Detailed explanation of DVI, HDMI and VGA interfaces is worth a look

In the security industry, high-definition device interfaces are often contacted. The high-definition interfaces commonly encountered are DVI, HDMI, and VGA.

We generally understand the concept of high-definition interfaces on the Internet or in technical magazines, but because of the general confusion in writing some technical articles, there are some technical misunderstandings about these interfaces.

So what's the difference between these three interfaces? Put aside your misunderstanding, correctly understand DVI, HDMI, VGA.

VGA, DVI, HDMI concepts and features

1.VGA

VGA (Video Graphics Array) also has a name called D-Sub. The VGA interface has a total of 15 pins and is divided into 3 rows with 5 holes in each row. It is a widely used interface type on graphics cards. Most graphics cards have such interfaces. It transmits red, green, and blue analog signals as well as synchronization signals (horizontal and vertical signals). Use VGA to connect the device, the cable length should not exceed 10 meters as far as possible, and pay attention to whether the connector is firmly installed, otherwise it may cause ghosting in the image.

VGA supports simultaneous display of 16 colors or 256 gray levels at a higher resolution of 640 × 480, and simultaneous display of 256 colors at a resolution of 320 × 240.

2.DVI

DVI is the digital video interface. It is a high-speed technology for transmitting digital signals without digital-to-analog conversion. There are various specifications of the DVI interface, common ones are DVI-A, DVI-D and DVI-I. DVI video transmission avoids digital-to-analog conversion at the transmitting end (generally a graphics card) and analog-to-digital conversion at the receiving end (generally an LCD display) during the transmission of analog video signals, and also avoids noise interference during the transmission of analog signals Problem, so the image is lossless.

Features:

1. The digital signal avoids the analog / digital conversion process, the signal is not attenuated, and the color is more pure and lifelike.

2. Only video signals are transmitted, no audio signals are transmitted.

3. Support multiple formats, including all 1920 * 1080 high-definition formats.

4. The effective transmission distance is only about 5 meters.

3.HDMI

High Definition Multimedia Interface (English: High Definition Multimedia Interface, HDMI) is a digital video / audio interface technology. It is a dedicated digital interface suitable for image transmission. It can simultaneously transmit audio and video signals. The maximum data transmission speed is 5Gbps. . At the same time, there is no need to perform digital / analog or analog / digital conversion before signal transmission.

Features

1. Can transmit uncompressed audio signals and high-resolution video signals, digital signals, high quality.

2. Improve data transmission bandwidth up to 5Gbps.

3, can support up to 1080P video.

4. Theoretical 20m, the actual is generally about 3m.

5. Simultaneous transmission of audio, video and copyright protection is very popular in the field of consumer electronics.

6. HDMI is an external interface, which has limited ability to improve the resolution and color depth of the video.

7, HDMI compatibility is not good.

Some misunderstandings about VGA, DVI, HDMI

Misunderstanding 1: HDMI is high definition, VGA is not.

These three are not equivalent. Both HDMI and VGA are signal transmission methods, while HD refers to a video resolution. HDMI supports HD, as does VGA. HDMI currently supports up to 1920 * 1080P high-definition format, and VGA supports various resolutions from 640 * 480 to up to 2560 * 1600. HD refers to a resolution with extremely high definition, including: 1280 * 720i, 1280 * 720P, 1920 * 1080i, 1920 * 1080P and other formats. From the existing resolution, VGA can support resolutions much higher than HD.

Myth # 2: High HDMI bandwidth and low VGA bandwidth. So HDMI is better than VGA.

The bandwidth of HDMI is the bandwidth of digital signals, and VGA is the bandwidth of analog signals. These are the transmission methods of two different technologies. If you want to compare, you can compare them with the same resolution, such as high-definition, HDMI requires 2.2GHz bandwidth, and VGA only needs 172MHz bandwidth. But high bandwidth does not mean that HDMI transmits more video signals, it is just because of different transmission technologies.

Misunderstanding 3: HDMI signals do not require digital-to-analog conversion, and there is no signal loss; VGA signals require digital-to-analog conversion, and signal loss is large.

Although HDMI does not require digital-to-analog conversion, it still has to go through digital-to-digital conversion. No matter what kind of conversion process it is, what it is converted into, after all, it is a description of analog electrical signals. Their relationship is as follows:

The signal described by the digital signal is composed of points, which are incoherent in the change of the signal, while the change of the analog signal is a continuous curve, so the analog signal gives a better realism. When a digital signal is converted to an analog signal, the points that come out directly (sampling points of the digital signal), and the parts that are not described will be automatically generated by the conversion program (similar to 3D anti-aliasing technology) to form a continuous Analog signal waveform. When analog signals are converted to digital signals, continuous analog signals are converted into digital signals describing each point, and the signal becomes incomplete. From this process, there is an increase rather than a loss in the conversion of digital signals to analog signals, and there is a loss in the conversion of analog signals to digital signals.

In the process of VGA transmission, the signal loss of the VGA to LVDS driving LCD panel can be ignored, because when the front and rear digital sampling rates are the same, these lost signals are originally (when converting digital signals to analog signals). The filling part is not the loss of the original signal of the digital signal source. As shown in the figure:

Myth 4: HDMI is a digital signal, and it has a strong ability to correct signal attenuation.

The HDMI signal uses TMDS technology, which belongs to real-time transmission. The TMDS structure is different from data packet technology. Only the transmission of data packets has certain signal error correction functions, such as: IP data packet technology and Displayport video micro-packet technology.

Misunderstanding 5: The maximum color depth of HDMI reaches 48 bits, so the effect is good.

Constrained by LCD panel technology, the images we see on LCD TVs and monitors are either 8-bit or 10-bit, because current LCD panel technology can only reach this step. Not only the LCD panel, but also the high-definition film source we download on the Internet is also 8-bit or 10-bit. Regardless of the signal source or the terminal display device, high color depth is only a conceptual thing, without any practical value. If everyone is in front of the LCD display, you can adjust it on the spot and change the 32-bit true color of the display attribute to 16-bit to see if the image in front of you has changed.