a quick and dirty utility for creating transparent GIF images
written by Aaron Giles (giles@med.cornell.edu)
version 1.0b3, 9 August 1994
This is the third beta release of Transparency, an extremely simple free utility for setting the transparency index in GIF images. Transparent GIF images are most commonly used as inline images in WWW pages, though they may have other uses as well.
Transparency is shipped, like all my software, as a fat binary, running incredibly quickly on PowerPC machines.
This is a beta release. If you find any bugs or have any comments, please email me at giles@med.cornell.edu. Thank you.
GIF, or Graphics Interchange Format, is a compressed graphics format developed by CompuServe in 1987. The original specifications allowed for only simple images, but a new revision in 1989 created a host of new options for GIF images. One of these options was the ability to choose one color in the GIF's color table which maps transparently when displayed. This feature has turned out to be quite useful when used with WWW browsers which have non-white backgrounds (which is pretty much all of them anymore!)
Just because you created a nifty new transparent GIF image doesn't mean that it will automatically get displayed properly in all WWW browsers. To date, only NCSA Mosaic for the Macintosh versions 2.0a3 and later support transparent GIFs. The MacWeb client software does not. Here is a brief summary of a number of WWW browers, listing those which do and do not support transparent GIFs.
The following browsers support transparent GIFs:
The following browsers do not support transparent GIFs:
As of Transparency 1.0b3, the limitation on how complex the transparent region can be has been removed. I have also convinced the NCSA Mosaic developers to use my new code for handling transparent images with arbitrarily complex regions; look for it to become available sometime soon.
I should also mention that there are no features allowing you to scroll around an image; Transparency is not intended as a GIF viewer. Because it is targeted as a quick solution to setting transparent colors for WWW images, it assumes that the images it is dealing with are monitor-sized or smaller.
Transparency's general operation should be pretty straightforward: you can either drag a GIF image onto the Transparency icon, or you can manually open up the Transparency application, choose "Open GIF..." from the File menu, and select which file you wish to work on. Transparency will then open up the image and display it onscreen for you in a window, against a gray background.
To change the transparent color index, click and hold anywhere inside the image window. A small palette of the GIF's color table will pop up, from which you can select a new transparent color or "NONE", to disable all transparencies. Once you release the mouse button, the image is redrawn against the gray background, to let you see what the resulting transparent image will look like.
When you click in the image, Transparency determines the color you clicked on and positions the color table palette such that the mouse pointer is automatically positioned over that color. This is a particularly useful shortcut for setting the color: simply click anywhere in the background color, release the mouse button without moving the mouse to a new color, and you have made that color the transparent one. Sometimes, however, this will cause the color palette to be drawn partially offscreen; just move the image window to a more convenient location and try again to fix this problem.
After you have finished with the image, you can save the resulting GIF by choosing "Save as GIF89..." and choosing an output filename.