How to Adjust Image Size?

on Monday, August 31, 2009

Again, you only need to convert the still image sizes if you plan to export the movie back to tape or DVD. If your movie will only be watched over the Web, you don’t need to convert the image. The exact steps you should use to adjust the image size vary depending on the image-editing program you are using, but in most programs, they work something like this:
  1. Open the picture in your picture-editing program.
  2. Open the dialog box that controls the image size in your software. In Adobe Photoshop, choose Image➪Image Size.
  3. Remove the check mark next to the Constrain Proportions option. Most editing programs have a similar constraining option (such as Constrain Size). Make sure it’s disabled.
  4. Change the image size to 720x534 if you’re working with NTSC video, or 768x576 if you’re working with PAL video.
  5. Click OK and save the image as a JPEG image file.
Save the image using the JPEG format because it can then be used in just about any video-editing program. If your picture-editing software gives you a quality option when you save an image as a JPEG, choose the highest quality possible if the image will be used in a movie program. Other versatile formats include BMP, PICT, and TIFF, but you should check the help system for your video-editing program to see which formats are supported.
Although the image may look slightly distorted after you change the size, don’t worry: It will look right when viewed with the rest of your video. Just remember that you only have to perform this modification if you plan to export the movie back to tape. If you plan to use your movie only on computer screens (or share it over the Internet), you don’t need to change the aspect ratio of the image.

Adjusting the image size


Most video images have an aspect ratio of 4:3, which means the width and height of the image can be divided into a 4:3 ratio. Most of the sample clips on the CD-ROM that accompanies this book have an image size of 320 pixels wide by 240 pixels high. If you do the math, you’ll see that 320x240 works out to a ratio of 4:3.
When you take a picture using a digital still camera, that picture usually has an aspect ratio of 4:3 as well. Image sizes that have a 4:3 aspect ratio include 640x480, 800x600, and 1024x768. Your computer’s monitor also probably has a 4:3 aspect ratio unless you have a newer widescreen monitor. Most TVs still have a 4:3 aspect ratio as well. Because the 4:3 aspect ratio is so common, dropping an 800x600 digital photo into a DV-based video project should be easy, right?
Unfortunately, it’s not always that easy.
Digital images are made up of pixels, which are tiny little blocks of color that, when arranged in a grid, make up a picture. Pixels can have different aspect ratios too. Digital graphics usually have square pixels, while video usually has rectangular pixels. The frame size of NTSC video is usually listed as 720x480 pixels. This does not work out to 4:3; it’s actually 3:2. However, it still appears to have a 4:3 aspect ratio because NTSC video pixels are slightly taller than they are wide.
What does all this mean? Suppose you place an uncorrected digital picture into a video program, and then you export that program back to tape. When you view the movie on a TV, the still image will appear distorted. To correct this, you need to start with a digital photo that has an aspect ratio of 4:3, and then (depending on your local broadcast video standard) change the image size to
  • 720x534 pixels (NTSC)
  • 768x576 pixels (PAL)
Use the size that matches your local broadcast video standard (see Chapter 3 for more on video standards). Before you convert an image to one of these sizes, it should have an aspect ratio of 4:3. Common 4:3 image sizes include 800x600, 1024x768, and 1600x1200.

Using Still Graphics in Movies


Although movies are all about motion, there are plenty of times you’ll want to include still graphics in your video projects. The process of importing stills into your video-editing program is usually pretty simple, but before you start plopping stills into your timeline, you should take some important steps to make sure that your images will look right. If you don’t take the time to prepare your stills, two main problems can result:
  • Images may become distorted and look unnaturally stretched or squeezed.
  • Colors might not display properly