Making the Connection: a beginners guide to video connectors.
Visual Interface standards
Visual interface standards are the format and method by which the video signal is transmitted between its source and the display. Simply put it’s the cable that connects the player to the screen we call these video connectors.
These days there are two main high-definition video connectors (visual interfaces), they are HDMI and DVI.
HDMI: High Definition Multimedia Interface.
HDMI was developed by Philips, Panasonic, Sony, Silicon image, Hitachi, and Toshiba. It was officially released in 2002. HDMI is an audio-video interface with a huge bandwidth of 4Gbps which sends the data faster, more reliably, less lossy (loss of data in transmission) which gives you a crisper picture. In technical terminology the specs of HDMI are:
- Supports 1080p.
- Can send up to 8 channels of high-res audio (which is better than DVD audio which only supports 6 channels).
- Supports the colour spaces RGB 4:4:4, YCbCr 4:4:4, YCbCr 4:2:2.
- Supports the video formats: SDTV 720x576i (PAL) 4:3 & 16:9, EDTV 640x480P (VGA) 720x576p (PAL) 4:3 & 16:9, HDTV 1280x720p, 1920x1080i, 1920x1080p) 16:9
Currently the standard HDMI connector is known as “Type A” there is a second connector called “Type B” however this connector has not yet entered production as it is being reserved for future higher-resolution devices.
DVI is made up of 3 types of DVI cables, these cables are DVI-D, DVI-A and DVI-I. the definitions for each cable are as follows:
- DVI-D (digital only) is a faster higher quality image than analogue because of its digital format. All video cards produce a digital video signal at first, which can be converted to an analogue signal if the source has an analogue output. DVI-D eliminates eliminates the need to convert to analogue, making it less lossy. DVI-D sends information using a digital information format called TMDS (Transition minimised differential signalling).
- DVI-A (analogue only) carries a DVI signal to an analogue display. Converting the signal to analogue leads to a loss in quality. Used for older monitors such as CRT and TFT.
- DVI-I (can carry both analogue and digital signals) The digital-to-digital signal sends information using a digital information format called TMDS. If you are trying to connect an analogue source to a digital display you’ll need to buy a converter. The main benefit of DVI-I is that it is a more versatile cable in terms of what it can connect to.
- Single vs Dual link: The DVI-D and DVI-I formats are available in single and/or dual link. TMDS is the digital format used to transfer the information. With the single link there is one TMDS transmitter, Dual link has two transmitters which in effect double the transmission’s power. This means that dual link provides quicker speed and superior signal quality, which means it can display images in higher resolution than single link.
There are also formats which came before the high definition connectors, they are:
This connector only carries a video signal which provides an image only. This cable is usually yellow and the information required to create a picture: the chrominance which is a combination of saturation and hue, the luminance which is the brightness and combines the two in the signal. The main drawback is that you require audio cables in order to get any sound. This type of connector was widely used throughout the 1980’s in older versions of game consoles. It is still widely used for Video, DVD and video games consoles.
S-video is a 4-pin connector which carries two seperate signals, one for the luminance and one for chrominance which delivers a better picture than composite video signals do. Another advantage S-video has over composite is that it can carry audio signals without extra cables.
This type of video came after composite and s-video and carries the picture information in 3 signal carrying wires. One wire carries the luminance and the other two carry the chrominance, the chrominance is split in to two signals, one red and one blue. These are often referred to as YUV, the Y is luma and the U and V are w chrominance signals. The connectors are marked Y which carries the luminance signal(Luma) and Cb and Cr which both carry chrominance signals. The advantage of using component video is that it has a clean image and less colour bleed than the two previous connectors.