1080i is the shorthand name of a format of
High-definition videomodes. The number notates the amount of horizontal scan lines (1080) also known as vertical resolution, while the letter "i" stands for interlaced, a "p" would stand for progressive scan.
1080i is a
high-definition television(HDTV) video mode. The term usually assumes a widescreenaspect ratio of 16:9, implying a horizontal resolution of 1920 pixels and a frame resolution of 1920 × 1080 or about 2.07 million pixels.
frame ratein hertzcan be either implied by the context or specified after the letter i, such as "1080i30", the "30" standing for 30Hz. The two frame rates in common use are 25 frame/s (in countries that use 50 Hz alternating current, traditionally PAL/ SECAMcountries such as in Europe, Australia, much of Asia, Africa) and 30 frame/s (in 60 Hz countries, traditionally NTSCcountries such as United States, Canada and Japan). Both variants can be transmitted by both major digital televisionformats, ATSC and DVB. The European Broadcasting Union(EBU), prefers to use the resolution and field rate separated by a slash, as in 1080i/30 and 1080i/25, likewise 480i/30 and 576i/25.
1080i is directly compatible with CRT-based HDTV sets. 1080i is compatible with newer
720p- and 1080p-based televisions but must be deinterlaced first in order to be displayed on those sets. Of note, a very popular panel size used in mid-range HDTVs is 1366 x 768 and are often advertised as 1080i "compatible" or "HD ready" - however these TVs, while accepting a 1080i signal will scale it down to the panel size of 1366x768 as they are physically incapable of displaying 1920x1080 resolutions. [http://hd1080i.blogspot.com/2006/12/1080i-on-1366x768-resolution-problems.html 1080i on 1366x768 resolution problems ]
Due to revision of the NTSC format when color became available, the frame rate of actual 1080i broadcasts is usually 0.1% slower than is implied. For example, a 1080i30 or "30 Hz" transmission actually displays about 29.97 frames each second. Both the straight 24/30/60 and 23.976/29.97/59.94 frequencies are supported by current standards. In European countries where
PALhas been used, it is common to code 1080i in 25 frame/s which is equal to 50 fields/s.
The interlaced image format 1080i/25 requires about 20% more bit-rate than the progressiveimage format 720p/50 to obtain the same subjective image quality [EBU Recommendation R 124 - [http://www.ebu.ch/CMSimages/en/tec_text_r124-2008_tcm6-60599.pdf Choice of HDTV Compression Algorithm and Bitrate for Acquisition, Production & Distribution] ] .
1080p(in 50 Hz or 60 Hz) is becoming common in production and is foreseen as the future broadcasting standard [EBU Recommendation [http://www.ebu.ch/CMSimages/en/tec_text_r115-2005_tcm6-37869.pdf FUTURE HIGH DEFINITION TELEVISION SYSTEMS] ] . Today EBUrecommends that 720p at 50Hz be used for distribution [EBU Recommendation R 124 - [http://www.ebu.ch/CMSimages/en/tec_text_r124-2008_tcm6-60599.pdf Choice of HDTV Compression Algorithm and Bitrate for Acquisition, Production & Distribution] ] .
* [http://www.ebu.ch/CMSimages/en/tec_doc_t3299_tcm6-23327.pdf High Definition (HD) Image Formats for Television Production] (EBU technical publication)
* [http://reviews.cnet.com/4520-6449_7-6810011-1.html 720p vs. 1080p HDTV: The final word] - CNET Review - December 5, 2007
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