Motion tests

What the test shows

Most projectors, DLP included, keep each frame on screen until the next one arrives. When your eyes follow a moving object, they keep moving while the frame stands still, so the picture smears across the retina. The longer a frame is held, the wider the smear: at 960 px/s an object moves 16 px per frame at 60 frames a second and 8 px at 120, and that is roughly how wide its edges blur. What counts is the frame rate, not the refresh rate: 60 fps shown on a 120 Hz output still blurs like 60 Hz, which is what the Every 2nd frame lane shows at 120 Hz. Faster pixels can't take the blur below this; only more frames a second or a shorter flash of each frame can.

Film adds a second problem. 24 frames a second don't divide evenly into a 60 Hz output, so frames are held alternately for 3 and 2 refreshes (3:2 pulldown) and motion goes in uneven steps. At 48 or 120 Hz every film frame is held equally (2:2, 5:5): the steps are even, but there are still only 24 of them a second, which shows as stutter on slow pans. Motion interpolation (MEMC) in the projector computes frames in between: motion gets smooth and, with more frames a second, sharper to follow, but fine detail can break up and moving edges may get halos.

How to watch

Show the page on the projector from a PC or media player, full screen, at native resolution and at the output refresh rate you want to test, and sit where you normally watch. Speeds are in pixels of the actual screen per second (1x is 120 px/s). The line under the pattern shows the measured refresh rate, the step in pixels per frame, the speed that results and the dropped frames over the last 10 seconds. A dropped frame looks like a twitch: if the counter goes up at the same moment, the twitch comes from the computer, not the projector. On a Mac turn on High precision in Settings: without it macOS may slow the graphics down between frames, and motion stutters although nothing is dropped.

Modes and objects

The menu at the bottom left picks the mode, the buttons next to it the object: a steamboat, a snail or a train. They are the same objects as in our MEMC test clips: the paddle wheel turns, smoke comes out of the funnels, waves and foam run past. Any object works in any mode, and it is sized to the height of its lane.

Frame rate shows the object four times at one speed: standing still at the top, then updated every frame, every 2nd frame and like 24p, 24 times a second in the cadence your refresh rate gives. Compare the small details (portholes, the SPYKEVISION lettering, wheel spokes) with the object standing still: the difference is the motion blur, and the lower lanes add the judder of a lower frame rate. The wheel, smoke and waves update with their lane, as in real 24p video.

Cadence: the object moves slowly, 1 to 4 px per frame, where uneven steps are easiest to see. The upper one always moves evenly; the lower one moves in the cadence you pick: steady, 3:2 (24p at 60 Hz) or 2:2 (24p at 48 Hz; at other refresh rates the lane shows the frame rate it gets). Turn the projector's MEMC on and off: with it working, the lower object should move as evenly as the upper one, and the smoke, spokes and lettering give away interpolation artefacts.

Pursuit shot: one large object with a ruler under it that moves with it: a short tick for every frame of travel and a long one every N frames (set in Settings). The train runs with three cars here, with window frames, car numbers and lettering in three sizes. Pan the camera along with the object at its speed with a shutter of a few frames. When the panning matches, the ruler comes out sharp, and the smear on the edges measured against the ticks shows how many frames' worth of travel the projector blurs.

The default background is the one from our clips: dark blue vertical stripes, which show at a glance whether the object moves evenly. Settings also offer dark, grey and a starry sky; on a projector the brightness around an object changes how visible its trail is. For colour fringes on moving edges use the Rolling Buffer Test, for the rainbow effect the Rainbow Test.

Mouse: click the pattern to pause, double-click for fullscreen. Keys: left / right arrows direction, M next mode, 1 2 3 the object, + / - speed presets (in the Cadence mode, the step per frame), space pause, F fullscreen.