The Pi camera modes
The Pi camera supports a stills capture mode, which offers the full Field of View (FOV) of the sensor (2592×1944), and a HD 1080p video mode (1920x1080p). Stills is 4:3, HD video 16:9 (wide screen) is reduced FOV ('cropped' from the center of the camera pixel array). Additonal modes were added in March 2014 = here is the full list of the supported modes :-
2592×1944 1-15fps, video or stills mode, Full sensor full FOV, default stills capture
1920×1080 1-30fps, video mode, 1080p30 cropped
1296×972 1-42fps, video mode, 4:3 aspect binned (2x2) full FOV. Used for stills preview in raspistill.
1296×730 1-49fps, video mode, 16:9 aspect , binned (2x2), full FOV (width) cropped height, used for 720p
640×480 42.1-60fps, video mode, up to VGAp60 2x2 binned with pixel skipping
640×480 60.1-90fps, video mode, up to VGAp90 2x2 binned with pixel skipping
The 'binning' modes combine 4 adjcent pixels (a 2x2 array) thus improving low light performance (as well as reducing noise). To get 90fps at VGA, half the binned pixel sets are 'skipped' during read-out (so 'almost full' FOV, using an areas of 2560x1920 out of 2592x1944).The Broadcom GPU MJPEG codec doesn’t cope above about 720P40 (it will start dropping frames, and above 45fps it just locks solid). Only Broadcom's H264 driver will support up to 720P49 and VGA@90fps.