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Attack of the Killer Subtitles
By Adam Schenker
I'm not an expert in video signal theory or anything like that. This article is just a brief (well, it was supposed to be when I started), general overview compiled from various sources for your information. I don't make any claims about the accuracy of the information here, but most of it seems to be verified by multiple sources. I'm not responsible if you decide to spend $1200 on a new TV to read better subtitles and things get worse. I'm still stuck with my old set and have not yet personally evaluated better TVs to see if they do indeed fix the problems described. Good enough? Ok, let's get to it...
The purpose of this article is to explain why some people are having problems with the appearance of subtitles on certain anime DVDs. I'm not going to try an explain every possible problem, only those that seem the most likely. I'm also not going to go into a lot of technical detail about things like scan lines or signal frequency characteristics. I'm just going to give a quick overview about why certain problems happen with subtitles, what they look like, and what you can do to try and cope with them. So without further ado, here we go.
A tale of two signals
The majority of televisions in the U.S. have 2 types of video input connections: RF, which is the coaxial cable used to hook up a cable TV signal, and composite, which is the yellow RCA jack for connecting to devices such as VCRs, camcorders, DVD players, video game consoles, and so forth. The video signal that travels along these cables and into your TV is actually two different signals which are intermingled into one. The first signal is called luminance, which is the black and white (brightness) information. The luminance signal is usually referred to as Y. The second signal is called chrominance and it has the color information. Chrominance is usually called C.
When the combined signal arrives at your TV, it's up to some circuitry in your TV to break the signal into its Y (brightness) and C (color) parts. A wide array of different hardware and techniques is used to do this (some of which I'll cover in a bit), but every TV has to do it somehow in order to create the picture. The problem is that many TVs, especially low-end models, don't do as good a job as they could at separating the Y and C signals. Sometimes part of the signals may be lost or a piece of one signal may not separated out and contaminate the other. When this happens you get visible artifacts on your screen.
Don't cross me
There are two major artifacts that occur due to poor Y / C signal separation. The first happens when some of the Y (brightness) signal is left in the C (color) and is called cross-color. Cross-color manifests itself as rainbow swirl patterns wherever there are closely spaced or fine vertical lines. As you might expect, subtitles are prone to this problem, especially letters like a lower case "m" or lower case "l" with their thin vertical strokes. On my system, most of Pioneer's subtitles (the second one they used with the thicker black border) have this rather obvious problem. It's also visible sometimes at the end credits of a movie with thin white lettering against a black background. Cross-color isn't as evident on non-vertical lines. For example, on Pioneer's subs that I mentioned above, when they switch to an italic style (like when a character is thinking) the effect almost disappears.
The other problem happens when some of the C (color) signal is left over in the Y (luminance). You guessed it, this is called cross-luminance. However, it's probably more commonly called dot crawl. Dot crawl occurs when two contrasting colors are horizontally adjacent to each other. At the edge where the colors meet you can see a pattern of moving dots or sometimes just a stationary pattern. From farther away it can make parts of the picture appear to sort of shimmer in contrast to other places in the picture. A good example of this is the main menu of the Sailor Moon S Movie DVD. Look at the red bow to the left of Usagi at her waistline. Look closely at the vertical left edge of the bow and your should be able to see dot crawl if your TV doesn't handle the Y / C separation correctly. Subtitles are also prone to this problem because they tend to be bright colors which contrast with the colors of either the surrounding border or the picture.
Y, C and U
If you don't see the problems I described above, consider yourself lucky since you own a good TV. For the rest of us who do have the problems, what can we do? The news isn't too good I'm afraid. If you have a cross-color problem, you can try reducing your TV's color setting until the effect is reduced to your liking. Of course if you turn your color all the way down to 0, you in effect eliminate the C signal all together and the problem should vanish. However, if you do that you'll get a black and white picture. Not a great solution in my opinion. Eliminating dot crawl is trickier. Reducing your sharpness and color settings might help a little, but there doesn't really seem to be much you can do.
The best (and really only) solution that I've found seems to be to purchase a TV that reduces or eliminates these effects. Many mid-range and above sets have special circuitry called comb filters which does a much better job of separating the Y and C signals correctly than those found in low-end sets (which seem to be mostly simple analog filters). Comb filters come in many varieties, from the simple 2-line analog type, to the most expensive digital 3D filter which is motion adaptive. Generally the higher end TVs have the best comb filters since they can be expensive. While they may not eliminate every artifact and may introduce a few subtle ones of their own, even low-end comb filters should improve over the case of having no comb filter at all. You can buy external comb filters, but they tend to be very expensive (as much as a new TV) and output either S-Video or component. So if you only have composite or RF on your existing TV, they won't help anyway.
Your first reaction upon hearing this may be to start looking at comb filter specs on TVs you're considering buying. However, there is an even better solution than comb filters for DVDs. On the DVD itself, the information encoded digitally about the picture, the Y and C signals, is already separate. Most, if not all, DVD players can output a video signal format called S-Video. This format uses a 4-pin connector, like you might see used for computer peripherals, where the Y and C signals are transmitted completely separate (in fact S-Video is sometimes called Y/C video). If you have a TV with an S-Video input, there is no need to do Y / C separation in the TV because the signals are already distinct. No Y / C separation, no cross-color or cross-luminance! Even better is another format called component video, which uses 3 video signals. However not all DVD players output component video and at this time it is not as common for TVs to have component inputs as S-video.
To sum up, if you're having problems with your anime DVD subtitles because of the problems described in this article (or just Y / C separation in general) and it's a major issue for you, you'll probably want to start looking into getting a new TV set with at least S-Video input (a larger screen would probably also help subtitle readability if you can afford it). If you do decide to shop for a new set and have a local store that's willing to help you, take a couple of problem discs with you to try out so you can see if you're getting the improvements you want.
For more information
Here are some pages to visit for some more technical details about Y / C separation issues: