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The biggest difference between types of bitmaps is that they can be of different bit depths. There are five different bit depth settings. Bits refer to the amount of information stored for each pixel of a graphic. A 1-bit image has only one piece of information: on or off. An 8-bit image has eight pieces of information, which corresponds to 256 possible combinations. This means that every pixel can have 256 possible colors. Here is a rundown of some of the possible bit depths:

  • A 1-bit bitmap contains only black-and-white pixels. It's small, because only “on” or “off” data has to be stored for each pixel, not a color value. 1-bit bitmaps can be useful because you can define the colors of the two types of pixels in them to different colors depending on the sprite. So, a single 1-bit member can be used multiple times to display graphics with different colors.

  • A 4-bit bitmap contains 16 colors. On the Macintosh, you can customize these 16 colors. In Windows, you can use only one 16-color palette: the Microsoft VGA palette. If you are making your Director movie for a 4-bit machine and intend to distribute it cross-platform, use the Windows VGA palette.

  • An 8-bit bitmap contains 256 colors. These 256 colors correspond to a color palette. This palette contains black, white, a small range of grays, and a general selection of basic colors. You can customize an 8-bit palette both on the Macintosh and in Windows. Director ships with a number of built-in 8-bit palettes. You also can import custom 8-bit palettes into your Director movie either with images that use them, or on their own in the standard palette format (PAL). They are then stored as cast members.

  • The 16-bit, or thousands of colors, color depth contains 65,536 colors. This color depth was created to closely match the color values of a normal television set. This color depth does not have a palette associated with it.

  • The 24/32-bit, or millions of colors, color depth contains 16,777,216 colors. This is the maximum numbers of colors that can be viewed on a computer monitor. This number is actually overkill because a person with normal vision can perceive only about nine million colors. This color depth does not have a palette associated with it.

    The notation 24/32 might seem a bit odd. The 32 refers to total bits of information: 24 bits for everyday colors and 8 bits that deal with Alpha channel information or other special effects. You can't, however, work in 24 bits; when 24-bit terminology is used, it actually means a 32-bit resolution.

Using 8-bit images wherever possible is a good idea. An 8-bit image draws faster than a 16- or 32-bit image because the computer can process the smaller 8-bit image faster than a larger one. However, if your movie requires better color, use a higher setting.

Two things are conspiring to make 8-bit images obsolete. First, just about every consumer-level computer sold in the last three years is capable of displaying 32-bit color. Second, Director's bitmap compression and JPEG compression for Shockwave movies can often make 32-bit images almost as small as their 8-bit counterparts, and these 32-bit images look much better.

An 8-bit bitmap can use only 256 colors at one time. However, a technique known as dithering can make the color range look wider. Dithering is the process of approximating a color by placing pixels of different, but similar, colors next to one another.

Using Palettes

You can use Director and bitmaps without knowing much at all about palettes, but it helps to understand them. Several palettes are built in to Director. These include the Mac system palette and the Windows system palette. Each acts as a default palette for Director running on the system.

Strangely enough, these palettes are not the same. This is where a lot of trouble begins. If you decide to make your movie work with 8-bit graphics, you must choose a palette in the Movie Properties dialog box. But which standard palette do you use? The Mac palette displays fine on Macintosh computers, but not on some Windows machines, and vice versa.

In fact, if the user's monitor is set to use 16- or 32-bit color, the palette issue will never arise. This monitor has enough colors available to display any palette. However, if a computer is set to use an 8-bit monitor setting, it means that it can display only 256 colors at one time.

If you want to use 8-bit images and you don't need to stick to a standard palette, it might be a good idea to create a new palette that is optimized to display your collection of graphics as best as possible. This palette can be imported as a cast member and referred to just like the built-in palettes. Programs like DeBabelizer on the Mac and Brenda in Windows can create custom palettes for you. Also, the PhotoCaster Xtra can import a series of PhotoShop images and create a new palette at the same time.

Showing a movie that uses a palette that differs from the one the system uses causes the computer to adjust and shift to your movie's palette. This is fine as long as the movie takes over the entire computer screen. However, if a window of another application or the desktop shows through, it will display in the wrong colors.

In addition, showing two 8-bit images that use different palettes also causes problems. Two totally different palettes would mean that you are asking the computer to display 512 colors at one time. Because it can't do this, some of the colors shift.

Using graphics that are 16- or 32-bit also causes problems for users with 8-bit displays. The graphics probably use far more than 256 colors, so Director attempts to compromise when displaying them. The result might be that your graphics do not look very good.

Choosing the Bit Depth

You should think about palettes and bit depth before starting your project. What will your users be using? If they have 32-bit monitors, you know that you have the option to use 32-bit graphics. If many have only 8-bit capability, 8-bit might be your only option.

The Web palette uses only 216 colors that are shared by both palettes. The rest of the colors are not used, but are reserved to enable the system to display the desktop and other elements.

If your project is focused on deep, complex images, such as photographs, you might want to consider 16- or 32-bit graphics if possible. However, remember that they are two or four times larger than 8-bit bitmaps. Your Director movies will be much larger as a result. However, much of this excess file size disappears when you make Shockwave movies for either the Web or a projector.

If you know that most of your users have either Macintosh computers or Windows, the choice of a palette is obvious. Otherwise, consider which one is appropriate for both platforms or perhaps construct a new one. If your movie will end up as a Shockwave movie on a Web site, using Director's built-in Web palette might be the answer. It displays well on both Mac and Windows.

The options can be confusing. If you are just learning Director, stick to using the default palette of your system for now.

For more information on cross-platform development, see Developing for Both Mac and Windows p. 700 (Chapter 35, “Cross-Platform Development”)

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