Motion interpolation

Motion interpolation or motion-compensated frame interpolation (MCFI) is a form of video processing in which intermediate animation frames are generated between existing ones by means of interpolation, in an attempt to make animation more fluid and to compensate for display motion blur.

Hardware applications

Displays

Motion interpolation is a common, optional feature of various modern display devices such as HDTVs and video players, aimed at increasing perceived framerate and/or alleviating display motion blur, a common problem on LCD flat-panel displays.

Difference from display framerate

A display's framerate is not always equivalent to that of the content being displayed. In other words, a display capable of and/or operating at a high framerate does not necessarily mean that it can or must perform motion interpolation (most TVs ship with any such feature enabled by default). For example, a TV running at 120 Hz and displaying 24 FPS content will simply display each content frame for five of the 120 display frames per second. This has no effect on the picture other than eliminating the need for 3:2 pulldown and thus film judder as a matter of course (since 120 is evenly divisible by 24). Eliminating judder results in motion that is less "jumpy" and which matches that of a theater projector. Motion interpolation can be used to reduce judder, but it is not required in order to do so.[1]

Relationship to advertised display framerate

The advertised framerate of a specific display may refer to either the maximum number of content frames which may be displayed per second, or the number of times the display is refreshed in some way, irrespective of content. In the latter case, the actual presence or strength of any motion interpolation option may vary. In addition, the ability of a display to show content at a specific framerate does not mean that display is capable of accepting content running at that rate; most consumer displays above 60 Hz do not accept a higher frequency signal, but rather use the extra frame capability to eliminate judder, reduce ghosting, or create interpolated frames.

As an example, a TV may be advertised as "240 Hz", which would mean one of two things:

  1. The TV can natively display 240 frames per second, and perform advanced motion interpolation which inserts between 2 and 8 new frames between existing ones (for content running at 60 FPS to 24 FPS, respectively). For active 3D, this framerate would be halved.
  2. The TV is natively only capable of displaying 120 frames per second, and basic motion interpolation which inserts between 1 and 4 new frames between existing ones. Typically the only difference from a "120 Hz" TV in this case is the addition of a strobing backlight, which flickers on and off at 240 Hz, once after every 120 Hz frame. The intent of a strobing backlight is to increase the apparent response rate and thus reduce ghosting, which results in smoother motion overall. However, this technique has nothing to do with actual framerate. For active 3D, this framerate is halved, and no motion interpolation or pulldown functionality is typically provided. 600 Hz is an oft-advertised figure for plasma TVs, and while technically correct, it only refers to an inter-frame response time of 1.6 milliseconds. This can significantly reduce ghosting and thus improve motion quality, but is unrelated to interpolation and content framerate. There are no consumer films shot at 600 frames per second, nor any TV processors capable of generating 576 interpolated frames per second.

HDTV implementations

The commercial name given to HDTV motion interpolation technology varies across manufacturers, as does its implementation.

Software applications

Video playback software

Motion interpolation features are included with several video player applications.

Video editing software

Some video editing software and plugins offer motion interpolation effects to enhance digitally-slowed video. Adobe After Effects has this in a feature called "Pixel Motion". The effects plugin "Twixtor" is available for most major video editing suites, and offers similar functionality.

Virtual reality

On October 6, 2016, Oculus VR announced that it would enable the use of motion interpolation on the Oculus Rift virtual reality headset, allowing it to be used on computers whose specifications are not high enough to render to the headset at 90 frames per second.[19][20]

Side effects

Visual artifacts

Motion interpolation on certain brands of TVs is sometimes accompanied by visual anomalies in the picture, described by CNET's David Carnoy as a 'little tear or glitch' in the picture, appearing for a fraction of a second. He adds the effect is most noticeable when the technology suddenly kicks in during a fast camera pan.[1] Television and display manufacturers refer to this phenomenon as a type of digital artifact. Due to the improvement of associated technology over time, such artifacts appear less frequently with modern consumer TVs, though they have yet to be eliminated entirely.

Soap opera effect

As a byproduct of the perceived increase in framerate, motion interpolation may introduce a "video" (versus "film") look. This look is commonly referred to as the "soap opera effect", in reference to the distinctive appearance of most broadcast television soap operas, which were typically shot using less expensive 60i video rather than film.[21] Many complain that the soap opera effect ruins the theatrical look of cinematic works, by making it appear as if the viewer is either on set or watching a behind the scenes featurette.[22] For this reason, almost all manufacturers have built in an option to turn the feature off and/or lower the effect strength.

Others appreciate motion interpolation as it reduces motion blur produced by camera pans and shaky cameras and thus yields better clarity of such images. It may also be used to increase the apparent framerate of video game software for a more realistic feel, though the addition of input lag may be an undesired side effect.[23] This "video look" is created deliberately by the VidFIRE technique to restore archive television programs that only survive as film telerecordings.[24] The main differences between an artificially and naturally high framerate (via interpolation versus in-camera), are that the latter is not subject to any of the aforementioned artifacts, contains more accurate (or "true to life") image data, and requires more storage space and bandwidth since frames are not produced in realtime.

See also

References

  1. 1 2 Carnoy, David (October 25, 2007). "Six things you need to know about 120 Hz LCD TVs". CNET.com. Retrieved 2008-02-02.
  2. ↑ "Archived copy". Archived from the original on January 8, 2008. Retrieved 2008-02-01.
  3. ↑ "Archived copy". Archived from the original on September 11, 2010. Retrieved 2010-09-16.
  4. ↑ "Archived copy". Archived from the original on March 30, 2014. Retrieved 2013-01-06.
  5. ↑ "Archived copy". Archived from the original on January 20, 2008. Retrieved 2008-02-01.
  6. ↑ "Archived copy". Archived from the original on March 14, 2010. Retrieved 2010-03-22.
  7. ↑ "Sharp intros slate of new AQUOS LCD HDTVs, first LED models included". Engadget.com. Retrieved 2016-11-30.
  8. ↑ "Sharp debuts 60-inch 240Hz Aquos LED LCD TV, 68-inch set with a touch of yellow in its RGB". Engadget.com. Retrieved 2016-11-30.
  9. ↑ "Press Articles – Sony". News.sel.sony.com. Retrieved 2016-11-30.
  10. ↑ "ACK.de - Professionelle Domain Dienstleistungen und Beratung". Motionflow.eu. Retrieved 2016-11-30.
  11. ↑ "Archived copy". Archived from the original on December 31, 2012. Retrieved 2012-12-20.
  12. ↑ "Black Friday Deals & Savings on Top Corel Products". Corel.com. Retrieved 2016-11-30.
  13. ↑ "Crystal TV for PC, Mac, Windows Phone, Symbian, Android, iPad, iPhone and iPod Touch!". Crystal Reality. 2003-08-18. Retrieved 2016-11-30.
  14. ↑ "Video Enhancement – TrueTheater Technology". CyberLink. Retrieved 2009-08-24.
  15. ↑ "Picture2". Mirillis.com. 2010-07-01. Retrieved 2016-11-30.
  16. ↑ "madVR". madVR. Retrieved 2016-11-30.
  17. ↑ "Home". DmitriRender.ru. Retrieved 2016-11-30.
  18. ↑ "Bluesky Frame Rate Converter". Bluesky23.yukishigure.com. Retrieved 2016-11-30.
  19. ↑ "Oculus lowers minimum Rift specs using "asynchronous spacewarp" tech". Ars Technica. Retrieved 6 October 2016.
  20. ↑ "Oculus Rift has a new minimum spec, $499 entry-level PC". Polygon. Retrieved 6 October 2016.
  21. ↑ Biggs, John (August 12, 2009). "Help Key: Why 120 Hz looks "weird"". crunchgear.com. Retrieved 2009-11-13.
  22. ↑ Moskovciak, Matthew (January 8, 2008). "Vizio adds 120 Hz LCDs to its lineup". CNET.com. Retrieved 2008-02-01.
  23. ↑ "What is the Soap Opera Effect?". Techtarget.com. Retrieved 2011-04-20.
  24. ↑ "VIDFIRE – The Doctor Who Restoration Team". restoration-team.co.uk/. Retrieved 2011-05-19.
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