HDTV: 720p, 1080i and 1080p?
It seems like everyone is buying a new HDTV this year. The conversation around the water cooler is full of tech buzzwords. When the HDTV standard in the US was originated by the ATSC (Advanced Television Systems Committee), they defined eighteen different standards, but not all of the standards are in common use.
The standards you should be familiar with for HDTV (High Definition TV) are 720p, 1080i, and more recently 1080p. The number in the format (for example, “720”) are the vertical lines of the screen resolution, and the letter in the format (for example, “p”) represents the technical screen. The letter “p” stands for “progressive” scan and the letter “i” stands for “interlaced”.
HDTV (720p, 1080i, and 1080p) has a widescreen aspect ratio of 16:9 (width:height). EDTV (Enhanced Definition) is a standard definition television (SDTV, the format before HDTV), but with some software “interpolation.” EDTV offers a better picture than SDTV, but not as sharp as HDTV. EDTV uses progressive scan. EDTV sometimes has a 16:9 (widescreen) aspect ratio.
For reference, standard definition television (SDTV, the format before HDTV) has 480 lines of vertical resolution and has an aspect ratio of 4:3. The SDTV signal in the US has historically been an interlaced signal. This means that your TV draws each frame in two passes: one pass for the even horizontal lines and a second pass for the odd lines. The specification is a maximum resolution for the technology, but signal sources are often less than the maximum. For example, a VHS tape has approximately 240 lines of vertical resolution, an over-the-air SDTV broadcast has approximately 330 lines of vertical resolution, and an SDTV DVD has approximately 480 lines of vertical resolution.
The televisions in Europe and Japan have been (and are) of progressive format. A progressive format makes a single pass for all lines. Progressive images look a bit smoother than an interlaced image, especially when there is a lot of movement on the screen, such as sports.
Adding to the confusion, BluRay DVDs do, and later this year satellite TV companies will, broadcast in 1080p. This standard has both the highest number of lines of vertical resolution and the preferred progressive format. Dish Network will begin 1080p satellite transmission in August 2008 with 150 HDTV channels, and DirecTV will begin satellite and Internet transmission in late 2008 with approximately 130 channels of HDTV programming. Satellite companies compress their signal using MPEG-4 techniques, which reduces the bandwidth required for transmission. Currently, the only source material for 1080p is movies, especially movies originally made for IMAX. None of the major networks (ABC, ESPN, etc.) have yet announced 1080p support. Also, Sony PlayStation 3 and Xbox 360 have 1080p games.
HDTV video format: 720p, 1080i and 1080p, higher number is better, right? While 1080i is technically a higher resolution, it’s not the obvious choice. 1080i has 1080 vertical lines of resolution and 1920 horizontal lines of resolution. 720p has 720 lines of vertical resolution and it has 1280 lines of horizontal resolution. But the 720p system is progressively scanned. This compensates for the lower level of resolution. The 1080p signal is the best of both worlds, more picture information with a progressive format.
If your received signal, for example to a satellite receiver, is mostly standard definition, a 1080p TV will not significantly improve your picture compared to a 720p TV. Image quality is fundamentally limited by the source signal (480 lines of vertical resolution). Similarly, if your signal has a 720 source, then the 1080 TV will not improve your picture. All high definition sports broadcasts from Fox, ESPN and ABC are broadcast in 720p.
Some networks have opted for the 1080i format because it provides more picture information, while ABC, Fox, ESPN and National Geographic Channel have chosen the smoother 720p images. HDTV programming on CBS, NBC and other networks is broadcast in 1080i. Newer 1080i or 1080p HDTVs will likely make this type of programming a bit sharper than it would appear on a 720p TV. This becomes more important because as the TV screen gets larger, the visible difference in detail between 720p and 1080i and 1080p displays becomes more apparent. Because of this, most HDTVs larger than 50 inches are 1080p or 1080i.
1080p HDTV System Capabilities:
A 1080p HDTV displays all input signals at 1080p, because this is the unit’s normal resolution. If your system is less than 1080i or 1080p, then a special-purpose chip in your HDTV scales the signal. It will interpolate, as EDTV does with an SDTV signal. If the signal is 1080i, the system will combine the odd and even interlaced frames and display the full signal as 1080p. The resulting performance should be similar to a true 1080p video source.
high definition cable television:
More than 100 million US homes can receive HDTV from their cable system, and all of the top 100 cable markets in the country have HDTV programming available. Unfortunately, most cable providers offer only a few of the 50+ HDTV networks available.
Satellite HDTV:
While the selection of local HDTV channels is generally better on cable than satellite, the major satellite companies offer more national HDTV channels than almost all cable providers. Both DirecTV and Dish Network have promised to offer more than 130 HDTV channels by the end of the year. “Satellite will be limited not so much by how many channels it can carry as by how many it can get,” Bob Scherman, Satellite Business News.
Resume:
Screen resolution for HDTV has become comparable to the microprocessor clock speed for personal computers. Although clock speed is not necessarily a perfect indication of overall system performance, it is often regarded as such by the consumer.
Interestingly, when a group of experts, the SMPTE (Society of Motion Picture and Television Engineers), recently ranked the importance of resolution, it ranked fourth. SMPTE ranked contrast ratio, color saturation, color temperature, and gray scale above resolution in importance. The Imaging Science Foundation reached a similar conclusion. However, most HDTV manufacturers include premium features, such as improved contrast ratio with higher screen resolutions, in their top-of-the-line HDTVs. So if you buy a set with the best screen resolution, you’ll most likely receive the best lineup from the manufacturer for other important screen criteria.
Prices have fallen significantly in the last two years, but it appears that the rate of price reduction has slowed significantly recently. “TV shoppers visiting mass retailers may be more concerned with getting a low price and may not seek expert advice. However, TV shoppers should keep in mind that the lower prices they find in The mass stores are mainly due to the fact that these stores tend to carry second-tier brand TVs, rather than major brands like Sony or Panasonic.When you compare the price of a specific TV model at each type of retailer, the prices are surprisingly similar,” said Larry Wu of JD Power.
And as a final note, be sure to take into account the audio side of your system. George Lucas (Star Wars) once said that audio is half the experience of watching a movie. It is also true for a good game of football or basketball.
