**Archived posting to the
Leica Users Group, 2001/04/22**

Date: Sun, 22 Apr 2001 09:04:50 -0700

References: <1120AB2026ABD211A82600A024B97137C0AD@einstein.morton.org.uk>

> Austin Franklin wrote: > > "Sorry, but my statement is perfectly correct. Having 25 years of digital > signal processing and both digital imaging and digital audio design and > development experience, I believe I understand this topic quite well." David responded: > I'm sorry, but you are quite wrong.<<<<< SNIP ETC. Austin & David: Good morning guys, seems you two have a conversation running wild "with each other" and I'm beginning to assume a bunch of us observers don't have a clue what you're talking about, let alone give a flying hoop. I also realize we can delete, however it does become tiresome deleting when it would be so much more interesting if you fella's would devote your posts to "Leica oriented" things of which you both do very well at times. And yes I know there are some other folks who know exactly what yer talking about, but I'm beginning to imagine they don't give a hoop either about what is becoming a "Technical , should I say, squabble" between two guys who are far more worldly about these kinds of things than I can ever imagine. So lads, what say you? Give it a rest? Or take it private? Over to you. Thanks. No offence guys! ted Ted Grant Photography Limited www.islandnet.com/~tedgrant - ----- Original Message ----- From: <leica@davidmorton.org> To: <leica-users@mejac.palo-alto.ca.us> Sent: Sunday, April 22, 2001 6:58 AM Subject: RE: [Leica] Film Demise > > In your original calculation you said: "Since you have to sample (scan) at > 'slightly more than' 2x the frequency you want to get, that would be ((1 x > (.5 x 5080)) x (1.5 x (.5 x 5080))) or ~9M pixels." > > What you have done here is apply the Nyquist criterion inappropriately. > > If we consider the simplified case where we are sampling a vertical grating > at 5080 DPI, then Nyquist tells us that the absolute maximum frequency that > we can reproduce is fs/2, where fs is our sampling frequency. > > Since our sampling frequency is 5080 DPI, the maximum frequency in your > example is then 2540 line pairs per inch (lppi). But notice that this > maximum frequency is in line *pairs* per inch, we have *two* pixels per > cycle, as sampling theory tells us we must have. > > However in order to calculate the maximum number of pixels in the scanned > image, you have used this *latter* figure, which is a count of the number of > reproducible *cycles* not the number of pixels. You have divided the > sampling frequency by two (in both dimensions) and used this to derive the > total pixel count. > > If you are sampling a slide 1 inch by 1.5 inches at 5080 DPI, then the total > pixel count is approximately 39Mpixels > ((5080*1)*(5080*1.5) and the maximum reproducible spatial frequency is 2540 > lppi. >