Pentax WG-3 has a 16.0MP 1/2.3" (6.17 x 4.55 mm ) sized BSI-CMOS sensor . On the other hand, Panasonic GX8 has a 20.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine processor.
Below you can see the WG-3 and GX8 sensor size comparison.
As seen above, Panasonic GX8 has a 8.0x Larger sensor area than Pentax WG-3. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.