Testing 8x10 vs IQ180

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timparkin
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Re: Testing 8x10 vs IQ180

Post by timparkin » Wed Sep 28, 2011 9:31 pm Etc/GMT-1+01:00

Neil Barnes wrote:As someone who's spent most of his career in imaging and signal processing of one sort and another (usually at much lower resolutions - broadcast TV) I'm watching this with interest... one thing which hasn't been discussed - and which the somewhat vague datasheet for the IQ180 doesn't specify - is exactly what is meant by '80 megapixels'. In pretty much every sensor of which I'm aware, the pixels for a colour 'block' are actually usually a variation on four pixels - two sensitive to green, one to red, and one to blue. Together that makes a colour sensitive (or monochrome, if you prefer) block but with only half the stated resolution - in both directions - in real terms.

Add to that the issue of both Nyquist limits and the comb filtering that occurs as you approach it if an optical low-pass filter is not used and it looks quite likely that the usable resolution of an 11000 wide sensor is going to be on the order of 'only' 2500 line pairs or so. On a 125mm wide 4*5 image that's roughly equivalent to 20 lines a millimetre...

As an aside - at the IBC exhibition earlier this month I got to see the NHK ultra-high resolution screen: 7680 x 4320 rgb pixels on an 85" diagonal. It is absolutely *stunning*... the camera (courtesy Ikegami) uses a colour splitter with 4000*4000 sensors - two for the green, offset half a pixel, and one each for red and blue. The system uses a 22+2 sound system (which strikes me as somewhat over the top, but which couldn't be adequately auditioned in the space provided).

Neil
Hi Neil - yes I agree, the 80Mp is only 80Mp for panchromatic light and even then the sampling is a grid and hence resolves at 30% less resolution in the 45 degree angle. If you want red detail in the 45 degree angle then you have 50% * 70% = 35% of panchromatic resolution. Hence, with nyquist/comb you have less than your 2500 (probably 2000lp).

The Bayer algorithm really muddies the waters in comparisons.

The 'screen' you talk about, is that a monitor screen? never mind... found it http://en.wikipedia.org/wiki/Ultra_High ... Television wow! nearly 100dpi on 85"!!
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Neil Barnes
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Re: Testing 8x10 vs IQ180

Post by Neil Barnes » Wed Sep 28, 2011 10:09 pm Etc/GMT-1+01:00

less than your 2500
I was being generous... :mrgreen:

Image

The quality of the image is such that when I first saw it I thought it was a damn good attempt at glasses-free 3-d TV - the detail is that good. Obviously the images chosen were those that would most emphasise the capabilities - high contrast, high colour on the whole - but nonetheless it does rather suggest that for all practical domestic purposes, 32MPixels is probably enough...

But of course, that's not why we do large format anyway, is it?

Neil

timparkin
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Re: Testing 8x10 vs IQ180

Post by timparkin » Wed Sep 28, 2011 10:32 pm Etc/GMT-1+01:00

Neil Barnes wrote: But of course, that's not why we do large format anyway, is it?
Indeed it is not.. If digital had the qualities of film (dynamic range, tonality etc) and came with a 4x5 sensor so I could use great lenses then I would be happy with only 24 megapixels I would imagine. I would probably want 40 but 24 would be absolutely fine. It would have to be proper foveon style megapixels though.. :-)

Tim
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