Quote Originally Posted by sanking View Post
Lenny,

Absolutely not. I am not saying that at all, and indeed am surprised at your confusion. I think we agree that some scanners deliver more real, effective resolution than others. Drum scanners, if calibrated, should deliver close to 100% of stated optical resolution. My EverSmart Pro delivers close to 95% of stated optical resolution. Most consumer flatbed scanners, Epson 4990, Epson V750, etc. deliver only about 40% of stated optical resolution. You can test this by scanning a high resolution target: you may have a pixel count of 4800 spi, but the effective resolution would be only about 40% of this, say about 40 lp/mm.

It is not a question of PMT versus CCD technology in the least. It is simply a question of understanding the fact that all pixels are not equal in terms of their detail/resolution. The concept of a "useful" pixel is only debatble if one has no understanding of what "useful" is.

Sandy King
I'll be the first to say that understanding some of this is difficult. For one thing, we all talk about scans as if we are scanning a pixel - or a bit of the image. However, they are just reads, as in a value from 1-255 in lightness darkness for three different channels of color separated light.

I do understand the stated resolution issue. It shows up clearly in the Tango, which can do 11,000 spi, yet only resolve 4000. However, you have often said that your assessment of the real resolution of the 750, for an example, was around 2000 or so (don't remember the exact #). I understand that this is quite different from pixel count, and is not the stated resolution of 5300 or whatever... However, if it is true that it is at a true optical of 2000, the 2400 you stated as the max one could get from a 4x5 would be very close.

What am I missing?

Lenny