David Heath |
December 22nd, 2010 04:38 AM |
Quote:
Originally Posted by Jan Crittenden Livingston
(Post 1600542)
there is no line skipping being used. It uses an optical low-pass filter to resolve the aliasing and moire that is typical from high count imagers.
|
My understanding is that the OLPF is arranged to cut off the detail at around the detail level of an HD image - far less than the finer detail of the native chip.
There is no question that the OLPF will largely resolve the issues of moire/aliasing (it will), but this is quite independent of whether the chip is read in total or via line or pixel skipping. Saying that it uses an OLPF, and has little evident moire/aliasing, says little about how the chip is read.
The AF101 is reckoned to have about the same native sensitivity as a 1/2" 3 chip camera, with comparable technology. If every photosite was being read, every frame, the expectation would be that the sensitivity would be (should be) much higher. Technically, the AF101 results are in line with not every photosite being read or used in every frame readout - line skipping or pixel skipping.
If what is basically a still camera sensor is used, the alternative to line or pixel skipping is to read out the entire sensor (all 12.4 million pixels) every frame, deBayer, then downresolve with software filtering. The technical challenge of doing such in terms of complexity, power requirements, heat dissipation etc shouldn't be underestimated, and it is extremely difficult to see how they are overcome in a camera of this price, consuming relatively little power? From a designers point of view, far easier, sensible and more cost effective to pixel skip and deal with the aliasing with an OLPF.
If "line skipping" isn't used, what about other forms of pixel skipping, such as in blocks of four? It would be interesting to point the GH2 at a zone plate in 40fps burst mode, and see what the patterns reveal. That mode restricts resolution to 4 megapixels, and is likely to use the same principles that the AF101 does - but since the GH2 doesn't have the OLPF of the AF101, the alias patterns should be unaffected and tell us more about exactly what's going on.
|