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What Frame Rate Is
In video (both Analog and HD), just as in film, images are displayed as Frames. However, there are differences in the way the frames are displayed on a television screen. How Frames are Displayed in Analog Video
Lines and Pixels
A television or recorded video image is basically made up of scan lines or pixel rows. Unlike film, in which the whole image is projected on a screen at once, a video image is composed of lines or pixel rows displayed across a screen starting at the top of the screen and moving to bottom. These lines or pixel rows can be displayed in two ways. The first way is to split the lines into two fields in which all of the odd numbered lines or pixel rows are displayed first and then all of the even numbered lines or pixel rows are displayed next, in essence, producing a complete frame. This process is called interlacing or interlaced scan.
The second method, used in flat panel TVs and computer monitors, is referred to as progressive scan. Instead of displaying the lines in two alternate fields, progressive scan allows the lines to displayed sequentially. This means that both the odd and even numbered lines are displayed in numerical sequence. NTSC and PAL
The number of vertical lines or pixel rows dictates the capability to produce a detailed image, but there is more. It is obvious at this point that the larger the number of vertical lines or pixel rows, the more detailed the image. However, within the arena of analog video, the number of vertical lines or pixel rows is fixed within a system. The current major analog video systems are NTSC and PAL.
NTSC is based on a 525-line or pixel row, 60 fields/30 frames-per-second, at 60Hz system for transmission and display of video images. This is an interlaced system in which each frame is displayed in two fields of 262 lines or pixel rows, which is then combined to display a frame of video with 525 lines or pixel rows. NTSC is the official analog video standard in the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.
PAL is the dominant format in the World for analog television broadcasting and video display and is based on a 625 line or pixel row, 50 field/25 frames a second, 50HZ system. The signal is interlaced, like NTSC into two fields, composed of 312 lines or pixel rows each. Since there are fewer frames (25) displayed per second, sometimes you can notice a slight flicker in the image, much like the flicker seen on projected film. However, PAL offers a higher resolution image and better color stability than NTSC. Countries on the PAL system include the U.K., Germany, Spain, Portugal, Italy, China, India, most of Africa, and the Middle East. DigitalTV/HDTV and NTSC/PAL Frame Rates
Although the increased resolution capability, digital format broadcasting, and high definition video software content standards are a step up for consumers, when comparing HDTV to analog NTSC and PAL standards, the fundamental common foundation of both systems is the Frame Rate.
In terms of traditional video content, in NTSC-based countries there are 30 separate frames displayed every second (1 complete frame every 1/30th of a second), while in PAL-based countries, there are 25 separate frames displayed every second (1 complete frame displayed every 25th of a second). These frames are either displayed using the interlaced scan method or the progressive scan method.
With the implementation of the Digital TV and HDTV, the foundation of how frames are displayed still have their roots in the original NTSC and PAL analog video formats. In soon-to-be former NTSC-based countries, Digital and HDTV are implementing the 30 Frame-per-second frame rate, while soon-to-be PAL-based countries are implementing a 25 Frame-per-second Frame rate.
NTSC-Based Digital TV/HDTV Frame Rate
Using NTSC as a foundation for Digital TV or HDTV, with the frames are displayed as an interlaced image (1080i), each frame is composed of two fields, with each field displayed every 60th of a second, and a complete frame displayed every 30th of a second, using a NTSC-based 30 frame-per-second frame rate. If the frame is in the progressive scan format (720p or 1080p) it is displayed twice every 30th of a second. In both cases, a unique high definition frame is displayed every 30th of a second in former NTSC-based countries.
PAL-Based Digital TV/HDTV Frame Rate
Using PAL as a foundation for Digital TV or HDTV, with the frames are displayed as an interlaced image (1080i), each frame is composed of two fields, with each field displayed every 50th of a second, and a complete frame displayed every 25th of a second, using a PAL-based 25 frame-per-second frame rate. If the frame is in the progressive scan format (720p or 1080p) it is displayed twice every 25th of a second. In both cases, a unique high definition frame is displayed every 25th of a second in former PAL-based countries.
-interlaced scan means:that refers to a video image that is displayed on a screen by scanning or displaying each line (or row of pixels) that make up the image, in an alternate order. In other words, the image lines (or pixel rows) are scanned down the screen from top to bottom, in an alternate order (lines or rows 1,3,5, etc... followed by lines or rows 2,4,6). The entire image is displayed every 30th of a second.
-progressive scan means that is a system in which the image is displayed on a screen by scanning each line (or row of pixels) in a sequential order rather than an alternate order, as is done with interlaced scan. In other words, in progressive scan, the image lines (or pixel rows) are scanned in numerical order (1,2,3) down the screen from top to bottom, instead of in an alternate order (lines or rows 1,3,5, etc... followed by lines or rows 2,4,6). By progressively scanning the image onto a screen every 60th of a second rather than "interlacing" alternate lines every 30th of a second, a smoother, more detailed, image can be produced on the screen that is perfectly suited for viewing fine details, such as text, and is also less susceptible to interlace flicker.
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How HDMI Works
Before the development of high-definition televisions, most TVs displayed pictures in what is now known as standard definition. The picture was roughly square -- its aspect ratio was 4:3. Its resolution, or the number of dots that make up the picture on the screen, was about 704 x 480 pixels. The picture was interlaced -- each piece of the moving image was really half a picture, but the pictures changed quickly enough that the human brain didn't really notice. Finally, older TVs relied on analog signals, which travel as a constantly varying electrical current.
HDTVs, on the other hand, are digital. They use information in the form of ones and zeros. This information travels through cables as distinct electrical pulses. HDTVs have an aspect ratio of 16:9, so the picture is rectangular. They also have a higher resolution -- current HDTV standards allow for resolutions of up to 1920 x 1080 pixels. HDTV signals can also be progressive, meaning that the each frame of the moving image is a whole picture rather than half of one.[Only registered and activated users can see links. Click Here To Register...]
So, compared to standard TVs, HDTVs have a wider screen, more pixels and a faster refresh rate. Often, HDTVs can display more colors than older sets. This means that HDTVs need more data and need it a lot faster than standard-definition TVs do. If an HDTV can receive this information digitally, it also doesn't have to spend time or processing power converting the signal from an analog format.This leads us to HDMI. Created by a group of electronics manufacturers, the HDMI standard is a set of guidelines for creating high-bandwidth connections between digital devices. With the right setup, HDMI can make a significant difference in a home-theater system. The current standard can carry 1080p high-definition signals, and it supports eight channels of uncompressed audio, enough for a 7.1 surround-sound system.HDMI can cut down on the number of cables required to connect components, and it can even reduce the number of
remote-controls needed to watch a movie.
But there's a catch. In order to take advantage of everything HDMI has to offer, all of the components of a home theater have to be compatible with them. Some of the features HDMI touts also don't yet exist in the consumer marketplace. In addition, there's a limit to how long an HDMI cable can be, and some users complain that the limit is too short to support convenient setups. Here, we'll look at exactly what happens inside an HDMI cable, the standard's features and its pitfalls. We'll also examine whether the newest standard, HDMI 1.3, really renders the earlier standards -- which have been out for only a few years -- completely obsolete.
HDMI Signals
One of the common misperceptions about HDMI is that the digital signal is innately superior to an analog signal. In some people's minds, the lack of
analog-to-digital conversion means that the signal is in a pure, undamaged state when it reaches the HDTV set. It's easy to imagine a high-definition, digital signal traveling straight from an HD-DVD player to an HDTV. But signal transmission via HDTV does require an encoding step. HDMI uses transition minimized differential signaling (TMDS) to move information from one place to another. TMDS is a way of encoding the signal to protect it from degrading as it travels down the length of the cable. Here's what happens:
The sending device, such as an HD-DVD
- player, encodes the signal to reduce the number of transitions between one (on) and zero (off). Think of each transition as a sharp drop-off -- as the signal travels, this drop-off can begin to wear away, degrading the signal. The encoding step helps protect signal quality by reducing the number of chances for the signal to degrade.
- One of the cables in the twisted pair carries the signal itself. The other carries an inverse copy of the signal.
- The receiving device, such as an HDTV decodes the signal. It measures the differential, or the difference between the signal and its inverse. It uses this information to compensate for any loss of signal along the way.
HDMI also has the ability to protect data from piracy. It uses high-bandwidth digital copy protection (HDCP) to accomplish this. HDCP is an authentication protocol. Basically, each home-theater device has identification data and encryption data stored on its extended display identification data (EDID) chip. The source device, such as a Blu-ray player checks the authentication key of the receiving device, such as an HDTV. If both keys check out, the sending device moves on to the next step. It generates a new key and shares it with the receiving device. In other words, it creates a shared secret. Ideally, this whole process, known as a handshake, takes place almost instantaneously.
The source device encodes its information using the key it generated it. The receiving device decodes it using the same information. If an unauthorized device tries to intercept the data, the source device stops transmitting. It also makes sure that the key hasn't changed and that the system is still secure every few minutes. All HDMI-compatible devices are required to support HDCP, but the companies that manufacture and distribute high-definition content aren't required to enable it. In the United States, this content-protection ability is mandated by the Federal Communications Commission (FCC).
Next, we'll take a look at the HDMI connector and cable and explore how they carry high-definition signals.
HDMI Connections
So we have:
- Component video carries analog video signals separated into two channels for color and a third for luminance. Component video cables use RCA connectors.
- S-video transmits analog signals using one cable and a four-pin connector.
- DVI, or digital visual interface, is a 29-pin connection commonly used with computer monitors. Unlike composite video and s-video, it carries digital signals.
Many HDTV early adopters rely on DVI, since it hit the market before HDMI did. Since DVI and HDMI both use the TMDS protocol, they're compatible. All you need to connect an HDMI cable to a DVI port is a passive adapter.
The DVI and HDMI connectors have some other similarities. Both use a grid of pins to transmit signals from the cable to the device. While DVI has a 29-pin connector, HDMI's type A connector has 19 pins. A DVI connector also uses a pair of built-in screws to anchor it to the device. HDMI plugs don't have this extra support, and some users have expressed concern that this puts unnecessary strain on the device's circuitry. There's also a miniature version of the HDMI connector for use on smaller devices like digital camcorders as well as a 29-pin type B connector, although most consumer devices use type A. From the HDMI connector's pins, signals travel through twisted pairs of copper cable. Three audio and video channels travel through two pins each, for a total of six pins. The TMDS clock, which allows devices to synchronize the incoming data, travels through one pair of pins. Each of these four total pairs has a shield -- another wire that protects it from interference from its neighbors. The TMDS channels, the clock and the shields make up the bulk of the cable pairs inside the HDMI cable.
he other signals that travel through the HDMI cable need only one pin. One such channel is the consumer electronics channel (CEC). If your devices support it, this channel allows them to send instructions to one another. For example, an HD-DVD player could automatically turn on a home-theater receiver and an HDTV when it started playing a disk. The hot plug detect channel, which uses one pin, senses when you plug in or unplug a device, re-initializing the HDMI link if necessary. The one-pin display data channel (DDC) carries device information and the HDCP encryption information discussed in the previous section. Other channels carry encryption data and electricity to power communication between devices.
The cables themselves come in two categories. Category 1 has a speed of 74.25 MHz. Category 2 has a speeded of 340 MHz. Most consumer cables are the faster category 2 variety.
In addition to the connector and cable, the HDMI standard applies to how TV sets can synchronize sound with video and display color. These capabilities have changed significantly over several revisions to the standard, which we'll compare in the next section.
HDMI Standards and Revisions
The first consumer products with HDMI connections hit the market in 2003. Since then, there have been several changes to the HDMI standard. For the most part, these standards have added support for specific types of content or applications. For example, the first revision, HDMI 1.1, added support for dvd audio
The most recent major revision -- the jump from version 1.2 to 1.3 -- got a lot of attention. New features included a massive increase in bandwidth, support for 16-bit color and support for the xvYCC color standard, which supports additional colors. A new lip-synch feature also reduced that sound and video would fall out of synchronization during playback, making an otherwise immaculate recording look badly-dubbed. Some reports even claimed that any devices that did not have HDMI 1.3 were obsolete.
In some ways, this was just as confusing as it was impressive. Some of HDMI's new abilities don't exist yet in the consumer marketplace. For example, the increased bandwidth -- from 4.9 Gbps to 10.2 Gbps -- can support a refresh rate of 120 Hz, or 120 frames per second. This is twice as fast as the maximum refresh rate in the current HDTV standard. HDMI 1.3 can support 30-, 36- and 48-bit color options known as deep color, but many media players and recorded video materials don't go beyond 16-bit color. Critics also claim that deep color allows HDTV screens to display colors that most people can't even perceive. In addition, while lip synch and one-touch control abilities can be handy, not all HOME THEATER
devices support them. Fortunately, a lack of 1.3 capability doesn't mean your HDTV is useless. HDMI 1.3 is backwards compatible with previous versions. It's like when color TV debuted. People could watch color TV signals on their black-and-white sets -- the TV still worked, but the picture was still in black and white. If your HDTV has HDMI 1.2 but your new components have HDMI 1.3 capabilities, your TV will still work, but without the expanded 1.3 abilities. Since the bandwidth allotments of previous standards are generally enough for most high-definition applications, your picture should still have a pretty good quality.
Another common concern about HDMI is cable length. Although the HDMI standard requires a minimum operable length of 32 feet (10 meters), some users report significantly shorter operable lengths in practice. This is particularly true when transmitting 1080p signals -- the increased demands on bandwidth speeds up the deterioration of the signal. Fortunately, there are amplifiers and extenders that can decode, re-set and re-encode the signal before sending it on the next leg of its journey. For people who are concerned about HDMI's potential limitations, there may be another solution on the horizon. DisplayPort is a new high-definition standard that will cover connections inside devices, like within a laptop, and between devices, like from a media player to an HDTV. DisplayPort hasn't hit the market, though, so whether its quality will surpass that of HDTV is still to be determined.
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standard 1080p
Informatiile despre HDMI sunt foarte interesante si pertinente, ca si tot acest thread. Multumesc pe aceasta cale @gessle.
Pentru @gessle sau cine e in masura sa ne lamureasca, exista un standard 1080p (1920x1080) la 23.976 fps pe HDMI ? Daca da, un televizor LCD, de exemplu, cu interfata HDMI ar trebui sa-l recunoasca si sa-l afiseze ca atare sau il va incadra la 24fps ? In unele documentatii tehnice am vazut 23.98 fps, dar de fapt valaoarea exacta a frame rate-ului este de 23.976. Unul din motivele pentru care intreb acest lucru este faptul ca, aparent, un handshake pe HDMI intre WD TV si un TV LCD de la LG la 1080p 23.976 fps nu s-a incheiat cu succes, in schimb 1080p 24 fps a mers.
Cred ca tot ce este film HD din State vine pe disc cu informatie la acest frame rate si banuiesc ca la acest frame rate este si redat de un player BD.
Ca sa fie pomana completa, niste link-uri catre informatii de standard HDMI ar putea sa ne dea cineva?
Cu multumiri,
vasile101
