What the 'I want more pixels' brigade don't consider!

Started Feb 24, 2013 | Discussions thread
Gerry Winterbourne
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In reply to Simon Devlin, Feb 25, 2013

Can anyone say if what follows is right or wrong?  It seems right to me but I'd like to know one way or the other.

I'll start with the old mathematical rule "don't average averages".  For anyone who doesn't understand that here's an illustration.  A dozen young men are in the gym: four are 6'1", four are 6'0", four are 5'11" - their average height is therefore 6'0".  With them are three young women of 5'1", 5'2" and 5'3" - their average height is therefore 5'2".  If we average those averages we get 5'7", which is wrong because the true average height of all 15 is 5'10".  (I hope anyone used to metric dimensions follows the reasoning).

The colour values for each pixel of our camera image file are derived by averaging the readings of a group of surrounding sensels (the averaging is more complex than just arithmetic mean but it's still an average).  The chances of one pixel mapping exactly to one dot of a printer or one pixel of a screen are remote.  The software in the printer or screen makes its own interpolation (another form of averaging) between input camera pixels and output dots or pixels.

The coarser the original averaging - in other words, the size of the camera's sensel grid - the more likely it is that the averaging error will distort the colour value of any given output dot or pixel.  So even if the resolution of the final output isn't improved by more MP its colour ought to be.

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Gerry
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First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne

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