![]() If they don't use a majority of the same colors, you'll see a flicker when the image remaps. Navigator loads the local palette for the next image while the current image is still displayed. When you use local palettes, Netscape Navigator 3.0 and below has a bug that causes a "flicker" effect. Unless you have widely changing colors, it's a good idea to stick with an optimized global palette. (In such a case, the bit depth would be reduced from seven to six bits, a savings of over 14 percent.) Animated GIFs can have one global palette or multiple local palettes attached to each image. Think powers of 2-if a palette is just above a power of 2, say 66 colors, and you reduce it to 64, the file size will drop. GIF file size is directly related to bit depth, and decreases dramatically when you reduce by two bits or more. Minimizing the color palette is good way to reduce the file size of any type of GIF image. First, we'll reduce the color palette later, we'll concentrate on paring pixels. What distinguishes the different animation programs is how efficiently they handle color palettes and frame changes. Obviously, there's more to gain by optimizing the key frame, so minimizing the color palette and complexity of the initial frame is very important. In our case, the key frame of the minimum bounding rectangle is 2948 bytes, while the motion frames range from 395 to 629 bytes. The animation now consists of an initial full-sized "key" frame and several "motion" frames. (This technique is also common in game animation.) Table 2) version but are dramatically smaller. Overlaying these changes on an initial, full-sized "backdrop" frame creates animations that appear identical to the full-frame (See The secret of shrinking animated GIFs is to save only the parts of the animation that change from frame to frame. Since animated GIFs are essentially multiple GIFs with timing and transparency information, the same optimization principles apply: Minimize colors and maximize crop. With seven frames, our mascot penguin took 21K to waddle across the screen see In conventional GIF animation, each additional full-size frame adds a significant percentage to the file size (1/number of frames*100). After deducting for our 1.2K background and 4K of text, we realized each GIF could be no greater than 5K in size. Feathering the foreground graphics made the background graphic appear to be the foreground, and vice versa. The first two pages have four animations, a static logo, and a seamless background "ice" JPEG. We set a limit of 30K total per page and chose a single visual theme: an iceberg, with melted portholes showing movement outside the berg. When we designed, we wanted an eye-catching look with lots of movement that didn't take long to download. The typical maximum size for a Web page, including all its embedded objects, ranges from 20 to 30K per page, which translates into an average total download time of about 10 to 15 seconds for a 28.8 modem. Webmasters usually base a site's design constraints on its content and its visitors' available bandwidth. I'll walk you through an animation we optimized for, and discuss the specific issues, techniques, and available software. If you think you can do better, we invite you to take the penguin challenge (more on this later). ![]() This article shows how to create what we think are the smallest possible animated GIFs. Finding GIF images that are browser friendly and small in file size is another matter, however. In the sixteen months since they first appeared on a Web page, animated GIFs have spread through the Web like wildfire, and with good reason: They're easy to make, easy on servers, and ideal for smaller animations.
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