Attaining the NTSC Television System Potential — Part 1: Expectations

Home | Audio Magazine | Stereo Review magazine | Good Sound | Troubleshooting

A lot of information about producing good television pictures has been scattered among the many articles assembled for Widescreen Review since 1993. It seems appropriate to organize them into a series of articles that would take you step by step through the process of getting the best possible picture in your home. What’s important? What needs to be covered?

As we have emphasized over and over again, the idea of television is that it is a tool for communications. It is a means by which ideas and sometimes even entertainment can be conveyed to an audience. In describing the visual side of the medium, we’ve discussed the importance of accurately reproducing the image. As human beings, we acquire much of our knowledge from the visual domain. Children learn to crawl, walk and talk because they see things that they want. Yet few of us know enough about our visual sense to judge picture quality, good or bad. We take a lot far granted in the visual world and all too easily accept poor quality.

As with any form of communication, there is a limit to the performance capability of the transmission path. I believe that a major part of our accepting any particular level of quality is based on expectation. A parallel can be drawn from the path that the audio industry has traversed. There were the early days of micro phones that could pick up some semblance of sound, amplifiers that could sort of convey the information, and speakers that could move air. The reproduced sound didn’t come close to the source audio in quality. Yet in the early days of the Edison phonograph major vocal stars pronounced the system as being transparent.

Today, we all know better. We are christening the current generation of digital audio as being just like the real event. Any communication link is more like a funnel, a path that limits what comes out at the other end. The narrow part of the funnel has been getting wider as technology improves. With each major improvement, the difference is often large enough for many of us to say of the current generation, “this is it, the ultimate in quality.” In reality, it’s the ultimate until the next widening of the funnel.

A Frame of Reference

This frame of reference has two sides. In the visual communication world there is 48 frame IMAX or the 60 frame, 65mm taking format called Showscan as a reference. For any of you who are still new to Showscan, the image has a significant three dimensional quality to it. Not because there is anything 3-D in the format, but because it contains so much more motion and detail information than anything you’ve seen before from a regular film format that you think it must be 3-D. You might be tempted to say that Showscan is the limit of visual communication.

Not compared to reality it isn’t. Yet seeing Showscan, knowing it’s capabilities, you still willingly go back to poor quality movie theatres or worse yet to television. Why is it so easy to step backwards? Is it possible that if you saw much more of Showscan, you would be less likely to accept 35mm formats?

Think about the transition from AM radio sound quality to FM. At least in my world, there was no going back. To this day, I’m no longer able to “DX” on the AM band, just as I’m no longer able to sort out individual conversations in a room full of talking people. When I go flying with friends, or try listening to aircraft communications on channel 9 of commercial flights, the fidelity is so poor that I can’t understand the majority of what’s going on. Having lived with high quality FM as a reference, I can no longer sort out the information from the associated garbage of lesser quality audio systems.

In the electronic visual world, I’ve been spoiled by the capability of our 525 line system, relative to the poor interpretation many of you have watched at home. I’ve seen the light—and there is no going back—to the point of my trying to show a large audience what they’ve been missing. When a picture is bad, I know how and why it is bad, and what needs to be done to fix it. Before you jump on me about the coming of HDTV, its ability to look much better than our 525 line system is dependent on expensive well calibrated display devices. The investment required to make it look a lot better than our current system is significant. I believe we should all first spend our efforts catching up to our current capability. Once there, we can more accurately judge the cost versus quality improvement of any new system. While on the subject of cost, moving us all towards the capability of our current medium will help bring down the cost of any future system. If you decide to venture into HDTV with a display device truly cap able of reproducing the format, the right processing for component 525 line pictures will make them look better than ever.

There are parts of our current television delivery system [as of this writing, ca. 1998], such as LaserDiscs and DVDs, which provide a signal quality that begs to be properly reproduced. DVD or MPEG-2 encoded DSS should reach a quality level way beyond what most of us can reproduce in our homes. The addition of video processing in the form of scaling will add the long life needed to engineer real advances in image quality. The consumer should be spending time taking advantage of what’s currently available rather than worrying about some other signal taking its place. In doing so, we’ll also meet the challenge of other currently available high quality mediums such as computer graphics.

A Video Standard

My attempts at showing a larger audience what they’ve been missing in NTSC picture quality got started with A Video Standard. While I initially thought it would be the pinnacle of my communicating with you, it has turned out to be just the starting point, the foundation for things to come. Through the Imaging Science Foundation (ISF), put together by Joel Silver and I, we now teach home installation people how to get good pictures for their clients. I’ve long known that the ISF training effort is only half of the education process. You, the consumer of visual information, has to know that there is a better way to view the electronic pictures coming your way.

That’s where this series of articles comes into play. There is a lot of what I teach installers that you should know. We are a long way from the product being so good that the consumer doesn’t need to care; there are even manufacturers that are convinced that you wouldn’t like a good picture if you saw one. That’s self-fulfilling, they don’t include the capability of properly reproducing the incoming signal. If you don’t have the opportunity to see a good picture, how do you know what you’re missing? It’s a lack of education on the part of the consumer that has allowed manufacturers to get away with the terrible products they put in front of you.

There is no substitute for long term expo to good pictures. It might also be accompanied with an understanding of what makes a particular image look good. Once you know the difference, there is no going back to the poor quality pictures you’ve probably been watching. Yes, I’m out to spoil you. I want enough of you to recognize the common short-comings of mass display technology to demand better. In many cases, knowing what you should or should not expect of a display device will help reduce the cost of the device while delivering far better quality.

Television is a means of mass communications. As such, it has a set of rules, a language that defines its operation and capabilities. If we are to take advantage of what it has to offer we need to know a bit about its language.

Since showing you good electronic pictures in this publication is difficult, what I’d like to do is put you through one of our ISF courses. We’ll describe what you should be seeing at home, what you should expect from a display device, and what it will take to obtain and maintain it.

The premise of the course is that the television system is a canvas. An artist creates an image in a well defined system. The information is conveyed to you through a highly specified funnel. It comes out on coaxial wire in your home. You have to do something with that signal to see the intentions of the artist. At minimum, you should first have the ability to repro duce it correctly. That should be the starting point of any display device.

As much as I believe just living up to the potential of our current system is a significant challenge, we might also keep other technologies, such as computer graphics or HDTV, in mind.

There is a lot in common among them. In the not too distant future, computer graphics will be your introduction to high definition images.

We’ve begun with a description of our philosophy, an indication of where we are coming from. If what we’re about were summarized it might go something like this.

Television is a means of mass communications. As such, it has a set of rules, a language that defines its operation and capabilities. If we are to take advantage of what it has to offer we need to know a bit about its language.

How much do you personally have to know? If the system creators are doing their job properly, you shouldn’t need to know anything more than how to operate it. It’s like driving a car. In my case, I initially had to know a lot about them to keep my first few on the road. Now that I am able to acquire new cars, it’s become automatic, the dealer takes care of technical parts. I no longer keep track of four overhead valves per cylinder or fuel injection. I just enjoy the trouble-free ride.

The thought of being able to do that in the world of television, just enjoy the ride, has been with us since the first days of color TV. We’ve always been told to trust the manufacturers and dealers. Well, I’m here to tell you that most of them lost sight of the system rules somewhere in the mid-1970s.

The start of the NTSC color system was actually pretty good considering that it took more than 10 years to get from definition to implementation by all three networks in prime time. In the early days, color TVs were installed by factory trained dealers.

That stopped in most markets by the late 1960s. That’s the point where we as consumers needed to learn the language of the system. Most of us today will still require the assistance of trained technical people, with their instrumentation, to get the video system up and running properly. Yes, the days of having someone come into your home and set up the TV set needs to come back. Just as in the automobile industry, we all need to be able to recognize when the job’s been done right, or we’re going to continue to be an easy target for a bill of goods.

We’re going to request your active participation in making adjustments. We’ll detail procedures you need to know in order to properly run your TV the same size. Toggle back and forth between the two. Are they being reproduced at the exact same size? It’s likely that the brighter Window pattern is being reproduced larger in size than the lower level Window pattern. If there is even a hint that the size of the high level Window might be larger than the low level Window then the light output from your set is turned up higher than it should be. Now that you have an idea of what you’re looking for, let’s try spotting a similar situation in a single test pattern.

Select the PLUGE with Log Gray Scale pattern from the same areas of the disc where you found the Window patterns. On the right side of the picture you’ll spot some gray rectangles, the top of which is actually 100 percent white, just as the bright Window. Look carefully at the size of this with respect to the ones below it. It’s likely that the top rectangle is larger in size than any of the ones below it. If the light output is grossly higher than it should be, the second rectangle will be larger than the third down from the top. Keep in mind that in the incoming signal, the size of all of the rectangles are the same. If the peak white level of the set is turned down, you should be able to reach a point where all of the rectangles will be the same size. In this condition your set is beginning to more accurately reproduce the incoming signal.

How do you turn down the peak white level of the picture? As we mentioned earlier, the Contrast or Picture control is used to set the level of peak white on most sets. Try turning it down to the point where the top rectangle is no larger in size than the ones below it. We aren’t finished yet, it may have to go lower still. It turns out that adjusting the Contrast control down often pushes picture black level far below its correct setting. Raising black level back to where it belongs will also raise picture white level, which will again have to be turned down.

The next step is to properly set the level of black in the picture. For the time being, we are going to stick with the same test pattern, the PLUGE with Log Gray Scale. We’ll complete the discussion of properly setting black once we get beyond determining the peak white capability. Once you’ve turned the Contrast or Picture control down to the point where the rectangles are equal in size, the test information on the left side of the picture, the PLUGE, has probably disappeared.

In terms of displayed light, black is defined as an absence of light. Anything in the video signal that is at black or below black should not be displayed on your picture. What you see as black is dependent on the amount of ambient light hitting the surface of the picture. If there is a lot of light on the set, black level will have to be set higher than on a set with no ambient light reaching the picture surface.

We already know that there is a peak limit to the light output from the set when the video signal is at 100 percent white. What do you suppose happens to the contrast of the picture if black has to be set high to overcome ambient light hitting the set? Yes, the contrast range is reduced.

In properly adjusting black level, start by turning up the Brightness or Black Level control to the point where you can see two vertical stripes on a gray back ground from the full field PLUGE test pattern. The left vertical stripe will be darker than the background and the right vertical stripe will be lighter than the background. In this test signal, the background is at a voltage level in the video signal defined as picture black. In other words, that back ground should not produce any light from your set. It’s black. So how will this test pattern help us properly set the level of black on our set?

The left stripe is actually below video black. That’s allowed in our video system. There is often information below black that is not intended to be seen. Reducing the Brightness or Black Level control on your set will first bring the blacker than black stripe to a point of absence of light. Further reducing the Brightness control will bring the background to a point where it just matches the absence of light in the position of the blacker than black stripe. That is the correct setting for black, the point where blacker than black and black just match in level. It is important that the lighter than black stripe still be visible.

At this setting of the Brightness control, any information in the video signal at or below black won’t be reproduced. Any information above black will be seen in the picture. There are qualifiers on setting black. We’ll get to those once completing the discussion of maximum light output capability.


Above: High And Low Level Window Patterns

Now that black level has been set, go back and check the peak white level. Chances are that it is now higher and the rectangles are no longer the same size. Turn the Contrast control down as needed. This may again change black level, so look at the left side of the picture and adjust the Brightness control if necessary. Check Contrast once again and adjust if necessary. At this point we’ve reached the point of discussing fine tuning of the Contrast control, most likely taking it down even further.

You’ll have to move up close to the set for this next part. While still displaying the PLUGE with Log Gray Scale, look at the size of the line structure in the top rectangle on the right side of the picture. Compare it with the size of the line structure in the rectangle just below it. Are the lines in the top rectangle thicker than the lines in the rectangle below the top? Can you even see the line structure in the top rectangle?

They should be approximately the same size if information at all levels of gray are to be accurately reproduced. If the line structure is noticeably thicker on the top rectangle, further reduce the Contrast or Picture control until the lines in both rectangles are the same size. We have now reached the correct setting for Contrast. Anything higher will distort the way the incoming signal is reproduced. We won’t have a good picture with higher levels of contrast.

Search for real picture material on the disc. How bright is the picture? Did anyone come up with “rather dim” for an answer? The results I got on my set at home were rather startling. As my 27- inch set came from the factory, it was producing 187 foot-Lamberts. Once the Contrast was reset for a good picture, peak light output was reduced to less than 30 foot-Lamberts. That’s a reduction of 84 percent from the factory preset. In my case, ambient light has to be tightly controlled in order to watch a good picture.

Are there any other issues with high contrast levels, other than not accurately reproducing the picture? Some of you know me well enough to know that I wouldn’t raise that question if there weren’t some important issues to discuss. In the case of my set, leaving the PLUGE with Log Gray Scale on screen any longer than thirty seconds at the factory reset position will start to damage the tube. The top rectangle will start to turn brown. If I quickly change the pattern, you’ll see a residual spot the size of that rectangle in the new image. It will take much longer than thirty seconds for that to go away. Think what might happen if I were watching CNN, with its white logo in the lower right corner, all day long. When I eventually changed channels, it would still say CNN in that bottom corner.

Many manufacturers will warn you to turn the Contrast control down if you are playing video games on your TV set. The fixed boarders of the game can burn the set, just as the CNN logo will remain in the picture.

When Contrast is up higher than it should be, the effect on the image being reproduced at a larger size than dictated by the video signal is called “blooming.” There are phosphors inside the tube that produce the light. They can only take so much energy. If more is delivered, by turning the Contrast up to high, it will be dispersed to adjacent areas. A larger area will therefore be lit up than was intended by the video signal.

What caused the white rectangle to turn brown on my set? It turns out that there is a shadow mask behind the phosphor set. (This is shown in diagrams on each disc.) It absorbed much of the beam energy, heating the metal in the process. With such high contrast levels, the metal starts to change shape, warp. If the beam current energy is quickly reduced the damage shouldn’t be permanent. Then again, if it isn’t reduced, count on problems. Please don’t forget that the energy that is making it through to the phosphors is more than they can take. You aren’t doing them any good either.

In summary, high contrast levels create blooming, which translates into poor picture quality. It can also translate into poor picture life.

Now back to the real picture information. Black level may or may not be correct on all of these images. It’s time to look at the qualifier on properly setting the level of black. Many set manufacturers have decided that you are going to be watching television in high ambient light conditions. In an attempt to accommodate, they don’t make an effort to hold black at black independent of picture content. It turns out that if they leave a few pennies worth of parts out of the set that black level will float in a direction they consider good. What does that mean?

If the average picture level (APL) is high, black level will be low. If the APL goes down, say as in a night scene, black level will float up, making it easier to see details in the background when there is a lot of ambient light hitting the set. While that may initially sound like a good idea, and it is in high ambient conditions, dark scenes will always look washed out.

Worse yet, the contrast of the picture is always changing. That isn’t at all desirable where good picture quality is the goal.

How do you determine if your set is holding black at black, independent of picture content? We need a couple of test patterns, each with a PLUGE signal in it to see what your set is doing with black level. One of the test patterns will have a high APL and the other will have a low APL. Actually you have already been working with the low APL signal in the PLUGE with Log Gray Scale. Search for the high APL PLUGE Pattern. In this signal, the entire right side of the picture is at a 100 percent level, a high average picture level. Set black the same way you did before, this time while displaying the high APL signal. Set the Brightness or Black Level control so that the blacker than black stripe and black background just match in level, with the lighter than black stripe still being visible. Now switch to the PLUGE with Log Gray Scale. Is the PLUGE still displayed properly? If your set is good at holding black at black, it will remain correct. If the set is poor at holding black at black, the blacker than black stripe will be clearly visible on a gray background.

By the way, while I think of it, both of these patterns are black and white in their signal source. In referring to the background as gray, it should be gray, not red, green, blue or some other color. If it’s not gray, that’s another problem, one you’ll have to seek qualified help to fix. That’s where the ISF-trained person will help.

If your set is not holding black at black, independent of picture content, you’ll have to use a high APL test pattern containing PLUGE to set a useful level of black. There is usually no easy fix for such a condition. It requires circuit modification. The SMPTE Color Bar Pattern qualifies as a high APL test pattern. If your set is good at holding black at black, continue to use the PLUGE pattern with the Log Gray scale. It is much easier and more accurate than using the PLUGE in the SMPTE Color Bar Pattern.

Now that you know the limit of your set’s ability to produce a bright picture, what are the advantages of operating at such low light output levels? You’ve hopefully already figured out that the amount of detail in the picture will go way up with this new, lower light output setting. There are other advantages, such as the possibility of better color fidelity, if all of the other controls are set properly. Depending on the type of display device, life expectancy can be greatly extended by not overdriving the set. Front and rear screen projectors, in particular, fall into that category.

Now that you see the real light output capability of your set, you’ll better understand why ambient light has to be tightly controlled. We have yet to discuss one more parameter in setting the maximum level of contrast, which is the capability of the high voltage power supply to track the peak light output capability. That will be the starting point for the next section. We’ll go into decoding the color information from the NTSC signal from there. Included will be calibrating the Color and Tint controls. We’ll finish with the Sharpness control.

The color section will serve as the introduction to the NTSC color system. In the third part we’ll talk about the signal itself, its origins, how it’s put together and how we take it back apart. S-Video will be included in that section.

In the meantime, adjust your ambient lighting to accommodate the new lower setting of the Contrast control and enjoy a lot more picture detail. In preparation for the next section, turn the Sharpness control way down as well. We’ll explain why then, but wouldn’t want you to miss out now.

[Adapted from Widescreen Review--Imaging Science Theatre 2000 (1998)]

Next | Prev.

Top of Page   All Related Articles    Home

Updated: Wednesday, 2016-09-21 13:40 PST