Canon’s Testing a 75MP+ Pro DSLR

Started Jul 21, 2013 | Discussions thread
John Sheehy
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Re: Canon’s Testing a 75MP+ Pro DSLR
In reply to TTMartin, Jul 23, 2013

TTMartin wrote:

John Sheehy wrote:

TTMartin wrote:

hayely wrote:

This is probably 25 MP 'Triple Pixel'.

Actually that concept might not be far off.

If Canon pre-combined 4 pixels into one full color pixel, the resulting file size would be similar to the current 18-22 that Canon seems to think is optimal.

I doubt that Canon would be willing to associate their name with the color artifacts that would be incurred by such a method.

Exactly, how would Canon using in camera Bayer demosaicing be any different than what a JPG engine does (except no lossy compression or 8 bit file size) or what Nikon does when they output to a demosaiced TIFF file?

I have no idea why you said this (the grammar is confusing), but hopefully I will address whatever it was that you said.

If you take each (non-overlapping) 2x2 tile from a Bayer capture, and turn that data into 1 output pixel, what you get is quite inferior to what you would have had if you had 1/4 as many full-RGB pixels.  There will be 1/2-pixel color shifts in the red and blue channels, because the center of green is in the center of the output pixel, but the center of red and blue are offset at diagonals.  So, high-contrast edges will have half-pixel red and blue color shifts.

The only way to avoid this is to do a normal demosaicing first, and then downsample or bin the image (but binning leads to aliasing, which can be avoided with a proper downsampling).  In this latter method, there is no such thing as an exclusive 2x2 tile; such a concept does not play a role in quality demosaicing.

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