Topic: This thing we call "1080i"

[comitatus]

hello, sorry for such a newbie questions but i was playing with my t.v (a panny pv70) and i noticed that it can do 1080i. my hubby tells me to stick with the t.v's native res which is 720p, but would switching to 1080i have some sort of improvement? or since it's not native res, will it look worse? i would like to have some feed back on users who use 1080i as a resolution for a 720p t.v in the area of dvd or blu-ray. also, since we would be having the skycable hd broadcast and that offers a max of 1080i will that be better than 720p?

thank you

[gearhead000]

if the tv's native res is 720p, better stick with it. but if the incoming signal from sky is 1080i, you can test which has better scaler, the tv or the tv box/set top box (if it has the capability to change output resolution).

[Clondalkin]

From WIKI

Some broadcasters use 720p50/60 as their primary high-definition format; others use the 1080i standard. While 720p presents a complete 720-line frame to the viewer between 24 and 60 times each second (depending on the format), 1080i presents the picture as 50 or 60 partial 540-line "fields" per second (24 complete 1080-line fields, or "1080p24" is included in the ATSC standard though) which the human eye or a deinterlacer built into the display device must visually and temporally combine to build a 1080-line picture.

To get all 1080 interlaced lines to appear on the screen at the same time on a progressive high-definition display, the processor within the HD set deinterlaces incoming video by either weaving together two 540-line fields, or by doubling lines in each field, effectively converting fields to frames. The first deinterlacing method is used for static scenes, the second one is used for scenes with motion. Cheaper TVs always use line doubling, while more expensive TVs use complex algorithms to analyze motion between two fields. Because of the deinterlacing, 1080i video with static scenes has more vertical resolution than 720p video, while the resolution in moving scenes is lower because of field doubling.

While 1080i has more scan lines than 720p, they do not translate directly into greater vertical resolution. Interlaced video is usually blurred vertically (filtered) to prevent twitter. Twitter is a flickering of fine horizontal lines in a scene, lines that are so fine that they only occur on a single scan line. Because only half the scan lines are drawn per field, fine horizontal lines may be missing entirely from one of the fields, causing them to flicker. Images are blurred vertically to ensure that no detail is only one scan line in height. Therefore, 1080i material does not deliver 1080 scan lines of vertical resolution. However 1080i provides a 1920-pixel horizontal resolution, greater than 720p's 1280 resolution.

The data rate is also a concern in broadcasting. 1080i has a raw rate of 51.84 million pixels per second at 50Hz, and 62.208 at 60Hz. 720p50 has a rate of 46.08Mpx/s, while 720p60 is 55.296, and the p25 and p30 modes are exactly half, respectively. (For comparison, 480i and 576i modes average around 10Mpx/s.) Transmission of greater total pixel rates from all virtual channels multiplexed on a physical TV channel (whether a TV station or on digital cable) requires greater video data compression. Excessive lossy compression can look much worse than a lower resolution with less compression, which in turn affects the choice of 720p or 1080i, and low or high frame rate.

In the USA, 720p60 is used by ABC, Fox Broadcasting Company and ESPN because the smoother image is desirable for fast-action sports telecasts, where as 1080i is used by CBS, NBC, HBO, Showtime and Discovery HD due to the crisper picture, particularly in non-moving shots. Ion appears to use 720p30 over the air, due to its three other digital subchannels, and lack of sports programming.

The European Broadcasting Union (EBU) recommends that its members use 720p50 with the possibility of 1080i50 on a program-by-program basis and 1080p50 as a future option.[5][6][7] The BBC is one of the EBU members transmitting in HDTV. It has not yet made a final decision on picture scanning format. Sveriges television in Sweden, Cyfra+ in Poland, SRG SSR idée suisse in Switzerland, ORF in Austria and VRT in Belgium broadcast in 720p50. All other commercial European HDTV services so far use 1080i50. Broadcasters can also use progressive segmented frame scaling in their 1080i broadcasting so that viewers can see a 1080p image. Unlike NTSC, the ATSC standards do allow for a true 1080p broadcast leaving this battle almost lost on both sides.


From ME

1.  In the hierarchy of video signals based on Japanese standards, 720p (D4) is higher than 1080i (D3).  FYI, D2 and D5 correspond to 480p and 1080p respectively.

2.  My HDTV CRT is 720p capable and normally set to 720p (D4).  However, I haven't figured out what the visual difference is when I switch to D3.

3.  In other words, just try both on the Sky HD cable and kindly let us know your observations.   

[comitatus]

@gearhead000

okie, maybe i should try it out.

@Clondalkin

are there any artifacts i should look for when viewing 1080i over 720p?

thanks guys

[chris69ners]

Im also using a pv70 and in my experience, setting a dvd upscaler to 1080i would always offer a slightly sharper or crisper image compared to 720p. However, I sometimes see slight flickering on very fine details of the program specially when the scene is moving or panning. Mosquito noise is also somewhat more pronounced because of the perceived sharpness.

So from my observation, programs like live shows (sports/news) which by nature look sharp already may be set to 720p, while for movies, 1080i may be used to make it look crisper if you find it a little bit on the soft side.

Its still best that you test and compare both 720p or 1080i settings as long as the source/cable box allows it then check which would give you the best image for a particular program.