traditionally interlaced video, in which one-half of the scan lines of each frame are broadcast at a time). Most simply, the frame rate can be doubled by simply displaying the same broadcast image twice in rapid succession, as is done with movie projectors (which display each frame of 24 fps film two or more times) – either displaying each field twice or alternating fields. Alternatively, this can involve motion interpolation, where rather than displaying the original fields twice, creates interpolated images between the original frames. This may be combined with deinterlacing, converting the image to progressive scan (attempting to create a full picture from the two half images). Higher refresh rates, while they reduce flicker, may cause other problems. Simply redisplaying the fields may cause judder, particularly on fast moving images, as the image is displayed repeatedly in the same location, rather than moving smoothly. Conversely, interpolation (which avoids judder and may create more fluid motion than in the original video) can instead cause blurring, particularly visible on fast scrolling text. See motion interpolation for further discussion. See also Flicker (screen) Flicker fusion threshold Notes Pulse Width Modulation Effects of PWM used in LCD brightness control Display technology Television technology