How does demosaicing work in Fujifilm's new sensor for the X Pro-1?

Question

Fujifilm has an innovative new sensor layout for the just-released X Pro-1 camera, which they say is "inspired by the natural random arrangement of the fine grains of silver halide in film":

Since the arrangement is more aperiodic (less repetition), it's unlikely to cause moire artifacts (which occur when there's a misalignment between a pattern on the sensor and stripped pattern in the recorded image). This lets Fujifilm skip the low-pass AA filter, which traditionally adds blur to combat this issue.

They add "Also the presence of an R, B and B pixel in every vertical and horizontal pixel series minimizes the generation of false colors and delivers higher color reproduction fidelity."

How does conversion of this type of RAW image work? Is it essentially like Bayer demosaicing algorithms but a little more complicated, or does it require different approaches altogether?

In the latter case, it seems like there's a large risk that third-party RAW conversion support will be unavailable or rare, but if the same basic algorithms can be used I expct it to be less of a problem.

Other than that software support issue, are there potential downsides as well as the advantages Fujifilm claims?

Answer 1

This isn't the first camera to deviate from the standard RGB bayer layout, there have been cameras released with cyan as a fourth colour (replacing half of the green filters) as well as a fourth clear filter for better luminance resolution and low light ability. Fuji have also experimented with octagonal sensors and split dynamic range sensors so know a thing or two about nonstandard demosaicing processes!

The layout Fuji have chosen will actually make demosiacing easier, you could probably get away with a linear interpolation if you had to.

More complex demosiacing algorithms all try to make guesses about which values are likely to remain constant between adjacent pixels, giving you an extra sample for free. Exactly the same principals can be applied to the Fuji arrangement. However the implementations will need to be tweaked to take into account the swapped red and blue filters.

However these tweaks are unlikely to be implemented in the popular RAW converters such as Lightroom due to it's niche market so users of the camera will probably be stuck with whatever software Fuji come up with for some time...