1 - Parameters
1.1 - MP
to crop images and zoom in on certain areas. This is quite possible with 20-megapixel, 13-megapixel and even eight-megapixel sensors without a huge reduction in quality, but isn’t the case with HTC’s four-megapixel unit.
1.2 - Sensor size
f-number, necessary focal length, and its crop factor.
A larger sensor has more area for the light to fall on, equating to a greater ability to gather the light, assuming the megapixel count stays the same. The size of a smartphone sensor is typically given as a fractional number in inches (eg. 1/2.3”, 1/3.06”), which may appear to give the diagonal dimensions of the sensor, but actually doesn’t. Instead it refers to a type of sensor, with a diagonal size around one third smaller.
1.3 - Pixel Size
Sensor size is useful for getting an idea of how much space in the smartphone camera module is consumed by the sensor, but less useful for gauging total light collection. Pixel size: direct measure of how large the individual photodetectors are in the CMOS sensor. Pixel size for smartphones fits into a narrow range between one and two micrometres (or microns, abbreviated as µm) in either the horizontal or vertical direction. Again, the larger you go, the more light each pixel can collect.
1.55-micron pixels that do well in low light. These are larger than normal pixels, and therefore can capture more light for stronger indoor photography.
1 metre is equal to 1000000 um (um = micrometres)
the large pixel size really does improve low-light performance