Very interesting. Your facts support my statements rather well. My statements came from stuff Kodak said back before they started trying to get into consumer digital.
Ciao, Graywolf ---------------------------------------------------------------- ----- Original Message ----- From: Pieter Nagel <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, February 17, 2002 7:23 AM Subject: Re: Am I Really a Dinosaur? > On Sat, Feb 16, 2002 at 12:54:41PM -0000, Frits J. W?thrich wrote: > > 100 lines per millimetre is 25.4 x 100 is 2540 lines per inch. Is it OK to > > say that this could be translated to 2540 ppi, or do I miss something here? > > 100 lines per millimetre refers too 100 lines high density *and* the gaps > of low density inbetween. So you need to sample 200 lines per millimetre > to capture both the lines and the gaps inbetween. > > This is not enough. Imagine the image you are trying to scan is offset > exactly half a line with the CCD, so that each of the scanner pixels sees > exacyly half a black and half a white line. You would scan a sheet of > perfect gray. All the detail would be lost. > > So you need to sample at at least 400 lines per millimetre to get all the > detail. This is a well-known aspect of sampling theory - you need to > sample at twice the frequency of the signal you want to capture. This is > why audio CD's sample sound at 44KHz - the highest pitch the human ear can > hear is about 22KHz. > > That means we need to scan at 10160 ppi to capture all the detail from an > ideal fine-grained negative that resolves 100 lines per mm. > > Still this is not the end. This far we assumed that film grain is regular > and rectangular, like pixels. It isn't. Film grains come in various shapes > and sizes. And they are laid out in a random pattern, not a regular grid. > > Whether this means that we have to scan at an even higher resolution than > 10160 ppi I do not know. I do know that the mismatch between a rectangular > grid of even-sized CCD elements and a random array of variable-sized film > grains can yield a nasty phenomenon called "grain aliasing" at around 2900 > dpi, and that scanning at a higher resolution is the only cure. > > -- > > ,_ > /_) /| / > / i e t e r / |/ a g e l > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
