[MEncoder-users] compression: 1080i versus 720p

[RC]

On Mon, 21 Dec 2009 04:25:24 -0600
Andrew Berg <bahamutzero8825 at gmail.com> wrote:

> Right, but 60 half-height fields contain the same amount of data as 30
> full height frames, do they not? 

While they are interlaced, yes.  Afterwords, no.

With interlaced video, you can turn 30i frames into 60p frames.  After
deinterlacing, you cannot, as motion has been irreversibly damaged by
merging two fields, thereby halving the frame-rate.

> Deinterlacing does not reduce the amount of data. 

Yes, it does.  Deinterlacing, for the most part, involves
deciding when there is motion, and how much of the current frame has to
be discarded and replaced with interpolated data from the alternate
field.

The problem here is that you're thinking of "data" as simply raw,
uncompressed pixel counts.  In fact it's much easier to compress one
large image than it is two images that are each half the size.



-- 
Ha. I'm the idiot.