Refer to figure.
With the EVS, the flight crew are given an enhanced visual perspective of their flight environment. The EVS includes external sensors like infrared cameras to generate real-time images on the PFD or on the HUD.

The limitation of the EVS is that infrared cameras use temperature and temperature differences to produce images. This means that high outside temperatures with a large difference in the temperatures of outside objects will produce images of high resolution. Lower outside temperatures with little variation between the temperatures of outside objects will produce images of a poorer resolution.

The EVS allows for low visibility operations such as take-offs and landings to be conducted with lower minimum visual requirements. This is because the increased resolution of real-time images enhance the visibility of experienced pilots.

Note: This is fundamentally quite different from a SVS (Synthetic Vision System), as asked in a very similar looking question, No. 224897. These questions look similar but are actually the exact opposite answers due to the different systems.