[mythtv-users] High end, state of the art Myth Frontend

[Jeff Siddall]

On 09/18/2013 04:17 PM, Joseph Fry wrote:
> On Wed, Sep 18, 2013 at 4:07 PM, Jeff Siddall <news at siddall.name> wrote:
>> On 09/18/2013 03:42 PM, Eric Sharkey wrote:
>>>
>>> On Wed, Sep 18, 2013 at 3:36 PM, Jeff Siddall <news at siddall.name> wrote:
>>>>
>>>> But at a given bitrate I am becoming more convinced that interlacing is a
>>>> good tradeoff.  The loss of resolution with 720 is irreversible whereas
>>>> deinterlacing done well can result in a very watchable, and potentially
>>>> much
>>>> sharper, image.
>>>
>>>
>>> You can scale up an image from 720 to 1080.  The result is no less
>>> fake than what you get by deinterlacing.  Going from 1080p to 1080i or
>>> 720p both represent irreversible information loss.
>>
>>
>> Yes, I agree, you can scale an image up (and that is ultimately what happens
>> when a 720p is shown full screen on a native 1080 display).
>>
>> However, I disagree that 1080i represents irreversible information loss.
>> With 1080i60 you get two subsequent 540 line images that, when combined,
>> result in a full resolution 1080 line image.  If there is no motion in the
>> image then no information is lost.
>
> But that's not what happens.
>
> They may use a 1080p/60 camera to shoot the footage, but then they
> take half the fields of each frame and create 1080i/60 from it.
> Effectively losing 1/2 of each frame.

Well, yes, but (and this is a big but) they don't lose the same half in 
two subsequent fields.  One contains even and one contains odd lines. 
So if your content isn't moving then after two frames you have all 1080 
lines -- something you simply can't get in 720p.

> What your suggesting is that they are creating 1080p/30 but only
> transmitting half the image at a time... which would be pointless...
> they could transmit 1080p/30 in the same bandwidth at 1080i/60... no
> need to interlace it.

Yes, theoretically they could make 1080p30 but in reality deinterlacing 
gives 60 frames per second with half the lines in each frame being 
interpolated.  This is why the quality of the deinterlacer has such a 
large impact on the final video.

See here for more info:

http://en.wikipedia.org/wiki/Interlacing

Also, I incorrectly stated they switched to 720p30 when they actually 
switched to 720p60.

Bottom line is that the 1080i picture is significantly sharper, 
especially for low motion content, but the tradeoff is it can suffer 
some from motion artifacts related to deinterlacing.

Jeff