From the perspective of the development history of the display video interface, the common interface of the display card is theoretically possible to reach picture and signal transmission through the adapter(built-in conversion circuit), but because the transfer protocols, interface definitions and working principles are not the same, also avoids the loss of video signal and distortion of display quality after using the adapter, therefore, it is recommended that you directly use the port corresponding to the original interface and the transmission cord of the interface for video transmission.

The development history of the display video interface

Common display interface specifications

  •      VGA (Video Graphics Array)
  •      DVI(Digital Visual Interface)
  •      HDMI(High-Definition Multimedia Interface)
  •      DP(Display Port)

    • Display output conversion description

    ● The development history of the display video interface

    The development history of the display video interface is: VGA -> DVI -> HDMI -> DP

    VGA Icon

    DVI-D Icon

    HDMI Icon

    DP Icon
    vga adapter dvi adapter hdmi adapter dp adapter

    ● Common display interface specifications

    o VGA (Video Graphics Array) Array Graphics Interface

    Video interface with 15 pins is mainly used for old-fashioned computer output. VGA transmission uses analog signaling protocol. In the case of the display card producing digital signal such as HDMI, DP while the monitor is an analog VGA port, using the adapter to convert the signal to the VGA interface is equivalent to undergoing a digital-to-analog conversion and an analog-to-digital conversion.

    o DVI（Digital Visual Interface）

    The DVI interface transmits digital signals, which can transmit large resolution video signal. Connection between computer graphics and monitor via DVI no conversion needed, so there is no signal loss.

    DVI has five specifications

    DVI has three interfaces

    1. DVI-A (12+5)

    2. single link DVI-D（18+1）

    3.double link DVI-D（24+1）

    4. single link DVI-I（18+5）

    5. double link DVI-I（24+5）

    1. DVI－Analog（DVI-A）interface

    2. DVI-Digital（DVI-D）interface

    3. DVI-Integrated（DVI-I）interface

    Among them, DVI-I and DVI-D are divided into “single link” and “double link”, the exact comparison form is as follow

    DVI interface type

    Signal type

    Pin number

    Graphic example

    DVI-I single link

    Digital/Analog

    18+5

    dvi

    DVI-I double link

    Digital/Analog

    24+5

    dvi

    DVI-D single link

    Digital/Analog

    18+1

    dvi

    DVI-D double link

    Digital/Analog

    24+1

    dvi

    DVI-A

    Analog

    12+5

    		 dvi

    o HDMI（High-Definition Multimedia Interface）

    HDMI is a digital interface for transmitting images and sounds, which can send uncompressed audio and video signals, so the image quality is basically the same as that achieved by DVI interface transmission. HDMI interface also can transmit audio signals. If the display also has an audio function, HDMI interface can simultaneously transmit the computer image and audio signals to the display.

    o DP（Display Port）

    Display Port is a display interface launched by VESA (Video Electronic Standard Associate). As the successor to DVI, Display Port supports the transmissions of high-definition audio signals while transmitting the video signals, and supporting higher resolution and refresh rate. It can support single-channel, one-way, four-wire connection, data transmission rate of 10.8Gbps, enough to transmit uncompressed video and related audio, and also supports 1Mbps bidirectional secondary channel for device control, in addition to support 8-bit and 10-bit color.

    ● Display output conversion description

    o VGA output to monitor HDMI port

    VGA can’t be directly converted to HDMI, VGA is an analog signal, and HDMI is a digital video signal, it needs to convert the signal through the adapter, after the conversion, the signal is easy to lose signal and reduce the image quality.

    o HDMI output to monitor VGA port

    HDMI can’t be directly converted to VGA, because HDMI is a digital interface with high-definition audio, and VGA is analog interface, which is only used for video or image transmission, like monitors or other video surveillance devices are VGA interface. If you use the HDMI to convert to VGA, the converted image will generally have color cast and image quality attenuation.

    o DVI output to monitor HDMI port

    HDMI is a multifunctional transmission interface derived from the basis of DVI technology, which can adapt to the high frequency width of HD video stream. HDMI and DVI both transmit signals through TMDS, the number of TMDS channels can be regarded as the only difference between HDMI and DVI, so DVI is also a part of HDMI protocol respectively transmitting three TMDS digital signal streams and a 7.1-sound-track digital audio stream without decoding. When DIV converts to HDMI interface, since DVI was only designed for digital video transmission, so it didn’t reserve for audio interface at that time, that is only can transmit video signals, it can’t transmit audio and video signals at the same time like HDMI does.

    o HDMI output to monitor DVI port

    HDMI and DVI are both digital interface, but there are still some differences between them. DVI interface was born very early, when it was born the HD still hadn’t been come up with, so DVI interface was actually not ready for HD, but a pure digital interface only for transmitting video signals, and HDMI is a digital-HD audio interface, when it transmits HD video signals, it also can send uncompressed audio signals. Due to the function of these two interfaces is different, it is not recommended to use adapter.

    o DP output to monitor HDMI port

    The bandwidth of the DP interface is relatively large. Strictly speaking, the video part in DP and HDMI is developed from DVI and the basic signal mode is the same. DP and HDMI transmit high-frequency signal so that the demand for transmission cable is relatively higher. After the adapter conversion, there may still be picture distortion, signal interruption and even no signal output.