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FastGIF Version 2.0 Users' Manual GIF and `Graphics Interchange Format' are trademarks (tm) of CompuServe Incorporated, an H&R Block Company. FASTGIF v2.0 is Copyright (C) 1987 James C. Beebe. All Rights Reserved. TABLE OF CONTENTS 1. FEATURES 1 2. USER SUPPORTED SOFTWARE 3 3. ABOUT GIF 4 4. FASTGIF HARDWARE SUPPORT 4 5. DISPLAY MODES 5 6. OPERATING MODES 6 7. MENU MODE 6 8. SLIDE SHOWS 8 9. FILE ORGANIZATION 8 10. PROGRAM DESCRIPTION 10 11. FUTURE 12 12. ERROR MESSAGES 12 1. FEATURES FastGIF is an off-line decoder for the display of Graphics Interchange Format (GIF) images on IBM personal computers or compatibles, equipped with EGA or VGA display systems. GIF was developed by CompuServe and features: Machine Independence GIF files may be exchanged between different computers and graphics systems. With the proper decoder, each system will display all GIF files to the best of the machine's capabilities. This allows the widest possible audience for artists distributing their images in the GIF format, and an immense selection of images for those who enjoy viewing computer images. Compression GIF files are compressed using a highly effective adaptation of the LZW algorithm. Communication and storage costs are held to a minimum with the compression scheme. Since all GIF decoders can uncompress GIF images, machine specific archival utilities are not required for the images. Performance The Graphics Interchange Format allows for images up to 65535 dots wide by 65535 lines high, containing up to 256 colors selected from up to 16 million different colors. While no graphics hardware has these capabilities today, the format will be able to handle the interchange of raster graphics well into the future. FastGIF was developed by James C. Beebe, and features: Speed FastGIF, as its name implies, is highly optimized for speed. On any given computer, no current decoder achieves anywhere near the display speed of FastGIF. Reportedly, fast '286 and '386 computers using FastGIF display images much faster than other computers utilizing specialized graphics support hardware. FastGIF is offered as evidence that the Intel family of processors and the IBM family of personal computers are as suitable for high performance graphics as any series of microprocessors in any current personal computer! FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 1 Visual Quality FastGIF does not sacrifice the visual quality of displayed images for its speed. In fact, no other current GIF decoder for the EGA achieves comparable visual quality on as wide a range of images as FastGIF. Hardware Support While FastGIF does not support systems less capable than the 256k EGA, its support of these systems is extremely complete, including the ability to vertically scroll images which cannot be completely displayed on an EGA without multiple sync rate monitors. User Interface FastGIF provides a friendly user interface, including selection of images from an onscreen menu, without requiring a slow or complicated process to select and display images. Slide Shows FastGIF will display a series of images automatically by following a user-generated command file. User Supported FastGIF is distributed for free trial, with no license fee required until after the free trial period. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 2 2. USER SUPPORTED SOFTWARE FastGIF is user supported software. FastGIF represents as large a creative and programming effort as many commercial software packages costing hundreds of dollars. In the spirit of user supported software, FastGIF is made available for a free ten day trial period. If you find FastGIF to be useful, you are obligated to pay for continued usage. Because of the low distribution costs of user supported software, FastGIF may be licensed for non-commercial use on one machine at a time (like a book) for the cost of $19.95. For commercial use, defined as a use of FastGIF where an individual or commercial enterprise reasonably expects to use of FastGIF to result in a profit, FastGIF may be licensed for $100.00 for up to ten computers at a single site or set of contiguous sites. FastGIF is the copyrighted property of James C. Beebe. All rights are reserved other than those rights specified above. If you do not pay for a license for the continued use of FastGIF, you are obligated to discontinue its use after the ten day trial period. FastGIF may not be modified by anyone other than the author. FastGIF may be distributed to others only in its complete, unmodified form, with no fee charged other than a fee for media and duplication. No matter how you received your copy of FastGIF, you are obligated to pay for a license after the trial period. FastGIF is available to be included with a product, or to be incorporated into a product. Contact James C. Beebe for further information. All registrations will be promptly acknowledged. James C. Beebe 2170 Dow Drive Akron, Ohio 44313 Compuserve 74746,2444 FastGIF is made available for your enjoyment in the viewing of GIF images. All warranties are disclaimed, including consequential warranties. It is your responsibility to determine whether FastGIF is suitable for your purposes. The high- performance display of graphics images may not be compatible with all combinations of graphics hardware. Make certain that your hardware is suitable for use with FastGIF before risking machine damage. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 3 3. ABOUT GIF GIF files are a highly compressed, machine independent format for the distribution of raster-based color graphics information. The GIF file format was defined by CompuServe, who has made it available for public usage. Over 1000 GIF files suitable for viewing with FastGIF are available on the PICS forum of CompuServe. There are also encoders and decoders for a variety of different computers and graphics adapters available in the Data Libraries of the PICS forum. Because the GIF format is machine independent, the visual quality of files may vary widely. A computer equipped with an EGA card, especially with one of the extended EGA cards and a monitor with multiple scan rates, and running FastGIF software, is among the best at displaying GIF images. However, certain files may not display well with any combination of hardware and software. The developers of GIF decoders continue to search for ways to improve the visual quality of images displayed using the GIF system. 4. FASTGIF HARDWARE SUPPORT FastGIF requires an EGA card with 256k of memory and an EGA monitor or a VGA system as furnished on the higher models of the IBM Personal System II. Certain non-IBM EGA systems can be equipped with monitors capable of switching to multiple scan rates to provide higher resolution. FastGIF supports many of these systems with "command line switches." Note that if you have a standard EGA monitor, you should NOT use these command line switches! The switches are preceded by a hyphen (-) or a slash (/). The switches in FastGIF are: a Ahead Systems 640 x 480 (mode 38 decimal) g Genoa 640 x 480 (mode 115 decimal) t Tseng 640 x 480 (mode 37 decimal) v VGA 640 x 480 (mode 18 decimal) m### Use DECIMAL value ### to select 640 x 480 f Do not expand pictures; use only 640 x 350 modes. Vega 480 line mode is automatically recognized. If none of the switches are given, the default video mode will be EGA mode 16, but pictures will be decoded as though a 640 x 480 mode was available. If the entire image does not fit on the screen, the SHIFT keys may be used to scroll the image vertically to view the entire picture. The left SHIFT key scrolls the picture up, allowing more of the bottom of the image to be seen. The right SHIFT key scrolls the image back down, allowing more of the top of the image to be seen. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 4 These command line switches may be given any time FastGIF is started. If your video hardware can benefit from one of these switches, you may want to create a batch file to automatically issue the switch. For instance, if you have a Tseng card with a multiple scan rate monitor, you might create a batch file as follows: C>copy con fg.bat FastGIF -t %1 ^Z <-- this is generated by pressing F6 or control Z. You could then start FastGIF by typing: FG image.gif 5. DISPLAY MODES FastGIF has two different ways to display graphic images to the screen. The first way is to decode the file directly to the screen. When this is being done, you will see the image "painted" on the screen as you watch. This method is used: -- if you give a single filename on the command line. -- if you press Return or F10 in menu selection mode with no files currently selected. -- for the first file displayed in a slide show. The other method of displaying an image is to first decode it in the background, and then to quickly copy the image to the screen. When this is done, the picture will "pop up" from a momentarily blank display screen. This method is used: -- for images selected with the space bar from the menu. -- for files after the first file in a slide show. One of the most popular image sizes is 320 x 200. Unless the -f option is given, FastGIF will display these images as 640 x 400 images. Since there are four pixels used on the display for each pixel in the original image, extended color resolution can be provided on these images, by carefully selecting the colors of the four dots used to display each image pixel. This process is called "dithering", and is an important part of FastGIF's ability to provide high visual quality on these images. Dithering is ONLY used on images decoded in the background; images decoded directly to the screen are NOT dithered. If you wish to compare a 320 x 200 image with and without dithering, view it by decoding directly to the screen and by decoding in the background. The difference can be amazing! FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 5 6. OPERATING MODES FastGIF can be operated in several different modes. The simplest mode is invoked by giving a single filename (without wildcards) on the command line of FastGIF. The image will be decoded directly to the screen, and if it is too large to fit on a single screen, it may be scrolled using the SHIFT keys. Press the return key to return to DOS. An example would be: C>FastGIF trees The second mode is menu mode. This is invoked by giving no file argument on the FastGIF command line, by giving a file argument containing wildcards, by giving a directory name as the file argument, or by giving a drive name as the file argument. Further details on menu mode are given in the menu section below. Examples: C>FastGIF C>FastGIF t*.gif C>FastGIF \pictures C>FastGIF a: The third mode is slide show mode. This is invoked by giving the name of the slide command file, preceded by the "@" character, on the command line. Further information is provided below. An example: C>FastGIF @myslide 7. MENU MODE FastGIF's menu mode provides a "user-friendly," intuitive method to select files from a menu displayed on the screen. Special care has been taken to make menu mode easy for advanced users, as well, by minimizing the number of keystrokes required to select and display files. Help screens are available by pressing F1. The help screens give a condensed version of the information in this manual, and should be sufficient to allow operation of FastGIF without referring to the manual. Menu mode allows the selection of a series of images for display, as described below. The time delay between these images is selected by pressing F2, then entering a delay time (in seconds) at the prompt. A negative entry will cause FastGIF to wait for a key to be pressed between images. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 6 When FastGIF is invoked in menu mode, a list of files will appear on the screen. The exact presentation of the filenames will vary with the number of files; FastGIF displays as many files on screen as possible, and reduces the level of detail about the files as the number of files increases. (This strategy allows full information on up to 46 files, and allows filenames only for up to 184 files on a single screen.) If more than 46 files are on a screen, the detailed display may be selected with F4, and the compressed display selected with F3. Four function keys change the order of the files displayed. These keys are: F5 -- Sort by file size F6 -- Sort by file date/time F7 -- Sort by filename (default) F8 -- Sort by file extension, then filename. The F9 function key displays additional information about the file, including the GIF version number, the image size of the file, and the color resolution. This information is taken from a header included in all GIF files, and its accuracy depends on the accuracy of the header information. Files are selected for display by moving through the file list with the cursor keys. If more than one screen of files is available, the Home, End, PgUp, and PgDn keys move through the screens. To select a file for display, press the space bar. The first file selected is decoded in the background, and appears in red while it is being decoded, then in green when it is ready for display. Later files appear in yellow if selected. The first file decoded cannot be unselected; later files can be unselected by pressing the space bar. Files are displayed in the order they are selected. While the first file is being decoded, the keyboard may feel a little sluggish. This is due to the computer being shared between decoding and the onscreen presentation. To display the selected files, press return or F10. The selected files will then be displayed on screen, with the appropriate delay time. Press return after all files have been displayed to return to the menu. If the return key is pressed when no files have been selected for display, the file under the cursor will be decoded to the screen. Refer to the discussion of image display modes above for the differences between decoding to the screen and background decoding. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 7 The ESC key will abort a series of images being displayed, or will return to DOS from the main menu. 8. SLIDE SHOWS FastGIF allows the presentation of user scripted slide shows. A slide show script is an ASCII file, created with a text editor, such as WordStar in non-document mode, which contains a series of command lines. There are three types of command lines: image filenames, delay settings, and the quit command. A slide show is presented when FastGIF is started with the name of a slide show script, preceded by the '@' sign, on the command lines, as: FastGIF @my.sld Images for the slide show are specified by entering their filenames into the slide show script. Wild cards may be used. Each file specification must be on a separate line. The time each image is presented on screen is controlled by the delay specification. This is a line in the command file containing a hyphen, the character 'd', and the time delay to be used. If a negative delay value is given, the slide show display waits for the return key to be pressed before displaying the next slide. Slide shows loop. When the end of file is reached, the program starts again from the beginning of the file. The -q command in the script will cause the program to exit at that point. The program will also exit if the ESC key is pressed during execution of a slide show. An example of a slide show script: -d10 ..display each slide for 10 seconds zap*.gif ..display all gif files starting with zap pirate.gif ..display pirate.gif pics.gif ..display the pics logo -d-1 ..go to manual delay -q ..quit when key is pressed 9. FILE ORGANIZATION Keeping track of all of your image files can be difficult, even with a program like FastGIF that shows you a set of image files on a menu. The file selection method in FastGIF can assist you in this task, however. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 8 One strategy is to keep all of your image files with the CompuServe extension of .gif in your current directory... perhaps the root directory of a floppy disk. If you start FastGIF from this directory, all of your image files will be shown on the screen. Hard disk users tend to move from directory to directory. To allow FastGIF to find image files from any directory, you can keep your image files in a directory named \GIF on your current drive. If the directory containing FastGIF is included in your PATH command, you can start FastGIF from any directory and select from the image files in your \GIF directory. If you want to limit FastGIF to a certain group of files, you can use one of two different methods. The most versatile is to use different extensions for the different groups of files, keeping all image files in a single directory. As an example, if you have a large group of "comics" images, you could change the extension on these slides to .cmc, then, to start FastGIF with only the comic slides in the menu, you could use: C>FastGIF *.cmc To see all of the other images, start with C>FastGIF *.gif To see ALL of the images on the same menu, start with C>FastGIF *.* A similar strategy could be used with subdirectories. If you want to segregate your "adult" images, they could be put in a subdirectory named \PBW. You could then view the adult images either by changing the directory to \PBW before starting FastGIF, using just C>FastGIF or by starting with the command C>FastGIF \PBW The other images could be brought up by starting FastGIF from any other directory, without the \PBW argument. This strategy does not permit starting FastGIF with all images, as the extension strategy does. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 9 10. PROGRAM DESCRIPTION For those interested in the technical details of FastGIF, the program was developed over a four month period, starting with the specification and sample code provided to GIF developers by CompuServe. The program evolution followed a series of goals, with each goal being substantially reached before development started on the next goal area. All coding followed highly structured design standards, with exceptions limited strictly to cases where significant measurable performance improvements could be demonstrated. The first goal was to improve the decoding and drawing speed of the example program. To this end, the program was recoded into assembly language. A series of iterative improvements were made to the decoding and drawing modules of the program. A performance analyzer was used to determine the areas of the program where the largest portion of execution time was spent, so that effort was constantly focused on the "hot spots" of the program. Accurate measurements of time to display an image multiple times were used to measure the effects of potential improvements. The second goal, which was largely unsuccessful, was to improve the color selection strategy for images displayed on the EGA. Strategies attempted included IQY and Hue/Saturation/Luminance strategies, with gamma correction and several weighting techniques, including non-linear weighting. Many of these techniques provided improvement on some images, but resulted in significant degradation of other images. The current version of FastGIF has reverted to a rather simple RGB selection for non-dithered pictures, which, while it may not provide an optimum color selection on any one image, does not cause degradation of images, either. At the same time, the technique used for minimizing the limitation of the 16-color EGA palette was developed, and this technique has been quite successful. The algorithm used consists of avoiding duplications in the palette until all entries have been used, then selecting the closest match from colors already in the palette for colors once the EGA palette has been filled. This technique is quite successful on most images with up to 32 colors. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 10 The next goal was the user interface and path strategy. Because quite satisfactory performance can be achieved in a high level language in this area, the user interface is coded in Borland's Turbo C. Assembly language routines are used for screen writing. It was at this time that the improved "feel" of background decoding was realized; the implementation of background decoding was relatively straightforward due to the structured techniques used in coding the decode-to-screen subroutine. The path strategy is used to take a user-supplied filename and generate a filespec. The strategy, a small portion of the "natural" user interface, was rather difficult to develop, and the first test version released to the developers contained significant bugs. Basically, the strategy allows the entry of ambiguous filenames by the user, and using default extensions (.sld for slide command files, .gif for images) and the default directory (\gif), determines the intended user filespec. As the result of conversations with other developers on the Developer Subtopic of PICS, it was decided to investigate the potential of dithering pixels for improved color performance. One of the most difficult problems was in developing an algorithm that would permit good visual performance without an excessive speed penalty. The algorithm selected depends upon a table which is generated by an optimized Turbo Pascal program, compiled using the '87 package, and running on a fast AT clone with a '287. The table generation program requires about 15 minutes to execute! Several iterative developments have resulted in substantially better visual quality than exhibited by the first implementation of the dithering algorithm. The current dithering algorithm depends on expanding pixels from the image file into four dots onscreen. This works well with 320 x 200 files displayed on 640 x 480 extended EGA systems with multiple scan rate monitors, but leaves out the standard 256k EGA, and normal EGA monitors. To allow these users to enjoy the improved color rendition available with dithering, vertical scrolling of graphics images was implemented. In its current form, the scrolling is automatically bounded by the size of the image, allowing a natural "feel". FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 11 11. FUTURE In the future, the developer of FastGIF intends to investigate additional goals for the program. These goals include improvements to the dithering algorithm and the possibility of dithering pictures larger than 320 x 200. A new program, using the GIF decoding, dithering, and screen displaying modules from FastGIF, will be developed to allow real-time, on- line viewing of GIF images. Additional support will be developed for the VGA, using both its 320 x 200 x 256 and its 640 x 480 x 16 modes, and taking advantage of its larger selection of colors. Support is also intended for the rumored super VGA's, with 640 x 480 x 256 capability. These enhancements and additions will be announced in the PICS forum. 12. ERROR MESSAGES Bad Separator Character '*' The internal format of the GIF file is inconsistent with the definition. Report the error to the Sysop on the forum where the file was found. Cannot open slide file x:\dir\filespec.ext The indicated slide file could not be opened. Respecify with a filespec that will select an existing file. Early End of File The internal format of the GIF file is inconsistent with the definition. Report the error to the Sysop on the forum where the file was found. Error Expanding Data The internal format of the GIF file is inconsistent with the definition. Report the error to the Sysop on the forum where the file was found. Error Reading Extension Block The internal format of the GIF file is inconsistent with the definition. Report the error to the Sysop on the forum where the file was found. Error Reading Image Head The internal format of the GIF file is inconsistent with the definition. Report the error to the Sysop on the forum where the file was found. Insufficient Memory to run FastGIF FastGIF cannot allocate enough memory to operate. Free up some memory by removing TSR programs (such as Sidekick), and try again. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 12 No Matching Files FastGIF was not able to find any files matching the filespec on the command line. Not a GIF File The header on the file does not indicate a GIF file. Check that this is a GIF file you have downloaded. If it is, verify your download process (using a protocol such as XMODEM or CIS B protocol). If the file still will not decode, notify the Sysop on the forum where the file was found. Unrecognized Option * The option character given in the command line was not recognized by FastGIF. Refer to this documentation for the correct option characters. FastGIF V2.0 (c) 1987 James C. Beebe 74746,2444 Page 13