Canon 400D has a
10.0MP APS-C (22.2 x 14.8 mm ) sized CMOS sensor . On the other hand, Leica Digilux 3 has a
7.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Below you can see the 400D and Digilux 3 sensor size comparison.
As seen above, Canon 400D has a 1.5x Larger sensor area than Leica Digilux 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.