[Spike Spiegel]

If i'm watching a program that's being broad-casted in 720p on a 1080i TV, what will the resolution be on my screen?Would it be 720p,720i,or something else?

 

[psblake]

will "upconvert" the 720p signal to 1080i.

 

[bfdtv]

The "effective" resolution of the 720p program will be somewhere between 1280x540p and 1280x720i, depending on the scaler in your box/TV. You'll also lose the 60 fps of the ABC/FOX/ESPN broadcasts -- you'll get 30 fps instead.

 

[trbarry]

Quote:

You'll also lose the 60 fps of the ABC/FOX/ESPN broadcasts -- you'll get 30 fps instead.

If this is true it is only thru a trick of semantics since both 1080i and 1280p have 60 pictures / second. In 1080i those pictures are called fields instead of frames and each represent only half of a complete picture, but there are still 60 of them with each containing as many active pixels as a full 720p frame.


We probably also have to consider an "effective" frame rate but I can't off hand give a good definition of the term. But you could probabably say that some "effective frame rate" is also lost in the conversion process.


- Tom

 

[John Mason]

Effective resolution always seems too vague IMO, so I prefer using "resolvable detail", as outlined earlier . During mid-90s ATSC approval testing (based on table 2.3 ), using the best gear then available, 720p delivered 1139X550 resolvable detail for static B&W test-pattern images and 1068X420 for moving (5-rpm) B&W test patterns. In both cases the format resolution remained fixed at 1280 horizontal samples/lines/pixels for each of the 720 horizontal scan (or row) lines. Since test patterns require less compression than moving images it's likely, IMO, that actual motion video has even less resolvable detail since MPEG-2 discards high-frequency detail to achieve compression. ATSC compressed video (OTA) is typically less than ~17 million bits per second (Mbps) compared to about 1,000 Mbps uncompressed for the original samples.


When sideconverted from 720p to 1080i, the resolvable detail can't increase over that captured originally. That is, even though the format resolution has shifted to 1920X1080i, as the resolvable detail varies depending on motion within each image frame, the additional electronically generated pixels won't supply more actual picture details. Nevertheless, sideconverted images might appear 'sharper', just as putting more pixels on your computer screen by boosting format resolution makes images seem sharper. This recent article outlines the role of sharpness in HD viewing.


Sometimes sideconverted 720p-to-1080i appears more colorful on my 64" 1080i CRT RPTV screen. Just speculation, but that might be because three of four ATSC approval tests (link above) showed that 720p delivered more color resolution than 1080i, even though the latter format has about double the spatial format resolution. It seems reasonable that this enhanced color detail would be carried into the 1080i format during sideconversion. -- John

 

[Joxer]

Depends on your model HDTV. Some models like Panasonic's don't support 720p input at all - you would get a black screen on such a set.

 

[Jordan420]

Quote:

Originally posted by Joxer Depends on your model HDTV. Some models like Panasonic's don't support 720p input at all - you would get a black screen on such a set.

Joxer does not mean that some TV's would never be able to watch a station broadcasting in 720p. The signal has to be scaled to a resolution the TV can accept.


My tv has a built in tuner, & will not accept a 720p input thru the component inputs but has no problem displaying ABC & FOX OTA, and also has no problem displaying espn-hd from sat. which outputs 1080i.


Just because a tv will not accept a 720p input does NOT mean that channels broadcast in 720p will display a black screen when trying to view them thru either an internal or external tuner outputing 1080i.


Every ATSC tuner is capable or receiving all 18 digital broadcast standards and outputting them in a way that is viewable on any HDTV ready set


I just don't want some one to freak out & think that if they buy the wrong display they won't be able to view 2 of the major networks.


My display is from 2001 and my next TV will accept all formats to 1080p