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HDTV film quality confusion

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  • Posted at 11:00am
  • 28 June 2008
  • by DoctorDigital-RT

Q I understand that initial HD transmissions on the new Freesat service will be 1080-interlaced. Is there any hope that this will be upgraded to 1080-progressive in the near future, with a 24-frames-per-second option for films? I have a 1080p HDTV and want to maximise the quality of picture received.
Peter Cash, Manchester

A It's no to both, we're afraid. The highest-quality HD system at the moment, called 1080p, is used by Blu-Ray (high-definition DVD ), but not much else: no UK HD broadcaster transmits in this format as yet. Most are broadcasting in 720p, which is lower quality, although many argue it works better for sport.

The "p" is important: it stands for "progressive" and means each frame of the TV picture is displayed in one go. There's also 1080i, which offers the same resolution (1080 lines on the screen, as opposed to 720), but the picture is interlaced: half of the frame appears first on even-numbered lines, then the rest of it follows an instant later, on the odd-numbered lines. It's so fast you don't see it, but there's still a big difference when you compare 1080p with 1080i. (Standard-definition TV is 480i.) HD programme-makers choose which format to use: Sky and Freesat support both 720p and 1080i.

As for films, Freesat's spokesperson tells us: "In common with all TV platforms in Europe, Freesat broadcasters replay films shot at 24fps at the higher speed of 25fps."

**

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