How good is HD supposed to be?

[Christopher Woods]

"Upscaling" is a misnomer in this context. That implies a change of picture 
resolution, when there's no resizing going on. What iPlayer does for the 
50p streams is double frame rate deinterlacing, using what looks like a bob 
deinterlace technique.

If you watch content originated in 25i, you will (once the stream steps up 
to 720p50) see the deinterlaced 50p content and you'll notice immediately 
how fluidic motion is - "just like TV", because that's exactly what CRTs 
used to do.

25 interlaced frames per second yields 50 interlaced fields per second (due 
to odd and even line scanning), with the resultant persistence of vision 
effect inducing a pseudo 50 frames per second on viewing as each field's 
worth of capture by the camera sensor 'sees' a slightly different point in 
time. This renders as smoother motion, with a slight loss of sharpness due 
to the low overall temporal resolution, but as it overall appears more 
lifelike the eye prefers it.

25psf (progressive segmented frames) is the "filmic" look, where there's 
only 25 distinct 'captures' of motion per second; the video simply 
'transported' as interlaced. Each field 'sees' its half of the same source 
frame. When decoded properly, you get 100% progressive output. However as 
this gives you half the temporal resolution, motion is visibly less fluid.

Modern flat panels all deinterlace all interlaced source material to 
display a progressive image, but only the higher end panels do quality 
deinterlacing (Yadif or similar) Cheaper screens will usually bob 
deinterlace (computationally less demanding) and porbably convert to 60p as 
their panels and processing will be running internally at 60Hz.

You can even spot some cheap screens doing this as they'll add or duplicate 
frames periodically to equal 60 fps from 50 fps source material, or they'll 
do weird interpolation which can result in jumpy credits or news ticker 
scrolling artifacts.

For an example of 720p50 iPlayer content, watch any episode of EastEnders 
(be sure to enable HD), full screen it and wait for the bandwidth to step 
up to max - you'll need 5 megabits per second minimum to stream (... Or 
just dl it with gip).

For an example of progressive scan material, just about any documentary 
(e.g. Horizon) or episode of Click will do. The latest Horizon about dating 
is 25 PsF: you can see the deinterlacing 'interline twitter' on high 
contrast edges during the programme - an example being the leaves of the 
pot plant moving on the windowsill at around 22 minute mark.


On 29 April 2016 12:44:31 p.m. Dave Lambley <dave at lambley.me.uk> wrote:

> On 29 April 2016 at 00:57, Dave Liquorice <allsorts at howhill.com> wrote:
>> On Thu, 28 Apr 2016 07:07:33 -0500, artisticforge . wrote:
>>
>>
>>>>> NB hvfhd DOES NOT OFFER HIGHER RESOLUTION (CLARITY), only doubled
>>>>> framerate (25FPS x2), which results in smoother scenes where motion is
>>>>> involved!
>>>>
>>>> How does repeating frames improve smoothness of movement? Or does this
>>>> encode upscale each field(*) and encode that to increase the temporal
>>>> resolution?
>>>
>>> It is the frames per second that provide the human eye with the
>>> persistence of vision, the illusion of motion.
>>
>> I could show you 100 fps but if there where only 4 different images
>> displayed the illusion of motion would be no smoother than 25 fps. You only
>> get smoother movement by increasing the number of different images
>> displayed.
>>
>> So if this hvfhd only repeats each frame to get a higher frame there is no
>> increase in smoothness. How ever if they take each field, upscale it and
>> encode as a frame that would inrease the smoothness.
>
> I believe the frame repeating idea is a red herring. Real 50 frame/s
> computer video is a thing which exists. If your browser's up to it you
> can see for yourself here,
> https://www.youtube.com/watch?v=PmNapQdWFKg
>
> You'll need to choose one of the "p50" resolutions on the Quality menu.
>
> Dave
>
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