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Sometimes when I pause DVDs the image is sharp, but in most cases, it is blurry. Obviously the film itself isn't blurry. Is the blurriness actually in the film strip or is it an artifact of the DVD pause process? In the strip below only one of the frames has any blur:

wizard strip

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    Side note: If the "blur" you're talking about in the above image of film is that the top two frames are out of focus, that's an issue with how the image of the film was made (the top of the film stock was not in focus; note the numbers along the film perforations in the upper right are out of focus as are the film perforations themselves). It's not an issue with the images that are actually on the film. Note that there are also considerable artifacts in the above image as a result of JPEG compression, which are visible throughout the image. – Makyen Dec 6 '17 at 6:43
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    Are you asking about purely the effects of interlacing, where you can see the artefacting in a motion-free shot, or actual blur, in fast action? The causes & visible results are different. – disassociated Dec 6 '17 at 7:42
  • I think a better description of the blur (possibly a photo or screen capture) might help to narrow down the actual reason. While interlacing is one possibility I'm not absolutely sure that is what you saw. – Octopus Dec 7 '17 at 4:43
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Interlacing

Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured at two different times.

TL; DR

...when you pause an interlaced video, it actually shows you two fields at once, each captured at slightly different times. I guess you could call it an exaggerated form of motion blur, but in some cases, it's actually the second half of one frame mixed with the first half of the next frame, interlaced together. That is why the image looks blurry when you pause it.

Longer....Per Reddit

This is a result of interlaced video. It's mostly limited to older formats, but you can still see it sometimes on Netflix or Hulu if the source of the footage is old enough, of sometimes when you pause the local news (even in HD) or certain other video sources.

So, what is interlaced video? As others have pointed out, film usually runs at 24 frames per second, but back in the 1950s when television standards were being created, the engineering limitations of the time meant that the frame rate of video had to match the electrical grid's refresh rate, which in the US was and still is 60hz, or 60 cycles per second.

Okay, that's great, right, 60 frames a second, then? The problem was that the technology of the time couldn't process or transmit an entire frame's worth of information that often, and besides, filmmakers were already familiar with the 24 frames per second rate of film. So they compromised and developed a system that captured half of a frame 60 times a second.

So, okay, no big deal, that works out to 30 frames a second, right? Nope. Video cameras of the time couldn't buffer anything, so it literally sent half of a frame 60 times a second, and televisions displayed half of a frame 60 times a second. Because time waits for no man (or camera), each half-frame captured it's own separate point in time. These half-frames are called fields, each composed of alternating horizontal lines. Of course, if one field contained the top half of a frame and the other contained a bottom half of a frame, the resulting moving image would always look like it had a slight tear in the middle, and the screen itself would look a bit like a flip book, so, the odd numbered fields contained the odd numbered lines of the image, and the even fields contained the even numbered lines of the image.

Video cameras long ago developed the ability to capture an entire frame at once, but video formats and televisions in wide use couldn't display a single frame at a time until the 2000s(!). This meant that Hollywood films and other content that was captured using whole frames were still copied to VHS and even DVD using fields instead. Later-era DVDs and early HDTVs were able to use a feature called Pullup/Pulldown to take the original 24 frames of a motion picture, chop them up in to a set of 60 fields in order to be written correctly to a DVD, and then put back together and displayed as 24 frames by the DVD player. It wasn't until Blu-ray that true progressive frames rather than fields were actually native to the entire technology stack (media, player, TV).

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    Is there any chance you can summarize the essential parts of this giant quote block somehow? – Napoleon Wilson Dec 5 '17 at 21:30
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    @Malvolio Um, don't tell it to me, tell it to the readers of the answer. – Napoleon Wilson Dec 5 '17 at 22:47
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    Note that colour TV complicated matters, forcing the US to 29.97 frames per second. PAL swapped to 25 instead. See, for instance, youtube.com/watch?v=3GJUM6pCpew for an explanation of why. – Arthur Dec 6 '17 at 9:37
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    DVD can actually store progressive (non-interlaced) MPEG2 with just a flag that tells the player to telecine from 24p up to 60i. (This is called "soft telecine"). So a good player can just ignore this flag when and output 24p content, depending on how it's hooked up / configured. But if the DVD was mastered with actual telecined frames fed to the MPEG2 encoder, then it's "hard telecined", and needs to be deinterlaced to display well on a progressive display (like a modern LCD). Hard-telecined DVDs of content that was originally shot on film are very annoying, but of course do exist. – Peter Cordes Dec 6 '17 at 14:11
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    @PeterCordes: There are also (at least) three different ways content can be hard-telecined. Either [1e1o 1e2o, 2e2o 3e3o 4e4o 5e5o], which makes all frames clean, [1e1o, 1e2o, 2e3o, 3e4o, 4e4o, 5e5o], which provies smoothest motion, or [1e1o, 1e2o, 2e2o, 3e3o, 4e4o, 5e5o], which ensures that every film frame appears once cleanly [every sixth frame of video will be a composite]. – supercat Dec 6 '17 at 21:19

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