| 词条 | IRE (unit) |
| 释义 |
An IRE is a unit used in the measurement of composite video signals. Its name is derived from the initials of the Institute of Radio Engineers.[1] A value of 100 IRE is defined to be +714 mV in an analog NTSC video signal. A value of 0 IRE corresponds to the voltage value of 0 mV, the signal value during the blanking period. The sync pulse is normally 40 IRE below this 0 IRE value, so the total range covered from peak to trough of an all white signal would be 140 IRE. [2] Note that video signals use the "IRE" unit instead of DC voltages to describe levels and amplitudes. Based on a standard 1 Vpp NTSC composite-video signal that swings from -286 mV (sync tip) to +714 mV (peak video), a 140 IRE peak-to-peak convention is established. One NTSC IRE unit is 7.14mV, where -40 IRE is equivalent to -286 mV, and +100 IRE is equivalent to +714 mV. Note that 0 IRE is equivalent to 0 V. The Black Level is equivalent to 53.57 mV (7.5 IRE)[3] The PAL video signal is slightly different in that it swings from -300 mV to +700 mV, instead. Thus, one PAL IRE unit is 7mV, where -43 IRE is equivalent to -300 mV at the sync tip, and +100 IRE is equivalent to +700 mV at the peak video level. Black level is the same as the blanking level 0 mv (0 IRE) [4][5] The reason IRE is a relative measurement (percent) is because a video signal may be any amplitude. This unit is used in the ITU-R BT.470 which defines PAL, NTSC and SECAM.[6] References1. ^{{cite book|title=Digital television fundamentals: design and installation of video and audio systems|last= Robin & Poulin|first=|authorlink=|author2=Michael Robin |author3=Michel Poulin |year=2000|publisher=McGraw-Hill Professional|location=|isbn=0-07-135581-2|page=17|url=https://books.google.com/books?id=BkCOd_d8_u0C&pg=PA17&dq=IRE+%22composite+video%22&hl=en&ei=HivdTLCEOISClAeYiemaDQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDgQ6AEwAQ#v=onepage&q=IRE%20%22composite%20video%22&f=false }} {{DEFAULTSORT:Ire (Unit)}}2. ^{{cite web|url=https://www.radios-tv.co.uk/Pembers/World-TV-Standards/Line-Standards.html#Units|title=World Analogue Television Standards and Waveforms|accessdate=31 May 2018}} 3. ^{{cite web|url=http://zone.ni.com/reference/en-XX/help/373389B-01/nivms/signals_cvbs/|title=Composite Video Signals (CVBS)|last=|first=|date=|website=National Instruments|archive-url=|archive-date=|dead-url=|accessdate=31 May 2018}} 4. ^{{cite web|url=https://www.embedded.com/print/4009973|title=Measuring composite-video signal performance requires understanding differential gain and phase, Part 1 of 2|author = Cliff Win, Jr.|publisher=National Semiconductor Corporation|accessdate=31 May 2018}} 5. ^{{cite web|title=Vertical Blanking Interval of 625-Line Standard (PAL Colour)|url=http://www.pembers.freeserve.co.uk/World-TV-Standards/VBI-625-PAL.pdf|accessdate=2015-09-03|deadurl=yes|archiveurl=https://web.archive.org/web/20160428234231/http://www.pembers.freeserve.co.uk/World-TV-Standards/VBI-625-PAL.pdf|archivedate=28 April 2016|df=dmy-all}} 6. ^{{cite web|url=http://www.itu.int/rec/R-REC-BT.470-7-200502-I/en |title=BT.470 : Conventional analogue television systems |publisher=International Telecommunications Union |accessdate=28 August 2012}} 5 : Electrical engineering|Broadcast engineering|Video formats|Television technology|ITU-R recommendations |
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