Multilayer sensors do a number of things that improve efficiency, mostly by eliminating cruft that’s necessary for Bayer pattern sensors. First they can lose the low pass filter, as it’s largely unnecessary because the sensor samples all colors at all points and moiré isn’t a significant concern. More importantly, the efficiency sapping color filters are gone.

The real benefit to me is the flexibility that a multi-layer sensor brings to the camera.

For those interested in the absolute best image quality it gives you a moiré free image that records the full color information at every point. Moreover, since the sensor doesn’t need a low-pass filter and isn’t doing using a Bayer pattern you get the full special resolution out of the sensor, not just a significant fraction of it.

For those who need frame rate over absolute maximum quality, you can read out a multilayer sensor as if it was a Bayer sensor and suddenly you’re looking at 1/3 of the data to process and therefore 3x higher frame rates.

Finally, for people who want to shoot monochrome, you can treat the sensor as a true monochrome sensor by summing all three of the stacked photo sites into a single monochrome output. While the market isn’t huge, there’s certainly enough of a market that Leica brought out a monochrome M, and there have been a couple of monochrome medium format backs. Though the market isn’t huge for such a feature, the amount of work necessary to implement it isn’t that big either.

With that said, lets jump back to the wild speculation on Canon Rumors rumored 75MP multilayer SLR from Canon.

Foveon, and Sigma, have always characterized a pixel as a single color photo site, even though 3 of those photo sites make up a single 3-color pixel—picture element—in the resulting picture from their X3 cameras. That’s certainly a fair way to look at it, considering that a pixel on every other digital camera is only a single, single color, photo site too.

If we assume that Canon will run with that same definition, since it makes a nice big marketable number, then the rumored 75MP camera would only have a spatial resolution of 25MP and images would be about 6124 x 4082 pixels.

A 25MP special resolution sensor actually sounds a whole lot more reasonable to me than a 75MP one does. The pixel pitch would be around 5.9 microns, instead of 3.4 microns. That’s well within Canon’s comfort zone for manufacturing, slotting in right between the 5D mark 3’s 6.25μm pixels and the 40D’s 5.7μm pixels size, and well above the 4.3μm pixels in their APS-C offerings.

From the sensor standpoint, you have comparatively big pixels, at least compared to a D800 or Canon’s APS-C cameras, which are simultaneously unencumbered by efficiency eating color and low-pass filters. That combination has the potential to be quite impressive in terms of image quality.

Then we come to the question of resolution. Canon finally unified the EOS-1 line with the EOS-1D X. I’ve always felt the split in the past was due to technical limitations more than anything else. With a single layer senor, you can only reduce the image size to reduce the amount of data being read and therefore increase the frames per second.

However, if Canon implemented a system similar to what I described above, there’s no need to break the 1D line apart again to meet both FPS and resolution targets. Never mind, current Digic 5+ processors are within spitting distance of being able to process the 300- 14-bit megapixels per second needed to support 25MP at 12FPS—the Canon 70D’s Digic 5+ is already pushing 141.4 14-bit MP/s , just  9.6 MP/s short of what’s needed.

Moreover, if you can do 12 FPS with 25MP of data, you can do 4 FPS with the full 75MP of data from reading all colors at all points. In one body, you get a reasonable frame rate at really good quality, or a high frame rates at a quality that would likely be better than Canon’s current EOS-1D X or 5D mark III.

In short, while it might not be what Canon ultimately brings to market, the rumor certainly passes my sniff test of what seems feasible. Of course this is all speculation based on a rumor reported by a rumor site. There’s no telling whether Canon will actually bring something like this to market, but sometimes it’s fun to speculate.