WebTV and Images

WebTV is big and it's going to get bigger. For a few hundred bucks allot more people will be using the web. This is fact and we must live with it. WebTV is different than most computer systems. The first difference is the limited capability of the computer and browser. At the time of this writing WebTV can't handle Java Scripts, Frames, Animated GIFs etc. The computer limitations will no doubt lessen. The main concern for people making web images is the display device, the TV. It isn't a computer monitor. A TV tube doesn't have the resolution of a monitor and TVs are interlaced. These problems impact images more than text. The size of text can be increased at will by the browser so it can be easily read. Not so with images.

Resolution

      The resolution of the population of TVs in use varies considerably. We must consider that most people who buy a WebTV will have a reasonably good TV. Even reasonably good TVs are no match for a computer monitor. The way a TV encodes the signal is a throwback to the old days of black and white TV. The intensity is the predominate signal. When color TV came out the color information for the three colors (RGB) was crunched into the signal on a sub carrier. This is what most TVs use (NTSC). A better standard, that very good TVs have, is SVideo. SVideo uses two separate signals. One for intensity and one for color. But all three colors are still crunched into one signal. This isn't nearly as nice as having a separate signal for each color. The picture from a WebTV box will be better than what is received from a cable or antenna. It's the same quality that is received from a digital satellite dish.

     The result is a smearing of one color into an adjacent color. This is called color bleed. Look at the vertical color bar's on your TV. Notice the bleeding between colors. High contrasting colors that are adjacent to one another across the screen will bleed together.

     The colors smear more when there is a small change in luminosity with a large change in color. For example when one of the colors is turned on full say blue, which is 0,0,255, to red, which is 255,0,0. The change in luminosity between these two colors is zero while the change in color is high.

Interlace

     The second problem is TV tubes are interlaced. The vast majority of people can't see the flicker from a light, flashing faster than 50 or 60 times a second. The vast majority of people can see the flicker at 30 times a second. In days of old when bandwidth was very limited, designers wanted to put up the largest picture possible, fast enough to keep it from flickering. They discovered that you can update every other line on a TV, 30 times a second and the flicker can't be seen easily. The only time that the flicker can be seem is on high contrast horizontal lines. It is called buzz. It happens when one line across the screen is a high contrast from the next line on the screen. Because individual lines only get updated 30 times a second, a horizontal buzz line can be seen. Buzzing also occurs when a horizontal line pattern lines up with the lines on the TV.

     People making video graphics for the TV are very concerned with buzz. You can see buzz on regular TV graphics when designers get sloppy. Now everyone producing web pages must be concerned with buzz.

     WebTV has and will improve filters that attempt to reduce the impact of the TV display device. These filters dither high contrast horizontal lines. They also reduce the impact of bleed. They arn't perfect and can change the appearance of the resulting image. It's best to consider the TV output when making the image. If you are interested in the WebTV boxes. Go to Magnavox Which has a nice technical section. Or Sony. They both have WebTV boxes If you want to see what's going on in the WebTV world, go to webtv.com.

What To Watchout For

     The first thing is text. The size of normal text can easily be increased but the size of text in an image can't. All those buttons that have very small text in them are hard to read. For example the Bob's Home button at the bottom of the page. This is hard to read on a WebTV.

     Another potential problem is color scheme and layout. It's nice to chose colors that don't bleed easily and few high contrast horizontal lines to start with.

     Link boarders on images can buzz just like a horizontal line. High contrast between the horizontal edges of images and the background can cause buzz. This is reduced by filters but not completely eleminated.

Should You Fix It

     More importantly, should you tell your customers. It depends on you, your customer, the web page and how bad the problem is. A picky person would buy a WebTV, check all the pages and update everything that has a problem. Good Luck. In the real world, there are to many images.

     If your customer will be willing to pay to update any images that have a problem, it's work. If you don't have the time give it to me. If the web page is something that will be browsed by WebTV allot you should update it. If it won't be browsed by WebTV, don't worry about it.

     If the problem is gross you should fix it. If a TV browser can't get around because the navigation buttons can't be read, you should fix it. If the buzz gives you a headache while watching it, you should fix it. If it's just some minor bleeding or light buzz people watching TV are accustom to it.

How To Fix It

Pick a good color scheme and layout for WebTV.
WebTV dosn't like all white backgrounds like this page.
Make all text large enough to be read on a medium quality TV.
AntiAlais all text. This is blurring the text, normally for one pixel.
Blur the horizontal edges any high contrast horizontal line or box.
Don't make patterns that inherently buzz.
Use a guard band or gap around objects to keep them from bleeding. This is usually a black outline.
Watch allot of commercials on TV and see how the professionals do it.

Sorry this is so boring. Naked, about images without images. You can't really simulate the effects of TV without TV.