[ZAGBY]

Ok, I have been reading a few spec sheets on HDTV's here and there and this whole 720p to 1080i "upconvert"to me seems pointless.



Why do I say that well, frist of all the TV reads the horizontal scan rate to display the image, being that is the case it would not be a "upconvert" at all, 720x1280 scans at 45kHz and 1080i scans at 33.75kHz. Also, 720p refreshs at 60fps and 1080i 30fps. Plus, 1080i is only the higher resolution on a static image, on a dynamic image 720p has the higher resolution.




Plus why on earth would you care to re-interlace 720p to 1080i? That's one more stage of processing that does not need to be done. Anyone that knows anything about resolution and displaying a image knows re-interlacing is a bad idea. It would be better just to skip that stage and display 1080i.



What's the point of doing this converting?

 

[jeffmcclan]

Quote:

Originally posted by ZAGBY What's the point of doing this converting?

The point is to display content of a different format than the TV. Some content is broadcast in 720P and other content in 1080i. HDTV television technology either displays 720P native (ie. DLP) or 1080i native.


Converting to the television's display resolution is preferable to viewers only being able to view certain content (based on format). Viewers being able to view only certain broadcasts would not speed up HDTV adoption.

 

[ZAGBY]

I think you mean converting to the displays native resolution no? But even that being the case, a native 720p image must be re-interlaced to 1080i which again is one more stage of processing that will downgrade the image.



In other words because most shows are broadcasted in 1080i they should just go on and make all the channels 1080i. I know ESPN likes 720p because of it's dynamic resolution for fast motion sports but if a set can' t display 720p in it's native format it's going to be converted to 1080i always. The point I am making is that because that must take place with so many TV's it would be better to display the image at native 1080i and not re-interlace 720p to 1080i. The image would look much better that way.

 

[jeffmcclan]

ESPN is not HD yet and thus not in 720P. I believe ABC broadcasts in 720P.

"Sideconverting" from 720P to 1080i must be done in the STB or TV otherwise those owning 1080i televisions would not be able to watch ABC HD. The converse is also true (720P DLP television owners would not be able to view CBS, etc. This is the reason HD STB's have sideconverting capability.


The HDTV specification defines many resolutions in which the stations can broadcast. I don't believe viewers can dictate a selected format to the networks.

 

[ZAGBY]

I am talking about the fact that ESPN has said they will use {in the future} 720p as their native broadcast resolution again because of it's dynamic resolution. Shooting at 720x1280x60.



You can call it whatever you wish to upconvert, sideconvert but a native 720p image must be re-interlaced to be displayed at 1080i. Again, that kind of processing is a bad move.




As long as you have a fixed pixel display that can display 720 vertical pixels by 1280 horizontal pixels it's not a big deal but CRT's have a native sweet spot and the image must be converted to match that sweet spot with broadcast.



Sure if we start to see more 720p broadcast I don't have a problem but, because 1080i has less bandwidth and a higher static spatial resolution and most shows don't have the type of fast jerking motion to drop the dynamic resolution with 1080i, it looks like 1080i is going to win this battle.

 

[John Mason]

Hi Zagby. Very few CRT-based sets can display ABC's 720P. The higher progressive scan rate requires more robust and costly circuit components. So 720p must be sideconverted to 1080i, which HDTV sets can display. -- John

 

[MDRiggs]

You're right that it would be better not to convert 720p to 1080i. The reason manufacturers of CRT-based HD sets normally convert 720p to 1080i is that it reduces the cost of the display (no need to support the 45-kHz horizontal scan rate). It's too bad; 720p input is still better for fixed-pixel displays, however, since it does not have to be deinterlaced.

 

[MDRiggs]

Quote:

Originally posted by ZAGBY As long as you have a fixed pixel display that can display 720 vertical pixels by 1280 horizontal pixels it's not a big deal but CRT's have a native sweet spot and the image must be converted to match that sweet spot with broadcast.

They don't have to be converted to match the "sweet spot"; most CRT-based sets display 480i and 480p signals as 480p and 720p and 1080i signals as 1080i. The optimum beam-spot size for 720p is a lot closer to that for 1080i than the one for 480p is!

 

[ZAGBY]

No, what I was saying is that when one of these CRT based HDTV's has a 720x1280x60 image sent to them they must sideconvert it to 1080i