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

In article <4327B3C8.4EF71038@xxxxxxxxxxxxx>, Gordon Moat <moat@xxxxxxxxxxxxx> writes 
Kennedy McEwen wrote:

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.

I have no idea, and care less, what your particular bent or limitation is, although your comments betray lack of any scientific or instrumentation design knowledge. I assume you have some photographic knowledge, and as a consequence some experience of using commercial scanner systems. Suffice to say that I have spent over 25 years in the electro-optic imaging industry and in that time have designed, built and tested many high end imagers and scanning systems for applications you would probably never be able to contemplate. Please don't use your personal limitations as an excuse for blatant stupidity.

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.

Dead zones between pixels determine the fill factor and *improve* the resolved MTF - they make absolutely no difference to any of these calculations! As far as tests are concerned - you should revise yours: the Kodak specification for the device you referenced actually explains this effect in surprising detail for a data ***. Perhaps you will read it, but it has no effect on the fact that this device will produce a resolution of 1200ppi on an 8.5" scan width. 

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.

No, you are wriggling again! Your initial comment made no statement about optics - this was, according to you, the maximum that a 10200 cell linear array could resolve, and it is as wrong now as it was then - despite a feeble attempt to invoke optics at the last minute!

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,

Sounds like you are pulling excuses out of your ass though.

I get them from the industry that uses these things and
actually does test them.

There's the rub, bozo - I am part of that industry and have been two and a half decades and these figures are trivial to derive from basic design criteria and tolerancing.

The MTF of your example Kodak array is around 60% at Nyquist, depending on the clock rate. The MTF of a suitable optic can easily exceed 70% at the same resolution. If you are measuring much less than 35% contrast at 1200ppi on an 8.5" scan from this device then you really need to be re-examining your optical layout, because it certainly isn't high performance. As for the optical MTF at your claimed 3400ppi limit for the device: it should readily exceed 90% and thus has little effect at all on the performance of the device.

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.

On the contrary, it shows you have no idea what you are talking about. Name ONE (even an obsolete example) Kodak trilinear CCD with 10200 total cells in each line which had an optical resolution of only 3400ppi when optically scaled to an 8.5" scan width. You really are talking absurdities! Even directly at the focal plane itself, the KLI-10203 device is capable of 3600 samples per inch with an MTF of approximately 60% at that resolution (and I remind you that your allegation was not specific to this device with its particular pixel size, but to all 10200 element linear arrays!).

The number
of cells does not determine the optical resolution,

It certainly does in terms of "dpi", "ppi" parameters that you have been quoting. These terms define the SAMPLING RESOLUTION!

since all system components
affect the "optical" (or true, or actual) resolution.

I suggest you learn something about imaging system design before making yourself look even more stupid than you already do. First lesson should be what defines optical resolution and what units it is measured in. Clue: you haven't mentioned them once yet!

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.

You really don't have a clue, do you? How many swathes does this Rolls Royce of scanners make to achieve 5600ppi on a 12" scan width with only 8000 pixels in each line? Perhaps you dropped a zero, or misunderstood the numbers or just lied.


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.

You would build a scanner from such a detector without an imaging optic to project the flatbed onto the focal plane? And you *STILL* claim you know what you are talking about? You really are stretching credulity to extremes now.

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".

In which case it would be unable to yield much more than 800ppi in a single swathe at that width!

>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.

I fail to see how I could have missed this point when I specifically made reference to the condition of a single pass in the sentence you have quoted above!

Since the scanner under discussion on this thread is a single pass scanner, and the OP is specifically interested in what he can achieve in that single pass, I see no need to extend the explanation to swathe equipment.


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.

Incredible. Not only because even cheap scanners now achieve better than this, but because neither "ppi" nor "dpi" is an appropriate measurement unit for "optical resolution" in the first place!


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.

I didn't suggest otherwise - a simple optic with a single pass scan. That is what we are discussing in this thread. You are the one bringing in additional complications to justify your original mistaken advice to the OP.

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.

I suggest you look up the original patents for this "microscan" technology - you will find a familiar name in the inventors - and it was well before 1999 - although that could be around the time that the original patents expired. Even so, as the inventor of aspects of that particular technology, I can assure you that diffraction is still the limit of all optics.

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.

No, your "following posts" were full of excuses and feeble justifications (such as optics) to justify your original assertion rather than a simple statement that you were wrong.

Also, I
did apologize for not being as correct and thorough as I usually write.

No you didn't, you said "OK Maybe I should have stated that better". That does not, under any circumstances, amount to either an apology or an admission of being incorrect, let alone both.

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.

No, I browse a post first to capture the gist of the message and then respond to the specific lines I quote.

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.

Or just about any consumer grade flatbed scanner in that class of the market these days.

>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.

And what does that have to do with your allegation that they contain Sony CCDs? You are like a child pissing up a wall. 

>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.

Did you actually read what was written, Bozo? Why are you still asking about LEDs?

I did not come up with the original
calculation in that paragraph,


Why is that no surprise??

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.

TIP: optical resolution is measured at the flatbed surface, not at the focal plane - the reason for that is that only the flatbed surface is accessible for testing other than during design and manufacture and it is the only position that matters to the end user. The physical size of the CCD has no direct influence on the resolution obtained other than its implications on the optical system requirements. 7um pixels are relatively trivial to resolve optically - low cost digital still cameras work well with sub-3um pixels, albeit with limited minimum apertures, but the pixel resolution is not particularly demanding.

This should be quite amusing.

It should indeed since it is quite simple really. In terms of measurement: assess the MTF of the scanner using an ISO-12233 or ISO-16067 references depending on subject matter and determine the optical resolution at an agreed minimum MTF. Industry standard is nominally 10%, but some people play specmanship games though that is unnecessary here. You should note that this optical resolution will not be in dpi or ppi, but I leave it to you to figure what it will be, since you demonstrate ignorance and need to learn some facts.

In terms of design, just for fun, use your example of the KLI-10203 which has a nyquist MTF of better than 60% at 2MHz clock rate. Fit an IR filter, cut-off around 750nm, to eliminate out of band response. Select a 1:3 f/4 relay objective from one of many optical suppliers. Few will fail to meet an MTF of over 70% on axis at the sensor's nyquist frequency and those from the better suppliers including Pilkington, Perkin Elmer etc should achieve this across the entire field. Damping mechanism and timing to eliminate lateral post-step motion or, ideally, continuous backscan compensation of focal plane by multi-facet polygon. Result: Scan width = 8.5"; sampling resolution = 1200ppi; MTF at Nyquist for native resolution >=35% (ie. well resolved, optical resolution exceeds sampling resolution!).

MTF at Nyquist for 3400dpi should exceed 80%, based on CTE limited MTF of 95% for the detector and 90% optical MTF with 1 wavefront error at this lower resolution.

These are just figures for optics and your example detector that I happen to have in front of me at the moment - with a little searching it might be possible to obtain better. Nevertheless, 1200ppi resolution is clearly practical on an 8.5" scan width with the device you seem to believe can only achieve 3400ppi. Hardly surprising though is it - similar CCDs from other manufacturers are actually specified as 1200ppi/A4 devices!

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.

Cor, shifting goalposts really is your forte isn't it. We determine a projected resolution on an 8.5" width platform and you want to see it achieved on a 12" platform. Do you understand the ratio of 8.5 and 12? You are an idiot and I rest my case!
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
.