CCTV has evolved rapidly over the last few years leaving quite a complex environment. Most analogue systems were classed as SD (Standard Definition) based on a comparison to the old broadcast television standard. Early digital systems used the same basic premise and operated at a resolution of 720 x 576 pixels. Next came HD (High Definition) running at 1280 x 720 pixels (known as 720p), followed by Full-HD with a resolution of 1920 x 1080 pixels (1080p). Some of the latest generation of cameras are now moving to QHD (Quad HD) with resolutions of 2560×1920.
Typically a good CCTV system will operate at least at HD and ideally Full-HD to provide the level of detail expected. There are many other factors though, such as the frame rate, compression and bit rate which all impact the overall image quality.