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HDTV blur

HDTV blur is a common term used to describe a number of different artifacts on consumer modern high definition television sets:

The following factors are generally the primary or secondary causes of HDTV blur; in some cases more than one of these factors may be in play at the studio or receiver end of the transmission chain.

  • Pixel response time on LCD displays (blur in the color response of the active pixel)
  • Slower camera shutter speeds common in Hollywood production films (blur in the HDV content of the film)
  • Blur from eye tracking fast moving objects on sample-and-hold LCD, Plasma, or Microdisplay. [1]
  • Resolution resampling (blur due to resizing image to fit the native resolution of the HDTV)
  • Blur due to 3:2 pulldown and/or motion-speed irregularities in framerate conversions from film to video
  • Computer generated motion blur introduced by video games [2]

Contents

Causes

It is common for observers to confuse or misunderstand the source of blurring on HDTV sets. There are so many different possible causes, many of them being possible simultaneously.

Pixel response times need to be below 16.67 milliseconds in order to fully represent the bandwidth of color changes necessary for 60 Hz video. But achieving faster than 16.67 does not eliminate motion blur because of the least understood of all of these blur effects is that due to eye tracking.

LCDs often have a greater motion blur effect because the pixel in an LCD remains lit unlike the CRT phosphors that merely strobe for a very brief period of time. Reducing the time an LCD is lit has been shown to reduce motion blur due to eye tracking by decreasing the time period the backlit pixels are on.[3] However, an instant strobe is required to completely eliminate the retinal blurring. [4] [5] [6]

Fixes

Strobing Backlight

  • Philips created Aptura also known as ClearLCD to strobe the backlight in order to reduce the sample time and thus the retinal blurring due to sample-and-hold. [7][8]
  • Samsung developed "LED Motion Plus" strobed backlighting and is available on the "Samsung 81 Series" LCD screens as of August 2007.[9]
  • BenQ developed SPD (Simulated Pulse Drive) also more commonly known as "black frame insertion" and they claim that their images are as stable and clear as CRT's.[10] [11] This is conceptually similar to a strobing backlight.

100 Hz +

Some displays cut the amount of blur while adding to the latency by inserting in-between frames. For instance some LCD TVs supplement the standard 50/60 Hz signal by interpolating an extra frame between every pair of frames in the signal so the display runs at 100 Hz or 120 Hz depending on which country you live in. PAL/SECAM countries adopt 100 Hz and NTSC countries typically adopt 120 Hz. [12] It's notable that this solution is adequate for movies (which must have blur to begin with to solve double imaging problems with higher shutter speeds on film) but not for video games, which require less than 1 frame or 16.66 ms of latency for optimal playability.[citation needed] [13]

One possible advantage of a 100 Hz + display is superior conversion of the standard 24frame/s film speed. Usually movies and other film sources in NTSC are converted for home viewing using what is called 3:2 pulldown which uses 4 frames from the original to create 5 (interlaced) frames in the output. As a result 3:2 pulldown shows odd frames for 49.98 milliseconds and even frames for 33.33 milliseconds. At 120Hz 5:5 pulldown from 24frame/s video is possible[14] meaning all frames are on screen for the same 41.65 milliseconds. This eliminates the jerky effect associated with 3:2 pulldown called telecine judder. However, to use 5:5 pulldown instead of the normal 3:2 pulldown requires either support for 24 frame/s output like 1080p/24 from the DVD/HD DVD/Blu-ray Disc player or the use of reverse telecine to remove the standard 3:2 pulldown. At the moment few TVs support 5:5 pulldown [15]. However, some TVs do 3:3 pulldown at 72 Hz or 4:4 at 96 Hz.[16] While several TVs offer 120 Hz and claim to eliminate judder (eg. Sony's MotionFlow), almost none of them use 5:5 pulldown except for a few Japanese Toshiba sets[17][18]. PAL countries speed the 24 fps film speed by 4% to obtain 25 fps, therefore movies in the PAL format are completely free of Telecine judder effects. As a result, 100 HZ televisions do not suffer from telecine judder as 120 Hz models do.

  • Sony calls their 100 Hz + technology "Motionflow".[19]
  • JVC calls their 100 Hz + technology "Clear Motion Drive". [20]
  • Toshiba calls their 100 Hz + technology "Clear Frame". [21]
  • Samsung calls their 100 Hz + technology "Auto Motion Plus". [22]

What they are all doing is the equivalent of "in-betweening" in animation, where the key frames are drawn by the source video and the computer interpolates the frames in between the key frames. If video frame 1 has a man with his hand at waist level and video frame 2 has the same man with his hand a little bit above waist level, then the video processor interpolates a frame between them with the man having his hand half way between the two positions, just as the frame sequence would have looked if it had been captured at 100 + frames-per-second rather than 50/60 fields-per-second. The catch is, the original video frames are still blurred compared to what a true 100 + Fps rate would look like. The in between frames are also synthetic, so there is no guarantee they would actually match what you would have seen at a true 100 Hz + Fps. Basically, all this depends on how good the computer algorithms are at synthetic generation of frames. Despite these issues, the above techniques make a huge visible difference to blur and picture motion, a difference that can easily be noticed by anyone with such a television.

Laser TV

Laser TV is reported to eliminate double imaging and motion artifacts by strobing the image similar to the way that a CRT works. [23] Laser TV is generally not yet available, and the results are not confirmed to solve the problem, but claims have been made on television broadcasts such as KRON 4 News' Coverage of Laser TV from October 2006. [24]

See also

External links

References

  1. ^ Charles Poynton is an authority on artifacts related to HDTV, and discusses motion artifacts succinctly and specifically
  2. ^ Computer Game Engine that makes use of Motion Blur Effects
  3. ^ Publishing from February 2006 from Sharp discussing LED flashing to reduce temporal retinal blur effects with decreasing on-time duty cycle for the backlight.
  4. ^ How human eyes sense the motion blur on moving object of LCD panel?
  5. ^ Three methods of classic MPRT measurement equipments.
  6. ^ Another PDF describing MPRT
  7. ^ Philips brochure advertising Aptura backlighting that reduces retinal blurring significantly
  8. ^ Review of a philips Aptura set that discusses Aptura briefly
  9. ^ User manual for Samsung 81 Series TVs with LED Motion Plus technology
  10. ^ BenQ described "black frame insertion" on FP241VW monitor release in 2006
  11. ^ BenQ describes "Simulated Pulse Drive" which seems to be the same technology but renamed for their newer monitor line announced December 2007
  12. ^ JVC Makes first 120 Hz set to cut retinal blur in half
  13. ^ Resolving latency issues in HDTV video games
  14. ^ Patent for 5:5 pulldown
  15. ^ Gearwork Article on 1080p/24
  16. ^ Sets that support 3:3 pulldown at 72 Hz or 4:4 at 96 Hz
  17. ^ Toshiba set that supports 5:5 pulldown
  18. ^ Toshiba Introduces All Encompassing 2008 LCD TV Line with a Series for Every Lifestyle
  19. ^ [1]
  20. ^ [2]
  21. ^ [3]
  22. ^ [4]
  23. ^ Evans and Southerland use column scanning laser to eliminate motion blur on their high end laser projection system
  24. ^ KRON 4 News in Bay Area covers coherent and novalux joint venture laser television project


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Categories: High-definition television | Television technologyHidden categories: All articles with unsourced statements | Articles with unsourced statements since August 2007

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