2 replies to this topic

[pheggie]

Ultra-HD may require faster framerates than 120fps says BBC
http://www.3dfocus.c...hnologist/13286

[pgdownload]

Interesting how increasing resolution leads to a reduction in image quality.

Regards

Peter Gillespie

[MLXXX]

pgdownload, on 23 May 2013 - 09:26 AM, said:

Interesting how increasing resolution leads to a reduction in image quality.

A higher resolution format does require a higher bitrate after compression with a video codec to obtain the benefit/visibility of higher resolution. If you use a DVD bitrate when encoding a Full HD source you cannot expect a good quality transfer.

A higher resolution format can reveal flaws otherwise hidden.

The flaw the article focusses on is insufficiency of frame rate. 24fps is a terribly slow frame rate. It introduces motion blur with even a very slow plan. It necessitates a very long exposure time to avoid a stroboscopic look when the film is displayed. Frame interpolation can assist if the pan is steady and the picture content stable.

It is instructive to consider how many pixels are omitted through use of a slow frame rate. Assume a video camera using a stationary tripod, and that the camera is turned so as to do a horizontal pan that takes 5 seconds for an object to pass from the right edge of the picture to the left edge. At 24fps, in 5 seconds there will be 120 frames. If the format is Full HD, there are 1920 pixels horizontally. During the pan, the number of pixel positions moved per frame is 1920/120 =  16. If the shutter is set for 1/48th sec (the conventional shutter angle of 180 degrees), then each frame will consist horizontally of 240 sets of the summed blur of 8 horizontal pixels. There will then be a gap of 8 horizontal pixel positions while the shutter is shut. If there is random movement in that time, it is lost. Then there will the capture of another 240 sets of the summed blur of 8 horizontal pixels.

If you connect a Full HD video camera operating at 24fps via HDMI to a display such that there is no lossy video compression codec intervening, you will see how horribly the horizontal resolution deteriorates as you do a slow pan of the surroundings.

There is a very significant improvement if using 50i, 60i, 50p, or 60p during a slow pan.

Using a 4K video camera and a 4K screen will not improve the visible resolution during a slow pan unless there is sophisticated frame interpolation and little or no movement in what is being shot. And... if you increase the resolution and increase the frame rate, you can expect more video noise.   ** SIGH **

24fps by providing a longer exposure time can give reduced video noise (or reduced visibility of distracting film grain). Provided the motion is sedate and pans done sparingly and carefully this low frame rate established in the 1920s can limp along fairly well when applied to the 1920x1080 Blu-ray format for 2D.

The other day I was watching Life of Pi. Early in the movie, Pi, then a young boy, enters a church. The camera pans to show the interior of the church. At that point there is a disturbing interference to the 3D viewing effect for my eyes. The jitter, which is a slight nuisance for 2D, leads to a breakdown in the brain's opportunity to process detailed parallax differences, in order to perceive the stereoscopic 3D effect.

I found the 48fps, used in The Hobbit, a distinct improvement for viewing in 3D.

Edited by MLXXX, Yesterday, 08:59 AM.