m square pixels.
> >There are 3 rows of 10200 cells each, so 30600 total cells. Row spacing is 154
> >Î*m centre to centre. There is no sideways offset of cells in each row, and the
> >spacing allows a processing timing gap of 22 lines.
> >
> And how much of that determines the ppi of the final application? Hint
> - nothing, but now we know you can read a data ***!
>
> So where does *your* figure of 3400ppi limitation for this particular
> device come from - apart from your initial misreading of the data?

Actual test of high end scanning gear. True optical resolution. In fact, the very
best can do much better than 3400 dpi, though all of those use a different imaging
chip. Many of those use an 8000 element tri-linear CCD, and add better optics,
active chip cooling, and even more precise positioning. Try Creo EverSmart line,
Dainippon Screen Cezanne, and Fuji Lanovia Quattro. Actually, the Fuji Lanovia
Quattro has a 10500 Quad-linear CCD for colour scans based on their super CCD
technology, and adds a single line 16800 element CCD for copydot usage (do I need to
explain copydot scanning?), so that particular Fuji (and their FineScan 5000)
actually do better than 5000 dpi across the scanning bed. I could also mention
Purop-Eskofot, but they are not easy to find.

Just to give you a very simple explanation, that 1200 dpi figure you calculated
would be very close to the actual in a system in which very simple optics were used
in the scanner. In fact, around 1999, when these chips were new, that was nearly the
limit in almost any flat bed scanner. Since that time, scanner optics have improved,
and positioning of optical elements has improved. Those improvements are expensive
to implement, and why you only see them at the high end. However, those improved
optics and better ways to move the optical elements help that family of circa 72 mm
CCDs achieve better than 1200 dpi true optical resolution, and even high
interpolated resolution.

>
>
> >
> >Dalsa bought out the Philips imaging chip business, though they kept some
> >engineers and other workers. Is it still possible to buy imaging chips directly
> >from Philips?
>
> Certainly was the last time I tried, which I believe was earlier this
> year although time flies.

Okay, glad to see you got something right, and nice to hear Philips chip division is
still plugging away. ;-)

>
>
> >Anyway, they do have some nice information on chips on their
> >website.
>
> They do, but *none* of them are linear arrays and making inferences from
> the limitations of 2-D arrays, particularly colour arrays, on linear
> devices is misleading at best and completely deceptive at worst. For
> example, DALSA's biggest array is only 5344 pixels along the largest
> axis - but you wouldn't interpret that as state of the art for a linear
> array!
>
> >>
> >> Interleaved colours (by Bayer masking) is common on two dimensional CCDs
> >> (indeed, Bayer was a Kodak employee!) but this is unnecessary in linear
> >> devices. I suspect that you are confusing the two.
> >
> >Okay, to be more specific, each row on a linear CCD has a colour filter over
> >it.
>
> Precisely - but that isn't what you wrote last time! You stated that
> the 3 colours resulted in a resolution of only one third of the number
> of pixels in the line.

I misstated it, though hopefully it is more clear in the following posts. Also, I
did apologize for not being as correct and thorough as I usually write. Interesting
that your earlier tone is different . . . almost makes me feel that you respond in
line prior to reading everything, which would be careless in the event that is the
situation.

>
>
> <snip the millenium prize for rewording the previous post!>
> >
> >Okay, so I don't recall mentioning interleaving, but interpolation was
> >mentioned, though only for upsizing or downsizing to change resolution. The OP
> >wants to use what he thinks might be extra resolution in one dimension of the
> >specifications for his scanner.
> >
> No he doesn't - or at least that isn't what he has asked about. He is
> interested in using available samples in two axes that do not provide as
> much resolution as he would like as a means of achieving improved signal
> to noise at a lower resolution.
>
> The CCD in his case is similar to the NEC uPD8880 device, a trilinear
> array with 21360 cells in each colour, capable of producing 2400ppi
> across an A4 platform. Each of the colour lines comprises two rows of
> 10,680 cells capable of reproducing 1200ppi on the flatbed, but offset
> by half a pixel pitch to create a 2400ppi sample density. In addition,
> the scanner motor is capable of moving the scan head in 4800ppi steps,
> further oversampling the original pixels. He is interested in using
> these oversamples optimally for signal to noise improvement at 2400ppi
> and possibly as low as 1200ppi rather than have some of their
> information being used to achieve resolution which is already
> compromised by the optical system of the scanner.

Okay, so sounds like a UMAX, Epson, or maybe a Microtek.

>
>
> >An exception to colour filtering is in many Nikon film scanners, since they use
> >coloured LEDs as a light source. I would suspect those are Sony imaging chips
> >in those Nikon scanners.
>
> You would be wrong.

Big Fluffy Dog . . . I have run through enough broken Nikon scanners to avoid them.
They are poor production choices. Great shame they are not as well built and rugged
as their top level cameras.

>
>
> >While many do like the LED approach, it is interesting
> >to note that is not done in any high end scanning systems.
>
> Wrong again! It is exactly the process used in high end film scanner
> systems - the difference being that the LEDs are replaced with colour
> lasers to achieve a higher intensity and thus a faster throughput.

I don't recall Imacon using LEDs . . . okay, just checked and all current models are
not LEDs. Or perhaps you actually think a Nikon film scanner is a high end product?
Put any Nikon scanner into a high volume environment, and they break just a bit too
soon to take them seriously for producing income. It is better to spend a bit more
and get high resolution with high volume and little to no downtime. Now to be just a
little critical of Imacon, they did have some units in the recent past that were a
little more troublesome than should have been expected, though their service is very
fast and efficient (a statement few would make of the current situation at Nikon
USA).

>
>
> >I doubt it is some
> >patent issue, and more likely that a single light source provides a more
> >predictable scanning operation in regards to colour accuracy over the life of
> >the scanner.
> >
> >Anyway, I apologize for not being more clear, a 10200 linear CCD should be
> >correctly termed a 3 x 10200 element linear CCD. Regardless the resolution is
> >still limited by the physical size of the cell site, the scanner optics, and
> >the accuracy of movement of the imaging components within the scanner. A linear
> >image sensor with a single array of 1000 photosites of pitch 10 Î*m would have a
> >resolution of 2540 dpi (1000 / (1000 x .01 mm x 1"/25.4mm)). If that sensor
> >were used in an optical system to image an 8" wide document, then the
> >resolution in the document plane would be 125 dpi (1000 pixels / 8"). If we
> >consider the 7 Î*m cell size for the KLI-10203, for example, then we can
> >estimate for that imager.
> >
> You don't need to go round the houses - the calculation is trivial.

The calculation is from the spec ***, and used as an example. It was also posted
as a lure to see how you would respond. I did not come up with the original
calculation in that paragraph, I merely transposed it. Anyway . . . . .

> An
> 8.5in scan width with 10200 cells per line (no matter what the optical
> system or the cell size or pitch is) results in 10200/8.5 = 1200ppi.

Why don't you tell me how 3400 dpi measured optical resolution is possible using a
circa 72 mm 10200 element tri-linear CCD. This should be quite amusing. Oh, and just
for fun, use that 12" by 17" bed as your explanation basis. The device is the Creo
iQSmart1, in case you have not figured that one out yet.

What I think you are missing is that "line" is a term for the line of the CCD, which
is about 72 mm, not 8.5". I am sure you have read about many scanners with a "sweet
spot" near the centre of the flat bed. This is due to limitations in movement of the
optics, mirror, CCD platen, or any other components that move to allow scanning to
occur. Low end and mid range systems, of which I am certain are your primary
experience, have very simple and very limited imaging components. Better control of
optics, movements, and signal processing will improve results.

Come on Kennedy, I thought you were smarter than this. See this as a challenge, and
then figure out why high end scanning gear works so well, and costs so much. I judge
scanners based on actual tests performed to determine true optical capability, and
not just resolution. Good design control will also help colour accuracy and Dmin to
Dmax performance. Read too many Epson, Canon, UMAX, MicroTek, Minolta, or other low
and mid range gear spec sheets, and you can easily be fooled into thinking these
cheaper devices are much better than they really perform. At least the lower cost
film scanners do better than the low cost flat bed scanners.

Ciao!

Gordon Moat
A G Studio
<http://www.allgstudio.com>

.