2: X-Trans Color Filter
3: L/R Light Interception Filter
4: Phase Detection Sensor / Green Filter Pixel
The 1/1.5-inch sensor has BSI pixels and integrates phase detection pixels for faster AF. Fijufilm says that an optical LPF is not necessary for its X-Trans sensors (both 1/1.5-inch and APS-C ones):
"X-Trans CMOS II adopts an original color filter array with a highly random pattern, eliminating the need for an optical low-pass filter (OLPF), which is used in conventional systems to inhibit moiré at the expense of resolution. This lets the sensor directly capture the high resolution performance of the FUJIFILM X20 lens. Also exploiting the enhanced performance of the EXR Processor II, Lens Modulation Optimizer (LMO) factors are calculated to compensate for aberrations and diffraction blur that occur when light passes through the lens and then are applied to produce images with amazing sharpness."
The noise of the new sensor is said to be reduced by 30%, improving the low light SNR.