Deinterlacing 'loses information'

[rogerkip]

I've read here a few times that deinterlacing a video stream results n a loss of information. But that's not strickly correct is it?

There's just as many bits after the deinterlacing, hence the same amount of information? (in the stick defn. of what information is)

I want to take the video I shoot that's interlaced and store as progressive...

BUT, as long as I think I'm degrading the quality I can't stomach it..

There are some VirtualDub/Avisynth filters about that do some fancy stuff - if I can just satisfy myself that quality is not being significantly impaired.

Anyone offer some solace for the 'deinterlace' wannabe?

[pete2828]

when you de-interlace, the encoder will normally remove the other field of the frame and put in its place the frame above it. If what you are trying to do is encode video that is going to played to a TV then encode interlaced. Why you want the mpeg to be progressive?

[adam]

There are two basic ways to deinterlace. You can discard fields, which yes ilterally discards half of your information, or you can combine fields which doesn't necessarily discard any information per se, but it has many other nasty effects. All the other deinterlacing methods are basically derivations or combinations of these two basic methods.

Its a sad simple fact that deinterlacing always has the potential to result in decreased quality or to create specific kind of artifacts. Unless deinterlacing is necessary, for pc playback for example, you should always try to avoid deinterlacing at all costs.

Check out this guide. http://www.100fps.com/

There are descriptions of all the different deinterlacing methods and the pros and cons of each.

[rogerkip]

Check out this guide. http://www.100fps.com/

Good site - have read it & tried converting to 50fps. Excellent result.

But then that doubles the 'information' rate..

I just have in it my mind that because the information rate of both deinterlaced & progressive is the same, then there must be a solution that 'preserves' that information when deinterlacing..

Is there an absolute reason why that is not true?

[lordsmurf]

Your logic is wrong, that's why it is not so.

[rogerkip]

Your logic is wrong, that's why it is not so.

Elaboration?

In terms of sampling theory? - Interlacing samples at twice the rate with half the resolution?

Am I on the right track there?

[presto]

It seems to me that BOB deinterlacing doesn't lose any of the original info. You separate the two fields and play them one after another.

Now there seem to be some practical reasons why this is not the best method to use for most of us.

But if you are asking wether or not an interlaced video can be deinterlaced with no loss of info the answer would be yes. If you have the resources to separate the fields resize them and play them at twice the original speed.

I'm just trying to clarify my own understanding of interlacing by discussing it here. Not delivering a sermon on the mount.

Discuss