Digital Video Concepts

iMovie makes it so easy to work with digital video that you don't really have to understand all the nuts and bolts. But getting a better sense of how things work will help you to have more confidence, and will most likely result in better-looking productions . Let's take a look as some of the basic terms and concepts related to digital images and digital video.


One of the fundamental concepts in working with digital video is the system that a computer uses to draw images on the screen. Your Mac divides the screen up into a grid of individual pieces called pixels , which are essentially individual dots that make up a picture.

It's possible for a computer to talk to a camcorder in such a way that you never have to deal with the measurement of pixels. When you capture video, iMovie automatically chooses the right settings, and you end up exporting to your camera again. When you're working with iMovie, you might never need to consider pixels, but it can be helpful to understand them, especially if you ever need to export an iMovie at a different size than the original. For example, you might want to save a special version of your iMovie to burn on a CD or put on a Web site, and when you do so, you end up saving it at a smaller size, which involves fewer pixels. Later in the lesson, we take a look at how this is done.

One typical way that you might need to work with pixels on your computer is when you adjust the resolution of your screen.


Resolution is a term that describes how much detail there is in a computer-generated image. A high-resolution image has more detail, and is considered to be a higher-quality image. Conversely, a low-resolution has less detail, and thus is of lower quality. For example, when you choose a different screen size on your Mac, such as 800x600 pixels, or 1024x768, you're changing the resolution of the screen ”and you can see that with higher resolution, more can fit on the screen.

On a Mac, you can adjust the resolution setting in the System Preferences area of your computer. If you aren't familiar with pixels already, you might want to try this to get better acquainted.

Another way to think of pixels is in terms of individual graphics that you see on the screen, such as when you are looking at a Web page. People who work with digital images make adjustments to pixel sizes all the time, such as when they take a large digital picture and make it smaller so that they can put it on a Web page. (You'll learn about this very thing when we talk about saving images files in Photoshop Elements in Chapter 21, "Introducing Photoshop Elements.")

Your Mac draws images in such a way that you don't normally notice that an image is comprised of individual dots, but to get a clearer sense of what pixels actually are, let's take a closer look. In Figure 13.14, you see an image enlarged to 1200% so you can clearly see how the computer is using individual square-shaped blocks to draw the image.

Figure 13.14. A close-up view of an image, showing the individual pixels.


Screen Size

The concept of screen size is related to pixels, because a computer screen or video image is made up of rows of pixels. There are differences between the ways that a computer and a television draws images, but to keep things fairly simple, it's generally okay to think of working with video in terms of pixels.

In the United States, televisions use a system called NTSC (National Television Standards Committee). When you design video on your computer for NTSC televisions , it is 720 pixels wide by 480 pixels high when it's displayed at full size.


When you work with video in iMovie, you can see a reduced-size version of the iMovie in the Monitor window.

If you live in Europe, you probably use the PAL system for working with video, which has a screen size of 768x576. The PAL system also uses a different frame rate, a concept that we talk about later in the hour .

As with pixels, the screen size isn't necessarily something that you need to be concerned about. In fact, you could make hundreds of iMovies and deliver them on VHS tape or through iDVD and never even consider the screen size.

One of the great things about iMovie is that it gives you the flexibility of working with video how you want. You can either let your Mac make educated guesses about how to adjust the settings, or you can go in (if you learn a bit about the kind of concepts that we talk about in this hour) and adjust things yourself. iMovie does have its limits, but as you'll see, it has a lot of flexibility as well.

Frame Rate

The frame rate of digital video is the number of images that are displayed in a second as they flash by, like frames in a traditional movie. Before television or video existed, moving pictures achieved the simulation of motion by projecting images on movie screens. This effect was achieved by rapidly projecting a succession of images on a screen, and the rate that the images are displayed was called the frame rate .

In traditional movies, the individual images and frames are contained in large reels, and they go by at a rate of 24 frames per second. The frames per second measurement has been adopted by digital video, but the measurement depends on a variety of factors, including the country you live in and the way you want to deliver your digital video. For example, if you use the NTSC digital video system, the measurement is most often 29.97 frames per second (fps).

So, as with other settings, you can let iMovie decide what frame rate setting to use. But if you want to, you can tweak your iMovie and change the frames per second manually.


Compression is another aspect of video that affects the quality of the image and the amount of space that digital video takes up on a hard drive or a disc such as a CD or DVD. Most digital video has some kind of compression already applied. For example, when you simply capture video from your camcorder into iMovie, iMovie compresses the video slightly so that it can display your video on the screen and store it on your hard drive without taking up too much space.


Compression is similar to what people do when they stuff or zip a file to make it smaller so that they can email it. Compression is a kind of digital squeezing.

As with some of the other concepts in digital video, you might not need to think much about compression unless you want to start experimenting with sharing your iMovies in different formats such as email, CD-ROM (if you have a CD burner), and DVD (if you have a DVD burner ).


Timecode is simply a fancy term for keeping track of where you are in your iMovie. At first glance it doesn't seem like a big deal, but it can come in very handy if you watch your video ahead of time and mark points where you want to edit it.

In iMovie, the timecode is displayed directly to the right of the playhead, and reflects the number of minutes and seconds of video. (A digital video timecode is often displayed with seconds and frames, rather than minutes and seconds, but iMovie makes it easier by displaying minutes and seconds.)

Sams Teach Yourself Mac OS X Digital Media. All In One
Sams Teach Yourself Mac OS X Digital Media All In One
ISBN: 0672325322
EAN: 2147483647
Year: 2003
Pages: 349 © 2008-2017.
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