DVI/HDMI/VGA/SDI Video Signal Connectors in Digital Signage

Posted on by FS.COM

Nowadays DVI and HDMI connections become more and more widely used in digital signage, we are usually asked that which is better, DVI (or HDVI) or VGA and even or SDI? I think there is no clear answer to this problem.

First, there are some knowledge about these elements we need to know. DVI and HDMI are the same as one another regarding image quality and resolution. The main differences HDVI and DVI are that HDMI carriers audio and video signal; moreover HDMI uses different types of connectors. And both the HDMI and DVI use the same encoding technology, and for that reason DVI source can be connected to an HDMI connector or display, with a DVI/HDMI cable, with no use of signal converter. SDI is a professional video transmission interface, commonly used in broadcast video equipment. SDI and HDMI interface all support digital video transmission which without compressed. HDMI and SDI have different applications and they will not have a conflict. HD-SDI can reach up to 1080I and the latest version of the 3G-SDI, it can up to 1080P. VGA signal type is analog signal, the video output interface for the 15-pin female socket, and the input interface is 15-pin male plug.

What are the difference between DVI, HDMI, SDI and VGA?

DVI, HDMI, SDI and VGA Videos are all video signals which support a variety of resolutions, each one of them deliver the signal from source to display in different ways. The main differences is that DVI/HDMI delivers the signal in a digital format. VGA is an analog format, which deliver the signal, not as a digital stream, but as a set of carrying voltages representing the red, green and blue components of the signal. The figure below represents the in turn: DVI, HDMI, SDI and VGA.

DVI HDMI SDI VGA

DVI, HDMI and VGA deliver signals as red, green, and blue color components, together with sync information. The DVI/HDMI standard delivers these along three data channels in a format called T.M.D.S, which stands for “Transmission Minimized Different Signaling” . This basically involves a blue, red and green sync that are added, and separate the channels.

VGA is delivered, almost similarly, with the color information slit up three ways. However, VGA uses a color difference type signal, which includes Luminance, the green red or blue channel, representing the total brightness of the image. The sync pluses for both horizontal and vertical are delivered on the Y channel.

SDI is divide into SD-SDI and HD-SDI, and now among high definition digital television production equipment, it has been mainly connection ways. SDI can not transmit compressed digital signals directly, digital video recorder, hard disk and other devices that can record compressed signal replay and must be decompressed and according to SDI connector and then enter into the system. If you repeated the compression and decompression,  it will cause the image’s quality.

HDMI, DVI, SDI and VGA signal types are similar fundamentally, because they break up the image in similar ways, and deliver the same type of information to the display. How the differ, as we’ll see, it depends on a great extent upon the particular characteristics of the source and display devices, and depend upon cabling as well.

What is better Digital or Analog?

Digital signal transfer, it is assumed that s error-free, while analog VGA signals are always subject to some amount of degradation and information loss. There is an element of truth to this argument, but it tends to back fire in real-world testing. First, there is no reason to get signal degradation of an analog VGA signal in digital signage installation where the distance between the player and the screen is short. Digital signage installation in a large retail or education facility for example can present a challenge for analog cabling. But, it is a flawed assumption to suppose that digital signal handling is always error-free. DVI and HDMI signals aren’t subject to signal error correction like downloading a file; once information is lost, it’s lost for good. That is not a consideration with well-made cable over short distances, but can easily become a factor at long distance. We know that SDI and HDMI both support digital video transmission without compression, the differences are that HDMI need to 19 cables to transmit and the SDI just need 75Ω coaxial cables. HDMI transmit only 40 meters at most currently and the SDI can transmit 120-400 meters.

The Answer: It Depends

So, which is better, DVI, HDMI, SDI or VGA? The answers unsatisfying, but the truth is that it depends. It depends upon your source player, type of cable, type of display and the distance, and there’s no good way, in principle, to say in advance whether the digital or the analog connection will draw a better picture. You may find that some digital signage player looks better through its DVI or HDMI output, while a different player using VGA output better image through its RGB cable, and SDI output better video than others. On the same display. Some installers reports ghosting/blurriness with text using analog and when switching to digital interface made things much crisper. On the other hand, other installers who used DVI/HDMI long cable found that the text was blurry, colors were off and the image didn’t scale to fit correctly and got no issues at all with VGA.

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