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Line pairs and megapixels


12 May 2013 11:54AM
In theoretical discussions rotating around film photography, line pairs per millimetre (LP/mm) is mentioned as resolution unit. The modern image resolution unit is megapixels. To make any sense of such discussions, resolution units translation is needed. Most often line per mm is translated into to pixels (white and black) in either vertical or horizontal direction. Let's see how this is described by Image Engineering site:
As a line pair is always a black and a white line, the maximum resolution one can achieve is 1/2 LP/pix.
While completely correct in general terms, this definition becomes very limited if one takes into consideration the physical nature of modern sensor. What I mean here, because of colour filter array use, a dot on a black or white line in the image is not formed by a single pixel but ( for example in case of a simplest Bayer pattern ) by a 4-pixel block, or 2 pixel vertically and 2 pixels horizontally. Separate case present diagonal lines - here we will have 6 pixels responsible for a pair of lines.
So, even with very optimistic approach to unit translation, the definition should rather look like:
In practical terms maximum resolution one can achieve is 1/4 LP/pix.
Taking decent B&W film resolution at about 50 LP/mm we have (24*50*4)=4800 pixels vertically by (36*50*4)=7200 pixels horizontally. This gives us an optimistic estimate of 34.56 Mp per full-frame Bayer sensor - which "accidentally" comes very close to Nikon D800 36,3 Mp count. Wink

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redsnappa 12 2.0k United Kingdom
12 May 2013 3:23PM
That's the geeky bit out of the way we can now forget it and be creative.
Paul Morgan e2
13 16.1k 6 England
12 May 2013 7:55PM

Quote:In practical terms maximum resolution one can achieve is 1/4 LP/pix


And your point is ? Smile
12 May 2013 9:14PM
Please point to any factual or logical mistakes if you see them Smile And if now interested - why bother?
strawman 11 22.0k 16 United Kingdom
12 May 2013 9:39PM
I think it can be said the B&W film does manage in some cases to achieve the resolution you mention, but not too often, up the ISO and the grain size gets involved it all gets messy. In reality I believe the calculation is fairly complex because you are covering the Bayer method of generating colour which is not quite the same as the shade resolution as you can use the pixel by pixel data plus interpolation. And then when talking about Bayer sensors you do need to factor in the anti-aliasing filter (if it has one) as that can limit the captured resolution, as will in some cases lens aberrations diffraction etc.

There has often been idle talk of a monochromatic sensor coming from Leica but to my knowledge it never turned up.

I just prefer to be amazed at what modern lenses and cameras can do Smile
13 May 2013 12:48AM
Try to Google for Leica M monochromeSmile
strawman 11 22.0k 16 United Kingdom
13 May 2013 11:47AM
Ah so they did make it. Sounds like a lovely idea, sadly outside my budget at the moment Smile
13 May 2013 1:29PM
B&W film is still readily available for the one who needs it. And I bought an old goodie EOS500(no D!)
for just 15$A ( roughly 10 pounds). Perfect for my 50mm f1.8 EF lens. It may be not Leica - great with ISO800, but at ISO100 it's second to perfect. Get the drift?

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