At present, many consumers are misled by some intentional or unintentional technologies, resulting in some technical misunderstandings, which spread everywhere on the Internet. This paper collects these popular views and explains them one by one. Please correct me if there is anything wrong.
The misunderstanding of netizens is as follows:
Misunderstanding1; HDMI is high definition, VGA is not.
HDMI is an interface standard for video, representing a signal transmission format. It includes video signal, audio signal and HDCP copyright protection protocol. At present, HDMI supports the highest HD format of 1920* 1080P.
VGA is also a video interface standard, which is the longest used video transmission mode in IT industry. It supports various resolutions from 640*480 to 2560* 1600.
Hd refers to a high-definition resolution, which is usually used in TV field, including: 1280*720i, 1280*720P, 1920* 1080i,1920 */kloc.
These three relationships are not equivalent. Both HDMI and VGA are signal transmission methods, while HD refers to a video resolution. HDMI supports HD, so does VGA. Judging from the existing resolution, VGA can support much higher resolution than HD. At present, the command centers of major projects and institutions (such as military police and television stations) all use VGA technology to transmit ultra-high-definition large-screen images.
Misunderstanding 2; HDMI bandwidth is high, VGA bandwidth is low. So HDMI is better than VGA.
The bandwidth of HDMI is digital signal bandwidth, and VGA is analog signal bandwidth. The two definitions are different. Can't compare directly. As two different transmission methods, it is generally meaningless to compare bandwidth. If you want to compare, you can compare when transmitting the same resolution, such as high definition. HDMI needs 2.2GHz bandwidth, while VGA only needs 172MHz bandwidth. Why are there such differences between them First of all, HDMI is a digital signal. When generating pulse radio wave signals on analog video, HDMI needs a set of 0, 1 coded square wave signals to describe it, which of course requires much higher bandwidth. However, high bandwidth does not mean that HDMI transmits more video signals, but the transmission technology is different.
Misunderstanding 3; HDMI signal does not need digital-to-analog conversion, and there is no signal loss; VGA signal needs digital-to-analog conversion, and the signal loss is large.
This misunderstanding is very common and universal. But the authoritative articles of major video technologies (HDMI, DVI, Displayport, etc. ) are not mentioned, it should be a technical misunderstanding that netizens take for granted. First of all, we should understand the meaning of digital video: digital video signal is a set of square wave signals encoded by 0 and 1 to describe (encode) analog signals; Since the digital signal describes the analog signal, how can the analog signal be lost when it is converted according to the correct digital coding?
Although HDMI does not need digital-to-analog conversion, it still needs digital-to-analog conversion. No matter how it is converted, what it is converted into is, after all, the description of analog electrical signals. Their relationship is as follows:
The signal described by digital signal is composed of points, which is discontinuous in the change of signal, while the change of analog signal is a continuous curve, so the analog signal gives people a better sense of reality. When a digital signal is converted into an analog signal, the points (sampling points of the digital signal) are directly generated, and the undescribed parts are automatically generated by the conversion program (similar to the anti-aliasing technology in 3D), forming a continuous analog signal waveform. When analog signals are converted into digital signals, continuous analog signals are converted into digital signals describing points, and the signals become incomplete. From this process, the conversion from digital signal to analog signal is enhanced rather than lost, while the conversion from analog signal to digital signal will be lost.
In the process of VGA transmission, the signal loss from the LCD panel driven by VGA to LVDS can be ignored, because these lost signals are originally the automatic filling part of the program (when digital signals are converted into analog signals), rather than the original signal loss of the digital signal source. As shown in the figure:
Therefore, there is no theoretical basis for misunderstanding about the digital-to-analog conversion loss between HDMI and VGA.
Misunderstanding 4; There is no loss in HDMI signal transmission, and there is a great loss in VGA signal transmission.
This problem involves a complicated discussion, so we need to discuss their principles in detail and compare their differences.
Principle of VGA video technology;
There are three early display output standards: MDA, CGA and EGA, all of which are TTL digital signal output. However, the appearance of VGA standard for analog signal output immediately eliminated the old display standard. Until now, VGA has dominated the computer industry for 20 years.
VGA video technology is to decompose the video signal into three primary colors of R, G and B and HV line field signals by adopting analog component transmission mode.
This technology, which appeared 20 years ago, led to the rapid establishment of the dominant position of VGA video technology, which can transmit extremely high image resolution with very low analog bandwidth. Its VGA mode family has grown greatly, and many proper terms have been expanded. The following is a partial list of VGA series:
QVGA quarter VGA 320×240；;
VGA 640×480；
SVGA Super VGA 800×600；;
XGA extended GA1024× 768;
SXGA Super Extended GA1280×1024;
WXGA wide extension ga1280× 800;
WXGA+ extended ga+1440× 900;
WSXGA+ wide hyperextension ga+1680×1050;
UVGA Ultra VGA 1600× 1200；
WUXGA wide over-extended ga1920×1440;
WQXGA wide four-way extension ga 2560×1600;
From the various high resolutions in the resolution table above, I don't need to refute the statement that VGA can't be in HD format. If you really want to verify, please go to the graphics card settings to verify ~ ~ ~
B) HDMI principle:
HDMI is a new video standard in the home appliance market in 2002. It divides video signals into five types: R, G, B, H and V, and uses TMDS technology to encode them and transmit them through three channels. These three channels transmit the three primary colors of R, G and B, HV coding is transmitted in the B signal channel, and the redundant positions of R, G and V are used to transmit audio signals.
HDMI and VGA went through the same conversion process. The difference between them is mainly the difference between the digital signal transmission of HDMI and the analog signal transmission of VGA, which means that the difference between HDMI and VGA is mainly caused by the different transmission technology.
HDMI uses TMDS technology to transmit signals (TMDS is the minimum differential transmission technology), and VGA uses analog unbalanced transmission technology. Because VGA video technology was born 20 years ago, there is no differential transmission technology. It is a certain fact that differential balanced transmission is stronger than unbalanced transmission in the comparison of similar signals. However, because HDMI and VGA are different signal types and have different signal bandwidths, the differences between differential and non-differential transmission technologies offset a lot. At the same resolution, HDMI is 10 times higher than the bandwidth required by VGA. The basic law of electric signal transmission is that the higher the bandwidth frequency, the greater the attenuation. So although the differential balance technology of HDMI is stronger than the unbalanced technology of VGA, the bandwidth bottleneck restricts this advantage. So the limit transmission distance of VGA is 15m, and that of HDMI is 15m. From the transmission distance, we can also see the quality of the transmitted image to a certain extent.
Misunderstanding 5; HDMI is a digital signal, which has a strong error correction ability for signal attenuation.
HDMI signal adopts TMDS technology and belongs to real-time transmission. TMDS structure is different from data packet technology, and only the transmission of data packets has certain signal error correction function, such as IP packet technology and micro-packet technology of Displayport video.
Misunderstanding 6; The highest color depth of HDMI reaches 48 bits, and the effect is good.
Whether a technology can be played depends on its environment. Home applications should be practical. HDMI, whether 24-bit color depth or 48-bit color depth, is meaningless to modern families. Limited by the LCD panel technology, the images we see on LCD TVs and monitors are all 8-bit or 10, because the current LCD panel technology can only achieve this step.
Not only the LCD panel, but also the HD source we downloaded on the Internet is 8-bit or 10. No matter from the signal film source or terminal display equipment, high color depth is only a conceptual thing and has no practical value.
If it is in front of a liquid crystal display, it can be adjusted on the spot to change the 32-bit true color of the display attribute to 16. See if the image in front of you has changed.
Misunderstanding 7; The signal gap between HDMI interface and VGA interface of DVD player is relatively large, which shows that HDMI is better than VGA.
On this issue, let's first look at the computer mainframe. There is no difference in signal clarity between HDMI interface and VGA interface of computer host. Why is there a difference between a DVD player and a computer host? Simple: cost! !
The video standard used in early DVD was 600 lines. At this resolution, the circuit cost of VGA mode is very low. At the same time, the rapid price reduction of DVD players also leads DVD players not to increase costs. The DVD player with HDMI interface is different, and the concept of HDMI can bring huge profits to DVD player manufacturers. The price difference reaches 500-600 RMB. In order to highlight the concept of price difference, it is necessary to do a good job of HDMI interface, which leads consumers to mistakenly think that HDMI effect is far better than VGA effect, but this is for concept hype. And is there such a big gap between the manufacturing costs of these two interfaces? The comparison between us and the graphics card is evidence: the price difference between the graphics card with HDMI interface and the graphics card without HDMI interface is not big, and the effect difference is not big.
Inherent disadvantages of HDMI video technology:
1) HDMI is an external interface, which has limited ability to improve video resolution and color depth.
Although the HDMI specification book highlights the concepts of high bandwidth and high color depth, it cannot be greatly improved due to the limitation of the internal signal of the HDMI front-end computer and the back-end LCD driving circuit. The video standard that can really improve in the future is Displayport, which can not only be used as an interface for external signals (device-to-device), but also become an internal signal standard (IC-to-IC), unifying the driving circuits of computers and LCD panels. So as to directly drive the liquid crystal panel through signals inside the computer. Similar to the LCD technology of notebooks, notebooks directly use LVDS technology to drive LCD panels.
2) HDMI compatibility is not good.
Due to the difficulty in upgrading the firmware of HDMI, devices with HDMI 1. 1 version will not be able to use the HDMI 1.3 protocol, so if you buy a DVD player with HDMI 1.3 version and an LCD TV with HDMI 1.3 interface, you will be old. At the same time, different devices with the same HDMI interface will be incompatible and cannot be displayed. HDMI uses an exhaustive method to detect devices, which has inherent limitations in compatibility.
Summary:
HDMI interface integrates audio, HDCP copyright agreement, digital video signal, etc. It is indeed more convenient to use than VGA interface, but from the perspective of video clarity, HDMI does not occupy much advantage. Therefore, we can see that consumers are crazy about the concept of HDMI HD in the field of home appliances, while the technical and pragmatic IT industry is not crazy about the concept of HDMI. The misunderstanding caused by these speculations and the technical quality of the speculators themselves are dumbfounded: most home appliance salesmen don't even know some basic common sense, and they are eloquent when selling these concepts. Let's quote a technical evaluation of HDMI to make this summary:
HDMI is a good interface for consumer electronic products, but VESA thinks it is not the best solution for PC display interface. The performance in the resolution and color depth of PC monitor is limited (please check the comparison table, which may completely affect the future development trend of the monitor). HDMI is just an excellent A/V interface, not a widely used display interface. HDMI specification can not unify the internal and external display interfaces of devices, mainly for consumer electronic devices.