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

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.

Check the explanation of linear and tri-linear CCDs at http://www.kodak.com/global/en/service/professional/tib/tib4131.jhtml?id=
0.1.14.34.5.10&lc=en

The entire Kodak inventory of linear CCDs is listed at
http://www.kodak.com/global/en/digital/ccd/products/linear/linearMain.jhtml and not one has the interleaved colour structure you describe.

In addition, the Sony inventory of linear CCDs is listed at
http://products.sel.sony.com/semi/ccd.html#CCD%20Linear%20Sensors nor the NEC product inventory at http://www.necel.com/partic/display/english/ccdlinear/ccdlinear_list.html nor the Fairchild site at http://www.fairchildimaging.com/main/prod_fpa_ccd_linear.htm have anything similar.

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.

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!

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.

cf. http://www.necel.com/nesdis/image/S17546EJ1V0DS00.pdf for data on such a device, where each line is in itself produced by having four real lines offset by a quarter of a pixel pitch. Guess which scanner that's in! ;-)

check out the Dalsa and Kodak web sites,

Dalsa don't make linear CCDs (in fact they don't design CCDs - all of their products are identical in form, function and nomenclature to Philips devices - even the data sheets are Philips with a DALSA sticker over the top!).

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.
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