[mythtv-users] a little OT: deinterlacing question

[Mark Kendall]

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?

You're forgetting that each interlaced field is from a different point
in time - in PAL terms 1/50th of a second apart (1/60th NTSC). Hence
you can't just put the two fields back together to make the original
frame - you no longer have half the original frame.

The reason it's so difficult is because you have to come up with a
best guess for that missing half - easy in a static scene, almost
impossible in a fast moving one.

Regards

Mark