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Line pairs and megapixels

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    MichaelMelb_AU
    12 May 2013 - 11:54 AM

    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

    Last Modified By MichaelMelb_AU at 12 May 2013 - 12:03 PM
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    12 May 2013 - 11:54 AM

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    redsnappa
    redsnappa  111911 forum posts United Kingdom
    12 May 2013 - 3:23 PM

    That's the geeky bit out of the way we can now forget it and be creative.

    Paul Morgan
    Paul Morgan e2 Member 1315152 forum postsPaul Morgan vcard England6 Constructive Critique Points
    12 May 2013 - 7:55 PM


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

    And your point is ? Smile

    MichaelMelb_AU
    12 May 2013 - 9:14 PM

    Please point to any factual or logical mistakes if you see them Smile And if now interested - why bother?

    Last Modified By MichaelMelb_AU at 12 May 2013 - 9:15 PM
    strawman
    strawman  1022006 forum posts United Kingdom16 Constructive Critique Points
    12 May 2013 - 9:39 PM

    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

    Helpful Post! This post was flagged as helpful
    MichaelMelb_AU
    13 May 2013 - 12:48 AM

    Try to Google for Leica M monochromeSmile

    strawman
    strawman  1022006 forum posts United Kingdom16 Constructive Critique Points
    13 May 2013 - 11:47 AM

    Ah so they did make it. Sounds like a lovely idea, sadly outside my budget at the moment Smile

    MichaelMelb_AU
    13 May 2013 - 1:29 PM

    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?

    Last Modified By MichaelMelb_AU at 13 May 2013 - 1:30 PM
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