Dr. Website
Reducing Animated GIFs Means Cutting Frames Down to Size
Dear Dr. Website®: I am designing an animated GIF for my site. Each frame measures 468 by 60 pixels, and there are 10 in all. The problem is that I want the file to be no larger than 10 Kbytes. I reduced the colors down from 8-bit to 4-bit, but it is still too large at 28 Kbytes. Can you suggest anything I should do?Animated GIFs have become a wildly popular addition to many Web sites over the past year, but many designers are now looking past the novelty of the technology and are holding these snazzy images to the same standards they apply for ordinary GIFs. In other words, animated GIFs should serve a useful function, have colors optimized across platforms, and take up no more space than necessary.
Some graphics utilities for creating animated GIFs, including GIFBuilder, have responded to these needs by making use of a well-known video compression technique called frame differencing. Frame differencing builds on unique features of the information that makes up the moving image. This technique lets you cut the file size of your animated GIFs by replacing the parts of the image that change, instead of pasting in entire new frames each time. Advanced users can even automate GIFBuilder's operation with AppleScript.
Ulead's PhotoImpact GIF Animator is a Windows utility that uses a smart frame-comparison technique that stores only the pixels that change from frame to frame. GIFBuilder, by Yves Piguet, is a Macintosh program for creating animated GIFs that lets you take advantage of a frame optimization feature; it tracks a bounding rectangle around the pixels that change from one frame to the next and updates the image accordingly.
As you've discovered, optimizing the color palette used throughout all the frames in an animated GIF is important for trimming its file size. When you create an animated GIF, you can choose whether to use a global palette or let each frame use its own local palette. Using a global palette cuts down on the number of colors used, and thus reduces your file size.
You might also want to read Optimizing Animated GIFs, an article by Andrew King at the webreference.com site that includes some innovative, step-by-step details for reducing animated GIFs to the smallest possible file size.
Batching Image Conversions
Dear Dr. Website®: I have a whole bunch of images saved as TIFFs that were used in my company's print ads. Now, I need to convert them to GIFs for our Web site. Is there an easy way to save them in a different file format all at once?There are a number of batch conversion utilities for graphics designed to suit the need you just described. Without such a program, it could take you hours to open all your individual graphic files and save as another format. The situation becomes more critical, however, if your graphics' native application does not support any Web graphic formats.
Quarterdeck's HiJaak 95 for Windows and Equilibrium's DeBabelizer for Macintosh are two commercial graphics packages that are designed to handle large batches of file conversions. Additionally, users of the cross-platform Adobe Photoshop have several third-party batch file conversion utilities at their disposal for speeding up this kind of routine task. These utilities include DayStar Digital's Photomatic and Gryphon Software Corp.'s Batch-It, two commercial Photoshop-specific programs for automating certain graphics processes. Users of the new Photoshop 4.0 can now enjoy batch processing capabilities that are built right into the application.
On the shareware side, Paint Shop Pro is a good Windows-only program that lets you convert many different file formats to JPEG or GIF; you can choose a Batch Conversion menu item right from the File menu. For Macintosh users, Imagery is a good tool for performing batch file conversions; you can download it from many Macintosh shareware archives.
Reprinted from Web Week, Volume 2, Issue 20, December 16, 1996 © internet.com Corporation All rights reserved. Keywords: Date: 19961216
