Mega Pixels

Image resolution is typically expressed as a horizontal x vertical measurement.
So, an image resolution of 1920 x 1080 tells us that the image measures 1920 pixels in width and 1080 pixels in height.
Multiplying the two figures together gives us the second way this is commonly stated, namely as megapixels.1920 x 1080 equals 2,073,600, which is more commonly written as around 2 megapixels (MP).

Additionally,"1080p (1920×1080 progressively displayed pixels; also known as Full HD or FHD) is a set of HDTV high-definition video modes characterized by 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen vertically.

Higher the megapixel count, larger is the file size.
Instead of using image compression to reduce image size,companies now use pixel binning technology. In this technology,pixels are combined to form a bigger pixel size,which brings down the effective megapixel number and reduces the size of an image without any visible quality loss.