Designing Custom DVD Menus: Part II

DVDmenuIn Part I, we discussed some of the basics for designing DVD menus. In Part II, we’ll expand on these basics and by discussing some of the rules and tips that will help you create professional DVD menus.

Before the advent of desktop editing, graphics were created on specialized equipment specifically designed for video production. With the advances in video editing applications for the PC, you’re going to create all of your graphics on a computer. This presents a problem because applications like Photoshop weren’t designed to create graphics for video.

When designing menus on a computer, they’re going to look great, but put that menu on a TV, and you may find it doesn’t look quite the same. Why is that? TVs and computer monitors display graphics in a completely different way. To help avoid these problems, it’s necessary to understand how they differ and what you can do help prevent these issues.

Terminology
Let’s take a minute to explain a few key terms. When talking about graphics not displaying correctly on TVs, we refer to artifacts or artifacting. Artifacts, as they apply to DVD menus, are distortions or errors created during compression, during the process of building the DVD (mixing), or created by the interlaced scanning process. Essentially, artifacts are any visual distortions not desirous in the image.

The terms used to describe artifacts (distortions) are Twitter, Buzzing, Mosquitoing, and Crawl. These terms all apply in general to artifacts on a TV but there are subtle differences. Twitter refers to a flickering that happens to a thin horizontal line. The line actually appears and then disappears in a cycle creating a flicker. Buzzing originally referred to the audible buzzing noise created in a TV signal when white levels were above the NTSC limits or “too hot.” It now refers to the edges of a graphic or font that appear to shimmer, glow, or move – also referred to as Mosquitoing. Crawl is when part of an image appears to move or crawl across the screen.

These artifacts are difficult to explain so it’s best to look at menus to see for yourself. Start looking at DVD menus, even professional ones, and you’ll see plenty of examples of artifacting. Look at what works and what doesn’t. See if you can determine patterns. Are there particular fonts, colors, or designs that work or don’t work? As you start to look closely at professional DVD menus, you’ll start to notice that artifacting many times is unavoidable. Designing DVD menus is not about eliminating artifacts but learning how to minimize them.

All monitors are not created equal
When designing DVD menus, look at your graphics on a TV before you create your DVD. Preferably a production monitor, but if you can only use a standard TV that will have to do. Remember, your graphics might look great on your computer monitor, but until you see them on a TV, you won’t know the final DVD will look like. In addition to artifacts, color will differ from a computer to a TV, so you will not know how it really looks until you see it on a monitor.

So how can I look at my menus on a TV without making a DVD? There are applications designed to display graphics on a TV out of Photoshop. You may need to purchase a converter that accepts firewire or USB cables from the computer and converts it to composite (RCA connector) or S-Video, unless you already have a video card with those outputs. Once converted, you can hook up your monitor as you would a VCR or DVD player. 

When testing your menu, there are several factors that will effect how your menu will appear. The type of cable used to connect to the monitor or TV can effect how well it displays. Your options (from worst to best) are:
1. Composite (RCA connector)
2. S-video
3. Component (professional analog)
4. SDI (Serial Digital Interface)

The lowest quality image will be created using a composite cable. This is the same type used in the majority of home viewing situations. If you want to see what your menu will look like in the worst case scenario, use this type. Another factor to keep in mind is all TVs are different. If possible, use a production monitor to review your menus.

Newer TVs have comb filters and line doublers. These filters help improve the TV so you won’t be seeing the raw video signal as you would with a production monitor. If you only have a consumer TV, it’s best to test your menu on several different TVs to get a good understanding of how it will display. If you are using a production monitor, make sure to turn off the comb filter to see the graphics in a raw (worst) state. After a little practice, you may be able to judge what fonts, colors, and designs will work and what won’t.

Important tools of the trade
In addition to a production monitor, it’s important to have the proper tools to create professional looking DVD menus. Two important tools are the waveform and vector scope. Explaining how to use these is beyond the scope of this article, but in short, these are engineering tools used in professional video production that measure luminance (light and dark) and Chrominance (color) levels and phase. These tools will allow you to measure video levels in graphics to determine if they are within NTSC guidelines (see Part I) and are available in hardware and software forms.

When buying software-based Waveforms/Vector scopes, some only display one line of video per field instead of the full field or frame. This does not give an accurate representation of your graphics. Professional video editing applications such as Final Cut Pro come with their own versions of Waveforms and Vector scopes, and FCP shows a full frame of video. Check your software as you may already have these tools. If you don’t know how to use them, consult your user manual, or search the web (there are many good resources out there).

Mechanics of a monitor
Now that you have all the right equipment, let’s discuss why TVs and computer monitors display images differently. A computer screen is made up of individual pixels each assigned it’s own discrete luminance (light and dark) and chrominance (color) scanned progressively. That means each line is scanned, one after another, in order from top to bottom.

A TV screen is made up fields. These fields are created by a single electron beam scanning across the phosphorus coating on the back of a picture tube. The point of this beam changes chrominance and luminance values as it scans comprising the TV picture. In a video image, each second contains 30 frames and each frame consists of 2 fields (odd/even – 60 fields a second).

These fields are not drawn progressively as with a computer monitor or on some high definition TV sets. The beam traces across the picture tube creating field one first (figure 1a) then retraces to the top of the screen and creates field 2 (figure 1b). This process is known as interlacing. The end result, the two fields appear to be seamlessly integrated into one solid picture (figure 1c). 

Figure1ABCThis happens so quickly (approx 1/60th of a second) that the human eye cannot detect it is occurring because of a phenomenon called persistence of vision. However, it is this process of interlacing that causes problems with computer generated graphics on a TV. 

Designing a menu
Now that you better understand how images display on a TV, let’s present some guidelines for designing DVD menus.

Horizontal Lines
Horizontal lines present one of the most common issues with DVD menus. During scanning, if a horizontal line is too thin it can be visible in only 1 field of video. Since the cathode ray alternates scanning between odd and even fields, the line will seem to appear and disappear causing it to twitter or flicker. By keeping horizontal lines no thinner than 3 to 4 pixels thick you can help avoid this issue. You can also try shifting the line a pixel or two up or down. Sometimes this will alleviate the problem.

s708-fig2Fonts
Fonts can be an issue if not used carefully. It’s recommended that Serif fonts be avoided. Serif fonts have small design details that often consist of horizontal lines. These elements can cause twitter. It’s best to stick with Sans Serif fonts, but there are no hard and fast rules when it comes to designing graphics for display on a TV. Just because a font is Sans Serif, it doesn’t mean it will work as different fonts have different styles.

Font size can also be an issue. A font that’s too small can buzz, crawl, or mosquito. It’s generally accepted that font sizes smaller than 18-20 points should be avoided. Although this is a good starting point, it’s not a rule. Different fonts can be larger or smaller than one another even though they may be the same point size. This is a good time to check things on your monitor. No matter what the point size, if it doesn’t look right, don’t use it. 

Some experts recommend adding a very slight blur to text that doesn’t display well. Sometimes that effects the readability of the menu. Another approach is putting a drop shadow or a glow on the fonts. This not only can help reduce artifacts, but it can add to the readability of your menu. If you’re careful when choosing fonts and test your menus on a monitor, you shouldn’t have any need to add a blur.

Chrominance (color)
As covered in Part I, staying within the NTSC color safe limits is important – but it is no guarantee. Colors, especially red and yellow, if too hot (bright), can mosquito or crawl. A good place to start is adjust them to within the NTSC limits. Review your menu on a TV and if those colors look bad, you will need to go back and drop the saturation until it looks OK. Working within a single color palette is a great way to reduce artifacting. Use a light blue font on top of a darker blue background. This makes it easier for the cathode ray to adjust between the two areas of the image.

Luminance (brightness)
As with color, white levels that are too bright can cause issues. Again, adjusting to NTSC safe levels is a good start, but you may need to do more. White on “TV White” is actually gray. If your white levels in your fonts or images don’t look adequate, drop the brightness down until it’s slightly gray. When you view this on a TV, it will look white.

Sharp Edges
As with horizontal lines, sharp edges, either in a font or in the design, can twitter or buzz. This can happen for two reasons: the edge can fall within just one field of video or there can be too great a contrast between the edge and the color next to it. When the contrast is too great, the cathode ray can’t change luminance and chrominance values quickly enough to compensate for the difference. For this reason, we get artifacting.

You can handle this one of two ways. First, although I didn’t recommend it for fonts, you can blur the edge so it creates a slight gradient between the two values. This gives the ray a series of steps to change values. The same can be accomplished using a semi-transparent drop shadow or glow. Blurring the image will also work on areas of your menu that may have a busy pattern like crosshatching or a herringbone.

Second, you can adjust the colors so the contrast isn’t as great. If you have a black element next to a white element, try changing the white to gray or some other color. Sometimes even rotating the element slightly can alleviate the artifacting.

Designing a DVD menu is a trial and error process. What may work in one instance, won’t in another. You may need to experiment with fonts, colors, and designs before you get an acceptable combination. The important thing is to recognize what works and doesn’t work and above all, test your menus on a TV.

Read Part I of this series »

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