Video Systems and Understanding Quality

In Uncategorized by tfwm

How can you assure yourself that you are maintaining the highest quality at which your video system can perform?

It starts by being sure your video system has the appropriate tools and is connected properly for optimum performance. However, even if your system has the appropriate components and is connected with the appropriate ‘glue’, it may not be able to obtain the quality you may require. Let’s evaluate some basic formats of video first to find out if the format you are using (or contemplating) is capable of your goals, then in later articles we will discuss some specific tools that can help you to achieve the highest quality video you can from the equipment that you have.

Let’s start with standard definition video formats, including a brief description of some of the technical issues of each format. Analog systems do suffer from various distortions because of their analog nature. Signals are represented by sine waves which have some degree of distortion as they pass through every component in the system. Digital systems because they are digital 0’s and 1’s offer far less distortions, but as you will see, digital systems may also have quality issues to consider as well. We will discuss analog formats, NTSC, S-Video, and component analog. We will then delve into Standard Definition Digital formats, DV and Component Digital.

Video standards start at good old fashioned NTSC- which I like to term ‘Never Twice the Same Color’. Actually NTSC stands for National Televisions Standards Committee, but Never Twice the Same Color seems to fit much better. I suggest this because every standard television set in NTSC has four knobs on it to adjust color (contrast, brightness, color and hue). The problem is that most consumers (and some professionals) do not know how to calibrate their monitors for accurate color reproduction- hence Never Twice the Same Color. So no matter how carefully you select a color in a graphic or scene, you have no idea how well that color will be reproduced on the variety of television sets that will play it back.

NTSC recently celebrated its 50th birthday. It was the first commercially successful color television system in the world. For over 50 years the television industry has been able to achieve some very high quality images with this standard, but in the house of worship NTSC is quite inadequate to achieve most goals especially when projecting large images to a large venue projector.

The NTSC system works in an ‘encoded’ format, meaning that the luminance (black and white) and chroma (color portions of the picture) are encoded together and transmitted down one video cable. I like to compare the video cable to a water hose, and NTSC has only one hose for the signal transmission.

The problems with NTSC are the encoding artifacts and loss of resolution. This is quite easy to describe- just think of someone wearing a shirt with fine vertical or horizontal lines in it, and the resulting moir pattern one sees on television. This loss of detail is also visible in other things in an image, such as text from computer graphics, worship software programs or MS PowerPoint files.

This quite simply is a limitation of the television system, and even the best equipment operating in the NTSC standard will fall short, especially when sending the signal to a large venue video projector. That is why a computer image in native computer resolution looks so much better than a scan-converted NTSC image. So, if your main goal is graphics quality you will find that NTSC is very poor for your needs. But if your requirements are to play back video or camera signals, NTSC ‘could’ be adequate.

The next step up in video signals is S-Video, which keeps the luminance and chrominance channels separated. S-Video is the first level of component video, and does not have the encoding artifacts that NTSC adds to the signal. It is far more appropriate than NTSC for many applications, including Projection. S-Video does have a small increase in price for some equipment you may require, specifically the production switcher. This increased quality should be easy to see with the naked eye. Simply connect a camera to a projector or high quality monitor with NTSC and S-Video cables to two inputs, focus the camera on an object with a lot of detail in it and switch between the inputs.

You may be familiar with the S-Video connector – a small mini din connector which must be lined up very specifically to mate the connectors or connector damage can easily occur. S-Video connectors and the two small gauge video cables are appropriate for reasonable distances, but are not suitable for distance approaching 100 feet.

If you do require cable runs longer than 100 feet, I recommend that you use two S-Video breakout cables that have two BNC connectors on one side and a traditional S-Video connector on the other. Then, use two high quality video cables to connect the adapter cables together. Longer runs may also require equalizing amplifiers to further correct the signals and provide more acceptable resolution.

The next level of video is component analog, known as RGB, Betacam, Y R-Y B-Y, Y Pr Pb and also RGBHV. These are different ‘flavors’ or names for component video, but they all have some similarities- mainly that there are three pipes for the signals. Component analog does not have the encoding problems of NTSC, and does provide much higher quality transmission of video signals – especially graphics.

RGB and RGBHV are generally related to computer applications. RGB stand for the Red, Green and Blue channels, H and V are for Horizontal and Vertical Sync. These two variants of component can also allow transmission of High Definition signals, such as those used in HDTV systems. The 15 pin connector (HD-15) that connects your computer to a display or projector can be a variety of resolutions, and sometimes is broken into 5 different video cables for longer distance runs. These are often used to send signals to projectors several hundred feet from the control room or source.

Betacam, Y R-Y B-Y and Y Pr Pb are all the same signal. Y stands for the luminance channel, R-Y is the red channel minus luminance and B-Y is blue minus luminance. Y Pr Pb is another name for the same signal, and is often used for consumer electronics such as DVD players and monitors. Some new broadcast equipment also uses Y Pr Pb input labels in current products. Again this signal is transmitted down three wires/pipes, and three pipes can carry more water- so your signals will be of higher quality. Generally speaking signals labeled in this fashion are standard definition, but are the highest quality signals that analog television systems can obtain.

Component analog is more appropriate for applications that require graphics and moving video, such as an Image Magnification (IMAG) system with multiple cameras that also integrate graphics in lower third windows or a mix between graphics and video. The equipment required to build a component system is a little more expensive, but the quality improvement is worth the investment to most media ministries when their performance requirements demand it. One key piece of gear that will have a significant price increase to provide component output is the computer scan converter. These will usually fall in the $1,000 to $2,000 budget range for high quality units.

The next level of video is digital video. DV or Digital Video is commonly associated with mini DV camcorders. This signal is also called Firewire, IEEE-1394, 1394 and iLink. These are all names for the same signal. In this format the signal is component digital at 8 bit resolution, 4:1:1. The signal is represented as digital 0’s and 1’s.

8 bit resolution means that 8 bits or 256 levels are used to define the levels of black to white or colors. This can cause a quality problem, especially when looking at gradient backgrounds that have small luminance or chroma changes in them and appear to have stair steps in them. This is inherent in the format, and can be difficult or impossible to correct- sometimes it is helpful to vary the color in ramps until you find a setting that produces acceptable quality.

4:1:1 means that four times the subcarrier frequency (4.43 Mhtz) is used to define the luminance channel information, and one times the subcarrier is used to define the two color channels. Some variants of DV video will also have 4:2:0 signal structure, which means 4 times subcarrier for the luminance channel, and 2 times subcarrier for the combined chroma channel. 4:1:1 is usually quite acceptable for most video applications, but may not be very suitable for compositing or special effects requirements- especially chroma keying.

DV signals are carried down a digital cable or link between devices, either in a 4 pin or 6 pin configurations. Most applications for DV links are between computers and camcorders, but some limited DV-capable production switchers have been available on the marketplace. These switchers are somewhat limited, providing 2 or 4 DV inputs. Some of these lower cost production switchers are not recommended for professional applications that some ministries may require because the durability and reliability of the products may fall short of your expectations. Depending on your requirement, a couple of offerings in the market place may provide reasonable quality and operations for your ministry. As with any major equipment purchase, talk to other ministries or customers using these products. A hands on demo may be advantageous to assure you the switcher is going to provide the results you require.

Overall the quality provided by DV tools is quite impressive, especially when considering the relatively small investments required for these devices. Some limitations do exist in installing them though, specifically longer distance cables. While DV cables are available up to 164 feet long, these will not be able to provide power at these distances and are somewhat expensive. Do keep in mind that the signal was originally designed for camera to computer or camera to camera applications, so the tools available for your media ministry may not be available because they simply may not exist.

The next level is component digital; also know as Serial Digital interface, SDI, CCIR-601, 601, or Digital Betacam. This is the highest quality signal available in standard definition television. Think of component digital as a digitized version of component analog. The signal is literally 0’s and 1’s, can be in 8 bit or 10 bit resolution and can also include embedded digital audio. The signal is carried down one precision video cable, with 75 ohm video connectors.

The significance of 8 bit vs. 10 bit resolution can easily be seen in gradient backgrounds, 8 bit images can have the stair stepping we talked about in DV. The same image represented with a 10 bit signal will be virtually immune to this stair-stepping effect.

Another significant quality improvement is that the signal is 4:2:2, with double the chroma resolution. This makes 10 bit component digital ideally suitable for special effects, graphics and compositing work.

The cost for component digital is the highest for standard definition, but is certainly the best investment for quality, short of High Definition video. When installing a serial digital system I highly recommend that the installer utilize high quality cables and connectors that are specifically capable of digital signals. If they are high quality they will also work with HDTV equipment if you should ever upgrade in the future. The most expensive part of installing a system is the installation labor for the cables, not the cables themselves. The cost difference between adequate cabling and connectors and high quality cable and connectors is pennies per foot or connector- the labor is far more expensive.

Numerous issues are very important in regards to cable selection and installation methods. Future articles will discuss these issues to greater detail, as we do not have enough time to cover this issues adequately now. For now though I want to stress the importance of selecting a vendor who is very familiar with video systems and the proper installation of them. If your installer is not familiar with these issues or only is experienced in other cable or equipment applications (electrical, data, and sound for example), I recommend you find an installer who is experienced in installing broadcast video systems.

In a nutshell, we have covered the major standard definition systems that are currently available. Future articles will discuss High Definition systems, the formats, components and creative issues that these exciting formats bring to the table.

What are the deciding factors in selecting the right format for you? Quality expectations, purposes for system, length of time you intend to use the system in that space and existing staffing are just some of the important factors. What are your ministry goals in both the short term and long term? Do you intend on ever broadcasting? What are your special effects requirements during a service? How many inputs will your production switcher require? What kind of technical and creative capabilities do your staff and volunteers have? Is your main goal IMAG or distribution of services on video tape or DVD’s?

Then the all-important issue of budget must be determined. You may want to delay your system purchase if you have a limited budget and your goals are more than your budget provides. Sometimes it may appear that investing in lesser equipment for short-term goals is an appropriate decision, but ask yourself the impact those decisions will have on the person actually viewing the video. The output of your system is a direct representation of your ministry. You may want to work with staff members and volunteers to build their skills and wait to implement the equipment that fits with your quality requirements and will reflect the long term ideals of your media ministry. In the end this approach generally provides better justification for future budget planning.

These are certainly some important issues to discover that will help you decide on the proper format for your ministry. I do suggest that if you are not comfortable in making these decisions, do hire a knowledgeable professional with broadcast experience to help guide you- as the investments you will be making are significant.