Adjustment of image size to fit screen

Hi,

Does anyone know how the software adjusts an image to fit the Canvass when the image size is not equal to the screen resolution of 1920 x 1080. 

For example, assuming an image of say 4032 x 2268 (ie correct aspect ratio of 16:9 but too large) does the software 'resample' the image down to 1920 x 1080 by eliminating pixels or does it 'rescale' by shrinking the image. 

Similarly for an image that is too small such as 1024 x 576 does the software 'resampe' by adding pixels or 'rescale' by stretching the image ?

Apologies if this question has already been answered elsewhere.. 

Or is some other method used ?

Cheers,

Cam