Wednesday, November 19, 2008

PureCinema film mode

The Pioneer Kuro has a special film mode feature called PureCinema that engages a couple different 24 fps (frames per second) processing algorithms. One of the algorithms helps with film mode de-interlacing, while the other two algorithms produce smoother motion by performing a reverse 3:2 pull-down (inverse telecine) operation and then interpolating the in-between frames or up converting to a 72 Hz frame rate.

The Pioneer Kuro has a native progressive video refresh rate of 60 Hz. Interlaced input sources (480i, 1080i) need to have their even/odd fields reassembled (de-interlaced) first to be progressively displayed. This is called de-interlacing and it removes the teeth artifacts during fast motion and pans.

PureCinema parameters:
  • Off - deactivates PureCinema
  • Standard - only works with 480i and 1080i sources, de-interlaces
  • Smooth - produces smoother moving images by frame interpolation
  • Advance - activates 72 Hz refresh rate for 3:3 pull-down of 24 fps source material for smoother moving images
None of these modes work when the input signal is 1080p60. Speculation as to why is that there's insufficient video processing resources to handle the higher bandwidth of a 1080p60 stream. Standard setting only works with interlaced sources (480i and 1080i). Smooth and Advance settings work with 480i, 480p, 720p, and 1080i input sources.

Standard and Smooth settings display at the standard 60 Hz frame rate. The Advanced setting displays film material at a 72 Hz frame rate. Note that a 72 Hz refresh rate for 3:3 pull-down is automatically engaged whenever a 1080p24 signal is input regardless of mode setting. It doesn't hurt though to play it safe and select Advance mode anyways. Note that 24 * 3 = 72.

Like film in cinema, many prime time TV shows are also recorded at a 24 fps rate, and funnily enough sometimes with a video camcorder. So the Advance mode can be useful for more than just DVD and Blu-ray playback.

What is "dejudder" and how is it related to all of this? Judder is the 3:2 hitching that occurs when 24 fps film material is displayed at a TV's native 60 Hz frame frame. Judder creates a periodic chugging effect that is easiest to see with slow pans or during scrolling credits. Dejudder is the process of removing judder by using video processing. Removing judder, like how the Kuro does with its 72 Hz frame rate is a good thing as it preserves the natural flow of 24 fps film.

Many new LCD flat panels have a 120 Hz refresh rate feature that uses frame interpolation to create smoother motion. Interpolating frames improves the LCD panel's poor motion resolution so LCD manufacturers like this feature because it boosts their specifications. Plasma displays have a superior motion resolution and don't need this technology. Note that with 24 fps film material the LCD's 120 Hz 5:5 pull-down has a similar effect to the Kuro's 72 Hz 3:3 pulldown. Also, the Smooth mode with the Kuro's PureCinema feature does frame interpolation but displays it at 60 Hz.

So dejudder used to mean removing the 3:2 hitching of 24 fps film material by playing it back at a native frame rate multiple of 24. Unfortunately dejudder has morphed into an ambiguous, overused, and abused term that includes both native rate playback and the frame interpolation of all sources (24, 30, and 60 Hz). Some people dislike the frame interpolation feature and disable it. Some LCD HDTV's don't allow 5:5 pull-down of 24 fps film material unless interpolation is enabled and this further complicates the issue. So when you hear the term "dejudder" make sure you understand if it means interpolation, native rate playback, or both.

I keep the PureCinema option set to the Advance mode and it works fine for Blu-ray, DVD, and broadcast HDTV sources. The algorithms are smart enough to prevent odd artifacts most of the time.


ae said...

Some mix-up! Sounds like you are suggesting to leave pure cinema mode in 'Advance' mode always.
Say, source is 480i or 1080i non 24P material, you have 'Advance' selected to get panel fixed @ 72Hz. How do you mathematically co-relate the two with out some sort of pull-up or pull down? This is where you want pure cinema turned 'off' IMO.
Unless you can prove 'Advance' will automatically switch panel to display@60Hz and will pass through the content without any unnecessary re-processing, in such cases.

Erik said...

Yes, I am suggesting keeping the PureCinema Advance mode active all the time for movies and normal TV viewing. Turning it off for video games might be a good idea though.

I think you are confused how 3:2 pull-down and 72 Hz on the Kuro work. Advance mode does not lock the panel at 72 Hz. Instead it activates an algorithm that looks for 24 FPS source material. When 24 FPS is detected it performs a reverse pull-down and sets the refresh rate to 72 Hz. This operation takes less than a second on the Kuro and you can it see happen occasionally but it looks like brief interlace tearing artifacts.

Broadcast movies and many TV shows are recorded at 24P but transmitted at 60 Hz. So the Advance mode can improve normal TV viewing too.

Christian Borchgrevink-Vigeland said...

Hmm, so you say use always use advance for any source (PAL, NTSC, 720p, 1080p, 1080i)? What about source with 23,976 or 25 fps? Thanks

Erik said...

Yes, I always use the PureCinema Advance mode for Blu-ray and broadcast HDTV. I don't watch much DVD or Laser anymore but I use Advance mode for those too. I don't have any PAL sources so I can't comment on 25 fps.

Many prime-time TV shows are shot at 24p so the Advance mode is good for that. The only time I ever see any artifacts is when the source material switches between 24 and 30 fps such as commercial breaks. I've been using PureCinema for the past 9 months and I've been pretty happy with it so far.

Christian Borchgrevink-Vigeland said...

Thanks. Another thing: What exactly is the smooth mode, standard mode, and off?