Comparison of two types 540: effective pixels 6 million pixels operating mode with full manual function CCD sensor 1/2.5 inches LCD screen size 2.5 inches 550: effective pixels 7.1 million pixels operating mode fully automatic sensor type CCD sensor 1 /2.5-inch LCD screen size 2.0 In addition, the 540 has program exposure, semi-automatic and fully automatic exposure; the 550 only has automatic exposure, but no manual exposure mode. The rest of the parameters are basically the same.