[HN Gopher] Interlacing, Deinterlacing, and Everything in Between
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Interlacing, Deinterlacing, and Everything in Between
Author : MindGods
Score : 44 points
Date : 2021-05-16 05:56 UTC (1 days ago)
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| msla wrote:
| > We hit a strange truth about analog monochrome television: the
| vertical resolution is strictly limited: it's the number of lines
| you draw. But the horizontal resolution, the resolution within
| each line, is basically infinite; it's a purely analog signal.
| The only thing that holds it back is how quickly the electronics
| in your television can keep up.
|
| No, it's strictly limited by the bandwidth of the television
| signal. You could have infinitely responsive circuitry but you'd
| still have horizontal resolution limited by the bandwidth of the
| video portion of the broadcast TV signal.
|
| About all you can say is that analog TV does not have pixels.
|
| Anyway, here's a video (part of a series) on how analog TV works:
|
| https://www.youtube.com/watch?v=l4UgZBs7ZGo
|
| Full playlist:
|
| https://www.youtube.com/playlist?list=PLv0jwu7G_DFUGEfwEl0uW...
| whatshisface wrote:
| > _About all you can say is that analog TV does not have
| pixels._
|
| Color analog TVs have discrete patches of different phosphors.
| TazeTSchnitzel wrote:
| Those aren't really pixels though: the signal can (and does)
| vary within them.
| Hackbraten wrote:
| > Capacitors were still called condensers.
|
| Funny that in German, a capacitor is still a _Kondensator_ to
| this day.
| trotFunky wrote:
| The French word has kept the root too : "condensateur" !
| jayd16 wrote:
| Great pun in the title.
| chrisseaton wrote:
| What does industry do about interlacing?
|
| I understand many TV shows were recorded and mastered on video
| with interlacing. When they re-release the TV shows for example
| for Netflix - what are they currently doing?
| jlarcombe wrote:
| Dont know about Netflix but I believe the BBC archive uses
| Martin Weston's adaptive 3-field deinterlacer. I think it's out
| of patent now and is available in ffmpeg and similar...
| aardvark179 wrote:
| The BBC has an easier job than NTSC based outfits because
| filmed material will have been captured at 25 frames per
| second and converted to 50 fields per second. They are less
| likely to have problems like 3:2 interlacing breaking in an
| edit which used to be quite common in NTSC.
| cogman10 wrote:
| Last I heard, netflix has studios send them progressive video
| and lets them deal with de-interlacing.
|
| AFAIK, for enthusiasts, the best deinterlacer is "QTGMC"
| http://avisynth.nl/index.php/QTGMC
|
| For stuff shot like post 2015, I don't think anyone is
| interlacing anymore. Everything is progressive.
|
| https://netflixtechblog.com/high-quality-video-encoding-at-s...
| ubercow13 wrote:
| TV broadcasts are often still interlaced in some places
| toast0 wrote:
| Ideally, they deliver it to Netflix in the original form,
| properly marked as interlaced (or not) or for the small handful
| of shows filmed in 24p, as original films, marked as such
| (rather than presented with a 3:2 pulldown as originally
| broadcast).
|
| In practice (based on experience as a viewer), things are kind
| of messy, and sometimes the markings must be off, or someone
| did a really poor deinterlace, and there's visible combing all
| over, ugh.
|
| Netflix, or my streaming player, or my display can all
| deinterlace, so there's no need for the source to do it.
| cogman10 wrote:
| From what I've read, Netflix has been investing quite a bit
| towards automatically detecting these sorts of issues and
| rejecting video that's been poorly handled by the studios.
| AFAIK, they reject interlaced content.
|
| From a compression standpoint, netflix wants everything to be
| progressive. Interlaced media (funnily) requires a lot more
| bandwidth to transmit with modern codecs. I say funnily
| because interlacing was a technique to save bandwidth for
| analog transmissions. It gives the illusion of a higher
| framerate. Unfortunately, modern video codecs work by
| tracking object movement from one frame to the next.
| Interlacing really messes that up requiring more bits spent
| for the same amount of quality.
|
| Some of the older codecs have interlacing built into the
| standard (mpeg2 and h264). Newer ones have banned it all
| together (VP9, AV1) due to the codec complexity it introduces
| for very little benefit.
|
| https://netflixtechblog.com/high-quality-video-encoding-
| at-s...
| stormbrew wrote:
| > It gives the illusion of a higher framerate.
|
| I mean, it doesn't really give the illusion of it. It _is_
| higher frame rate when recorded from a camera[1], as most
| TV was. The fields are independent moments in time (and you
| can very clearly see this in freeze-frames of interlaced
| motion, that 's part of what combing is).
|
| What it gives the illusion of is greater vertical
| resolution.
|
| [1] video game systems that used interlacing, like the n64,
| playstation, and up until the hdmi era, did not usually do
| this afaik, opting to instead drop the frame rate to 30fps
| with 2 fields per frame, so they really were in many ways
| the worst of all worlds.
| TazeTSchnitzel wrote:
| > up until the HDMI era
|
| I think that's wrong: didn't PS2-era consoles use
| interlacing to get higher resolution? You're definitely
| right for PS1 and earlier though.
| AnIdiotOnTheNet wrote:
| I think what parent is saying is that camera-captured
| interlaced video was displaying scanlines from
| _different_ images in each field, whereas game consoles
| using interlacing displayed the even /odd lines of the
| _same_ image in two fields.
|
| Thus parent's argument is that we can consider camera-
| captured interlaced video to be 60 (or 50 for PAL) fps
| despite being interlaced, but games using interlacing
| were 30 fps. It makes sense to me.
| monocasa wrote:
| It was a choice of the game. There were definitely truly
| 60FPS interlaced games during the PS2 generation.
| NathanielK wrote:
| > video game systems that used interlacing, like the n64,
| playstation, and up until the hdmi era, did not usually
| do this afaik, opting to instead drop the frame rate to
| 30fps with 2 fields per frame, so they really were in
| many ways the worst of all worlds.
|
| 480i Nintendo consoles (N64, GCN, WII) all had many 60FPS
| games. The 30FPS limit was almost always because of the
| relatively underpowered hardware. Some N64 games even ran
| at 20FPS!
| spookthesunset wrote:
| Technology Connections has a good video on how CRT's work:
| https://youtu.be/l4UgZBs7ZGo
| Rendello wrote:
| Captain Disillusion has a good video on interlacing
| specifically:
|
| https://www.youtube.com/watch?v=5eu_KjKsnpM
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