Converting an interlaced signal to progressive?

[bubble blu]

Ive searched for an answer and cant find one anywhere. I dont understand how you can convert an interlaced signal to a progressive signal if the source wasnt progressive to begin with! Many players, tvs amps etc can upscale to 720p, 1080i and 1080p. If that is the case then why is there a need to broadcast a 1080p signal if a tv or amp can convert it to 1080p? the resolution is the same its just a matter of converting it to progressive? I know what ive said cant be right i just want some anwers!

[kefrank]

In the strictest sense, deinterlacing is just taking the even scan lines from one field and the odd scan lines from the next field and putting them together to form a single, progressive frame.

If the source and destination have the same frame rate and the source was progressive to begin with, this is a pretty simple process. However, complications arise when the source itself was always interlaced (meaning each field comes at a slightly different moment in time) or the resulting frame rate must be different than the source frame rate, requiring a certain cadence of fields matched to frames. With those conditions, you start introducing more complicated processing and usually artifacts. If you really want to know how it all works, just google deinterlacing and read up. The wikipedia page for deinterlacing is a good place to start.

[My_Two_Cents]

Read the following article for some good explanation on the subject.

http://www.hometheaterhifi.com/volum...07-part-1.html

[welwynnick]

Originally Posted by bubble blu

Ive searched for an answer and cant find one anywhere. I dont understand how you can convert an interlaced signal to a progressive signal if the source wasnt progressive to begin with! Many players, tvs amps etc can upscale to 720p, 1080i and 1080p. If that is the case then why is there a need to broadcast a 1080p signal if a tv or amp can convert it to 1080p? the resolution is the same its just a matter of converting it to progressive? I know what ive said cant be right i just want some anwers!

Interlaced video is converted to progressive by de-interlacing. There are different ways of doing this, depending on whether the master was interlaced or progressive.

For films, the original is progressive, and the de-interlacer reverses the telecine process that generated the interlaced video it the first place. This means detecting the telecine cadence and weaving the interlaced fields back together into prgressive frames. This isn't as easy as it sounds, and its never a perfect process.

For TV/video where the original is interlaced, de-interlacing is about interpolation rather than reconstruction. The simplest process is doubling, where each line is simply repeated. This is cheap but gives a poor image. A better way is to treat a 480i field as a 240p frame, and scale it up to 480p. This is more popular, and a bit better than doubling. The best way for now is motion adaptive, where a mixture of doubling and weaving is used, depending on how much motion there is in the picture. Where the picture is relatively static, lines can be woven back together, but where there is significant motion, they are doubled. Depending on the complexity of the de-interlacer, motion adaptation may be detected and implemented on a frame, region or (ideally) pixel-by-pixel basis. There's obviusly a lot of craft and technology in this process, and results vary a great deal.

This is where we are at now, with the best de-interlacers performing both inverse telecine and per-pixel motion-adaptive techniques for both SD and HD video, and many only doing it with SD video. There are lots of reasons why de-interlacing isn't perfect, and while many assume you can perfectly recover 1080p film video from a 1080i broadcast, you can't. If 1080p video for example, could be broadcast instread of 1080i, we would get a better picture. Partly because you avoid the imperfect de-interlacing process, and partly because compression is more efficient with progessive video. Ever wondered why blu-ray looks so much better than DVD?

Nick