What is the difference between a VGA and HDMI cable?
Misunderstanding 1: HDMI is HD, VGA is not
HDMI is the interface standard for video and represents a signal transmission format. It contains video signals, audio signals, and HDCP copyright protection protocols. Currently HDMI supports up to 1920*1080P HD format.
VGA is also a video interface standard, which is the longest used video transmission method in the IT industry. It supports a wide range of resolutions from 640*480 up to 2560*1600.
HD refers to a very high resolution resolution, usually used in the field of television, including: 1280 * 720i, 1280 * 720P, 1920 * 1080i, 1920 * 1080P and other formats.
These three are not equivalent, HDMI and VGA are both signal transmission methods, while HD refers to a video resolution. HDMI supports HD, and VGA also supports it. From the existing resolution, VGA can support resolutions much higher than HD. At present, the command centers of major projects and major institutions (such as military police and television stations) 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 the digital signal bandwidth, and VGA is the analog signal bandwidth, which are defined differently. Cannot be compared directly. As a transmission method of two different technologies, the general comparison bandwidth does not make any sense. If you want to compare, you can compare the same resolution, such as HD, HDMI requires 2.2GHz bandwidth, and VGA only needs 172MHz bandwidth. Why is there such a difference in the middle? First of all, HDMI is a digital signal. When a pulsed wave signal is generated on an analog video, HDMI requires a set of 0, 1 encoded square wave signals for description. The bandwidth required is of course much higher. But high bandwidth does not mean that HDMI transmits more video signals, just because of the difference in transmission technology.
Misunderstanding 3: HDMI signal does not use digital-to-analog conversion, no signal loss; VGA signal requires digital-to-analog conversion, large signal loss
This misunderstanding is very common and spreads widely. However, the authoritative articles of major video technologies (HDMI, DVI, Displayport, etc.) are not mentioned, and should belong to the technical misunderstanding that netizens take for granted. First of all, we must understand the meaning of digital video: digital video signal is a set of 0, 1 encoded square wave signal to describe (encode) the analog signal; since the digital signal is to describe the analog signal, then according to the correct digital coding How can there be a loss when converting analog signals?
Although HDMI does not require digital analog conversion, it still has to undergo digital to digital conversion. No matter what kind of conversion process it is, what is converted into it is, after all, a description of the analog electrical signal.
The signal described by the digital signal is composed of one point, which is inconsistent in the change of the signal, and the change of the analog signal is a continuous curve, so the analog signal gives people a better sense of reality. When a digital signal is converted to an analog signal, the direct output is also a point (the sampling point of the digital signal), and the undescribed part is automatically generated by the conversion program (similar to the 3D anti-aliasing technique) to form a continuous Analog signal waveform. When an analog signal is converted to a digital signal, the continuous analog signal is converted into a digital signal describing a point, and the signal becomes incomplete. From this process, the conversion of digital signals to analog signals is enhanced rather than lost, and analog signals are converted to digital signals with loss.
In the VGA transmission process, the signal loss of the VGA to LVDS driving LCD panel can be neglected, because in the case of the same digital sampling rate at the front and rear ends, these lost signals are originally (when the digital signal is converted into an analog signal) the program automatically The part that is filled is not the loss of the original signal of the digital signal source.
So there is no theoretical basis for the misunderstanding of the loss of digital-to-analog conversion between HDMI and VGA.
Misunderstanding 4: HDMI signal transmission has no loss, VGA signal transmission loss is large
This question involves more complicated discussions. They need to discuss their principles in detail. What is the difference between them?
A. VGA video technology principle:
There are three kinds of early display output standards: MDA, CGA, EGA, all of which are also output with TTL digital signals, but the appearance of the VGA standard output by analog signal immediately eliminated the old display standard until now. VGA has dominated the computer industry for 20 years.
VGA video technology consists in the use of analog component transmission to decompose the video signal into R, G, B primary colors and HV line signals.
This VGA technology, introduced 20 years ago, quickly established its dominance by transmitting extremely high image resolution with a low analog bandwidth. The VGA mode family is very strong and extends a lot of proper nouns. Below is a partial list of the VGA family:
QVGA Quarter VGA 320×240;
VGA 640×480;
SVGA Super VGA 800×600;
XGA Extended G A 1024×768;
SXGA Super Extended GA 1280×1024;
WXGA Wide Extended GA 1280×800;
WXGA+ Wide Extended GA+ 1440×900;
WSXGA+ Wide Super Extended GA+ 1680×1050;
UVGA Ultra VGA 1600×1200;
WUXGA Wide Ultra Extended GA 1920×1440;
WQXGA Wide Quad Extended GA 2560×1600;
From the various high resolutions in the above resolution, the argument that VGA can't be on HD format doesn't need to be refuted. If you want to verify it, let's go to the graphics card to verify it~~~~
B. HDMI principle:
HDMI is a new video standard for the home appliance market in 2002. It divides video signals into R, G, B, H, and V signals. It is encoded by TMDS technology and transmitted through three channels. These three channels transmit R, G, B three primary colors, HV encoding is transmitted in the B signal channel, and the extra positions of R, G, are used to transmit audio signals.
From the figure we can see that HDMI and VGA have undergone the same conversion process. The difference between the two is mainly the difference between HDMI digital signal transmission and VGA analog signal transmission, that is, HDMI and VGA are mainly caused by the difference in transmission process.
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 was no differential transmission technology at the time. In the comparison of similar signals, differential balanced transmission is stronger than unbalanced transmission, which is a positive fact. However, since HDMI and VGA are different signal types and have different signal bandwidths, the difference between this differential and non-differential transmission technology is offset by a lot. With the same resolution, HDMI requires more than 10 times the bandwidth required by VGA. The basic rule of electrical signal transmission is that the higher the bandwidth frequency, the greater the attenuation. So although HDMI's differential balancing technology is stronger than VGA's unbalanced technology, the bandwidth bottleneck limits this advantage. Therefore, the ultimate transmission distance of VGA is 15 meters, and the ultimate transmission distance of HDMI is also 15 meters. From the transmission distance, we can also see the pros and cons of the transmitted image to some extent.
Misunderstanding 5: HDMI is a digital signal, which has a strong error correction capability for signal attenuation.
The HDMI signal uses TMDS technology and is a real-time transmission. The TMDS structure is different from the data packet technology. Only the transmission of data packets has certain signal error correction functions, such as IP packet technology and micro-packet technology of Displayport video.
Misunderstanding 6: HDMI's highest color depth reaches 48, so the effect is good
A technology can not play, the key is his environment, home applications should be practical. Whether HDMI is 24-bit color depth or 48-bit color depth is meaningless for modern families. Constrained by the technology of the liquid crystal panel, the images of the LCD TVs and monitors we see are both 8-bit or 10-bit, 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 network is 8-bit or 10-bit. Whether it is from the signal source or the terminal display device, the high color depth is only a conceptual thing, without any practical value.
If you are looking at the LCD monitor, you can adjust it on the spot, change the 32-bit color of the display property to 16 digits, and see if there is any change in the image in front of you.
Misunderstanding 7: The difference between the HDMI interface and the VGA interface of the DVD player is relatively large, indicating that HDMI is better than VGA.
Regarding this issue, we first look at the host computer. We have no difference in the signal clarity between the HDMI interface and the VGA interface of the computer. Why is there a difference in the DVD player, but there is no difference in the computer host? Simple: cost! !
The video standard used in early DVDs was 600 lines, and at this resolution, the VGA mode circuit was very inexpensive. At the same time, the rapid price cuts of DVD players have also caused DVD drive manufacturers to not increase their prices. The DVD player with HDMI interface is different, and the concept of HDMI can bring huge profits to DVD player manufacturers. The price difference is 5-6 RMB. In order to highlight this concept of price difference, it is inevitable to do a good job of HDMI interface, which leads consumers to think that HDMI effect is far better than VGA effect, but I don't know if it is for concept hype. And are there such a big difference in the manufacturing costs of these two interfaces? Our comparison of the graphics card is proof: the video card with HDMI interface and without HDMI interface, the price gap is not large, the effect gap is not large.
The inherent disadvantages of HDMI video technology:
1. HDMI is an external interface that has limited ability to enhance the resolution and color depth of video.
Although the HDMI specification emphasizes the concept of high bandwidth and high color depth, it is impossible to limit the computer internal signal and the back-end liquid crystal driving circuit in front of HDMI, and it is impossible to achieve a video standard with a lot of room for improvement in the future. It is Displayport. It can be used not only as an interface for external signals (device to device), but also as an internal signal standard (IC to IC), which unifies the internal driving circuit of the computer and the LCD panel. Thereby, the internal signal of the computer directly drives the liquid crystal panel. Similar to notebook LCD technology, notebooks use LVDS technology to drive LCD panels directly.
2. HDMI compatibility is not good
Due to the difficulty of firmware upgrade of HDMI, HDMI1.1 version of the device will not be able to use HDMI1.3 protocol, so if you buy HDMI version 1.3 DVD player, HDMI 1.3 interface LCD TV, but use HDMI1.1 cable, Then you honestly let it run the HDMI1.1 agreement. At the same time, incompatibility and non-display problems may occur between different devices that also have an HDMI interface. HDMI uses an exhaustive method for detecting devices, and has inherent limitations in compatibility.
Overview:
The HDMI interface integrates audio, HDCP copyright protocol, digital video signal, etc. It is indeed more convenient to use than the VGA interface, but HDMI does not occupy a dominant position in terms of video clarity. Therefore, we have seen the HDMI HD concept for consumers in the field of home appliances, and the IT-savvy IT industry does not speculate on the HDMI concept. The misunderstanding caused by these hype, the technical quality of the speculators themselves is stunned: most home appliance salesmen are not clear about some basic common sense, and the propaganda of these concepts is also eloquent. Or quote a section of the technical community's evaluation of HDMI to make this summary:
HDMI is a very good consumer electronics interface, but VESA believes it is not the best solution for PC display interfaces. It has limited performance in terms of resolution and color depth on PC monitors (please check the look-up table, which may fully affect future trends in displays). HDMI is just a very good A/V interface, not a widely used display interface. The HDMI specification does not unify the display interfaces inside and outside the device, and it is primarily intended for consumer electronics devices.
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Post time: Jan-07-2019