Conventional interlaced television systems display one low quality video 'field' 50 times every second. Combined together, two fields make a single, perceptually higher quality, 'frame'. These fields/frames are shown so rapidly that the eye is fooled into believing it is viewing a high quality-moving image, not a succession of low-resolution still images. A progressive scan DVD or projector reconstructs complete frames. The result is a more natural, stable image, with fewer interlacing artefacts such as shimmering and flicker.