[mythtv-users] a little OT: deinterlacing question

Steven Adeff adeffs.mythtv at gmail.com
Wed Feb 14 22:27:39 UTC 2007

On 2/14/07, jason maxwell <decepticon at gmail.com> wrote:
> I am just curious. Why is deinterlacing so difficult? From what I've
> read on the topic, an interlaced image is created by breaking a single
> frame into 2 fields of alternating lines. It seems to me that
> reassembling the full frames should be as simple as combining the odd
> and even fields back together. Yet, from what I have read, this will
> always result in some artifacts, most commonly, tearing (mouse teeth).
> Why is this?

couple reasons. one is the interlacing process has more than one
method, so you have to be able to detect which method was used and
proceed from there. things like inverse telecine make this possible,
but some interlaced content doesn't follow this so one of the older
methods needs to be used (brute force basically).

For analog you also have a process looses information in broadcast
which needs to be made up for. When you then digitize this information
you get another loss which needs to be made up for. non-HD
deinterlacing isn't really all that cpu intensive though.

For HD, inverse telecine is the best method, the problem is field
order isn't necessarily followed properly which makes it tough for
inverse telecine processes to work reliably.

> Also, If interlacing was designed to overcome bandwidth limitations of
> the past that no longer plague us, and properly deinterlacing on
> anything but the soon to be extinct CRT monitors is so problematic,
> WTH is 1080i an acceptable standard today?

because early HD displays couldn't handle 1080p but they could handle
1080i. So the thinking was, "we can save a little bandwidth
broadcasting at 1080i instead of 1080p and since noone can actually
watch 1080p yet...". It's similar to why Fox and ABC broadcast in
720p, "we can save a little bandwidth, and since thats all we care
As 1080i TV's are "phased out" 1080i will hopefully go the way of the
do-do(no disrespect meant towards such a fine animal.)

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