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What
Happened to My Colors!?! What About PAL
and HDTV? PAL was designed in 1967, fourteen years after NTSC, and was not backwards compatible with the previous monochrome format. That gives PAL a few advantages over NTSC. However, it had to deal with the same physical bandwidth limitations that restrict NTSC so PAL still has quirks and limitations. PAL uses the YUV color space rather than YIQ and it supports the full range, so that over-saturated colors are not a problem. PAL also has more bandwidth devoted to the composite signal, allowing higher horizontal resolution, and has 625 lines instead of the 525 lines of NTSC. On the downside, PAL has a lower refresh rate of 50 Hz interlaced, which makes flickering worse. The color-encoding scheme used by PAL works best if the color information from adjacent lines is blurred together by the TV, thus, lowering vertical color resolution. PAL's greatest advantage is probably the great number of TVs that have high quality SCART connections, allowing all of the problems except for interlaced flicker to be avoided when playing video games. HDTV is great. At the lowest resolution of 720x480, you actually get to virtually see all of those pixels. In addition, the 720x480 resolution is a progressive scan resolution with no interlaced flicker. HDTV's are rare now, but the new generation of consoles just might be the killer app to push consumers to get them. If things had worked out differently, we could have had a radically different set of TV problems. In 1950, the FCC approved a color television system designed by CBS, with the first broadcast happening June 25, 1951. However, virtually nobody saw it because only a few dozen of the twelve million television sets in America could receive color. The CBS standard was designed to work with TVs featuring a spinning filter wheel. One hundred and forty-four fields per second were broadcast displaying red, green, and blue sequentially. Thus a complete field could be displayed 48 times a second, and a complete frame 24 times a second (Reitan 97). If the CBS
standard hadn't died then we would have a television standard that was
much more compatible with film - it has the same frame rate. It would
have avoided the high-pitched 15KHz hum of NTSC. However, we would have
had a pair of spinning wheels inside our TVs rotating at 1440 rpm. Finally,
we would have just had 405 vertical lines instead of 525. It Doesn't Have
to be This Way Many of the limitations of NTSC come from the need to transmit a backwards-compatible signal through the air (or through conventional cable with the frequency limitations being the same). However, there are an increasing number of consumers who aren't using their TVs in this way. If you are playing console video games, web browsing on your TV, or watching digital cable or digital satellite TV then there is an RGB frame buffer located less than ten feet from your TV. Why on earth are we squeezing that perfect RGB frame buffer into an archaic 6MHz signal so that we can carry it across our living room! S-Video is a big step towards avoiding the pointless encoding and decoding by keeping the luminance and chrominance signals separate. However, even S-Video is still limiting the bandwidth of the I and Q signals. If console
video games, digital cable boxes, and digital satellite boxes had RGB
output jacks and if TVs started more commonly having RGB input, then most
of these problems, excluding interlaced flicker, would go away. There
have been many reasons to support direct RGB connections in the living
room for a number of years now, but a lack of consumer demand or a lack
of industry support has left us with composite connections as the standard. What Can Game Players
do About These Problems? As a consumer, there are quite a few things you can do to improve the video game images and other graphics displayed on your TV. The basic trick is to avoid putting too many signals on a single wire. An RF connection to your TV is the worst. RF means that Y, I and Q are combined with the sound channel on a single wire, and there are many ways they can interfere with each other. The next best thing is a composite connection, which at least keeps the sound separate. S-Video keeps Y and C separate, thus avoiding chroma crawl and allowing the Y signal to have higher frequencies. Since separating Y and C is the hardest task for a TV, S-Video produces the largest jump in video quality. Finally,
component video such as YUV or RGB keeps each signal on a separate wire
and should allow the full resolution to be displayed. What Can Game Authors
do About These Problems? Fancy connectors are great for your own personal setup, but don't make the mistake of assuming that your customers will be plugging an RGB connector into their home theatre. The most common connection in North America is composite so be sure to test your game with it. Sophisticated RGB encoders can insulate you from some of the problems of NTSC, but they won't let you exceed its fundamental limitations. Avoid thin horizontal lines. Horizontal lines typically cause flickering. If there is a vertical filtering option, use it. Doing this properly requires that you render a full frame, even if you are running at 60hz. Menu screens with too much detail frequently cause the worst flickering. They are also the easiest to fix, since you are explicitly creating each pixel. Making full use of the available resolution means creating detail that has a fractional pixel width. Use low contrast lines to simulate thin lines, and use antialiased fonts to allow greater detail. If you find that your graphics are displaying poorly then write a tool to filter your screen shots appropriately in Y, I and Q to see how much you are exceeding the limits. Refer to my web site for sample codes. If necessary, you can pre-filter your texture maps. Remember that brightness-detail smaller than one and a half pixels wide can't be displayed, and color-detail smaller than five pixels wide will also be filtered out. Check for
illegal colors. Don't just test on one TV - and certainly don't just test on one really expensive TV with a comb filter or an S-Video connector. This will give you an inaccurate view of what your game will look like to most people. Test on what your target market uses. It can make a big difference. References Conexant,
Adaptive
Flicker Filter, Video Encoder, CX25870/871 - 100431_pb.pdf Jack, Keith, Video Demystified, Second Edition, LLH Technology Publishing Martindale, David and Paeth, Alan W., "Television Color Encoding and "Hot" Broadcast Colors", Graphics Gems II, Academic Press, Inc., 147-158 Poynton, Charles, Gamma FAQ Reitan, Ed, CBS Field Sequential Color System Schmandt, Christopher, "Color Text Display in Video Media", Color and the Computer, Academic Press, Inc. Taylor,
Jim, DVD Demystified, Second Edition, McGraw Hill ______________________________________________________ Discuss this article in Gamasutra's discussion forum.  [Back
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