Dissolving with palette crossfades

Dalai Lama Both Pope

One bitmap, two images: smooth on any machine!

The Director demo movie below demonstrates a little-known technique for smoothly dissolving between two images using nothing but a palette transition. The cast of this movie uses only a single bitmap which contains two different images: the 14th Dalai Lama and Pope John Paul II. Selecting a different palette for the bitmap displays an entirely different image. A smooth palette transition between two palettes, therefore, accomplishes a smooth dissolve between one image and the other.

Since not a single pixel of bitmap information needs to be changed as the images crossfade-- only the palette slot values are changed-- this effect looks just as good on a low-horsepower machine as it does on a high-horsepower machine. It also looks just as good on Windows as it does on the Macintosh-- which isn't the case at all for Director's own built-in 'dissolve' transition (which is painfully slow on Windows compared to the Mac, and which is slower on larger images).

There are limitations to this technique. The effect requires a 256-color video mode, and the two images must each be limited to a range of 16 colors (though dithering is possible). This usually means that greyscale or tint ramp images work best with the technique. Transitions like these are great for splash screen movies, or sections of a multimedia project that are more for presentation or visual effect than interactivity.

Currently, it's rather difficult to build images like this. I have used a combination of techniques including Equilibrium Systems' Debabelizer graphics processing software and a custom Director 5 movie I wrote that composites the two 16-color images and palettes, using the FileIO XObject to read and write .BMP files on disk. This movie is available for download below if you're interested in building images like these yourself. Because of a 64K limitation in the Windows version of the FileIO XObject, and the requirement for Debabelizer in some of the steps of the production process, the image creation movie is designed for use on the Macintosh only. Unfortunately, I can not support this as a product at this time, so you're more or less on your own with the provided handlers and minimal documentation. Enjoy, and please email me any interesting crossfade images you create!

If you like this technique and would like to see me develop and release more polished tools for generating image transitions like this as a commercially supported product, please email me at gpicher@maine.com. If the feedback warrants it, I will develop a crossfade toolkit that makes the process fast and simple. Regardless, I'd appreciate it if you email me when you pick up a copy of this demo movie or the image creation movie; I'll keep you informed about any future tools I may release using this technique.



The demo packages contain a Director 4 demo movie (openable and usable without modification in Director 5) and a Read Me document. This demo movie works the same on Mac and Windows. Different palettes are used to display the image on the two platforms, to correct for the differences in gamma (brightness curves) between the two platforms. This technique is useful when Mac-authored Director movies appear dim and desaturated on Windows, or when Windows-authored Director movies appear bright and washed-out on the Mac.

The image creation package contains a Director 5 movie, with some sketchy documentation contained within the movie itself.

Choose the most convenient format for downloading. Hopefully, storing these movies in these two formats will make them accessible to most anyone anywhere, no matter how you connect to the Internet.

Small Dirigo logo

Glenn M. Picher: Dirigo Multimedia
Back to Glenn's home page