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24p, 30p / “The Film Look”

“The Film Look” encompasses a couple of factors.  How the picture is “setup” (color, “the Gamma curve” - how it handles blacks / whites and all the gradients in between) and whether the frame rate shot is progressive or interlaced.  The look comes from a term called “persistence of vision,” where the mind connects the gap between the frames, and is helped by the frame blur in the image when motion is captured.

Broadcasting is an interlaced medium in both SD and HD.  It is essentially 30 frames per second.  Each frame is drawn twice in 1/30th of a second.  Half the lines are drawn in one pass at 1/60 of a second, the other half of the picture is drawn at 1/60 of a second.  If you freeze frame a soccer ball during a broadcast, and that soccer ball is moving, you will notice jagged edges on the sides of the ball on the plane that it is moving.  This is because the camera recording the image is essentially doing the same thing, drawing the frame twice every second.

A PROGRESSIVE FRAME takes the entire image all at once.  It draws the image entirely in one frame capture, and for arguments sake, lets say the shutter opens at a 30th of a second for a 30p image.  (it’s actually quicker than that - but I won’t get into why here).  So - when shooting an action scene at 30p, the shutter is open twice as long on the camera that is shooting in 60i, where the shutter actually “Snaps” twice during the capture of that one frame.  Since the shutter is open longer, a blur is induced that is twice as significant as the blur that might be present in a 60i image, even though the same action might have been recorded and played back at the same speed.

24p is the same principle - but it conflicts with the “broadcast clock” of 30 frames per second.  24p is shooting 24 frames a second in a progressive method, where the entire image of that frame is grabbed in one pass, the shutter closes, and then the next frame is captured.  But here is where the problems begin for broadcast.  You now have six frames in EACH SECOND missing that must be accounted for, and that also can mess with recorded audio.

There is a large difference in frame rate between film, which runs at 24.0 frames per second, and the NTSC standard, which runs at approximately 29.97 frames per second.

A complex process called "3:2 pulldown" is used. One film frame is transmitted for three video fields (1.5 video frame times), and the next frame is transmitted for two video fields (1 video frame time). Two 24 frame/s film frames are therefore transmitted in five 60 Hz video fields, for an average of 2.5 video fields per film frame. The average frame rate is thus 60 / 2.5 = 24 frame/s, so the average film speed is exactly what it should be. There are drawbacks, however. Still-framing on playback can display a video frame with fields from two different film frames, so any motion between the frames will appear as a rapid back-and-forth flicker. There can also be noticeable jitter/"stutter" during slow camera pans.

To avoid this but still achieve “The Film Look”, one can shoot at 30p and get the desired frame blur, without upsetting the standardized broadcast “clock”.  All the cameras listed in the Common Cameras link on this website will shoot both 24p and 30p.  The bottom line is this - UNLESS YOU ARE TRANSFERRING TO FILM FOR THEATRICAL RELEASE OR BLUE RAY HD DISC, THERE IS NO REASON TO SHOOT 24p FOR BROADCAST PURPOSES.  THERE ARE MANY REASONS NOT TO SHOOT IN 24p, THE TWO GREATEST ARE COST INCREASE IN POST AND TIME INCREASE IN POST WITH NO TANGIBLE RESULT ON THE AIR.  I CHALLENGE YOU TO TELL THE DIFFERENCE IN WHAT YOU SEE ON THE SCREEN BETWEEN 24p AND 30p.  30p IS CLEANER WITH NO FRAME INTERPOLATION.  IF SOMEONE TELLS YOU 24p FOR BROADCAST IS SUPERIOR, THEY WANT TO BENEFIT IN PART OF THE INCREASED COSTS.