On 3 May 2018 21:38:23 RS <richard...@zoho.com> wrote:
On 03/05/18 12:18, Steve Dodd wrote:
Is it possible it depends on the source material? From the BBC quote
earlier it sounds like their "source" material is still mostly HD
interlaced, but perhaps some of their sources are all also
progressive, and those ones get doubled identical frames (which might
be a logical result of feeding 25p material into something that's
designed to interpolate interlaced fields into frames)?
The satellite broadcasts I have seen from the BBC and other broadcasters
are 1920x1080i25 for HD and 720x576i25 or 704x576i25 for SD. Everything
that is broadcast is in an interlaced format at some stage, however it
is generated. Some programmes are only produced for the iPlayer, so
they may be generated in a different way.
A handful of HD is still 1440x1080i25 :( the non-square pixel format is a
great cheat for bandwidth saving. The chroma compression on current
generation terrestrial broadcasting also makes everything look bad. Once
you watch uncompressed HD-SDI you never want anything else :) Some SD is
way below what we would accept as SD resolution as well, all in the name of
cost saving.
Steve is right on the doubled technique, this is the filmic look you see on
documentaries and dramas. That source material will be likely be captured
as progressive frames, then upconverted to 50 fields per second,
'progressive segmented frame' format (PsF) in the edit.
The same image is stored across every two fields that constitute one frame,
meaning you're being shown one effective whole full resolution image, 25
times a second.
With standard interlaced footage, you're being shown overlapping effective
'images' at half-resolution, 50 times a second. Persistence of vision
(well, nowadays, flat panel processing circuitry) bob deinterlaces the
fields to produce 50 images per second.
However, TVs sometimes do this artificially by taking true progressive
sources and interpolating the footage to a higher refresh rate (100/200
Hz). This inherently looks dire and should be disabled.
On some TVs with poorly written image DSP (or badly chosen settings) you'll
see the picture suddenly go 'filmic' as the deinterlace method changes to
blend, which literally blends together pairs of fields to produce 25 frames.
Some explainers of fields, frames and progressive segmented format interlaced:
https://en.m.wikipedia.org/wiki/Progressive_segmented_frame
https://wolfcrow.com/blog/understanding-terminology-progressive-segmented-frames-psf/
https://wolfcrow.com/blog/understanding-terminology-progressive-frames-interlaced-frames-and-the-field-rate/
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