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Bitmap Graphics in Flash

One of my favorite sites is Jacquie Lawson E-Cards. I have subscribed to her ecard membership for many years and I still feel that her FlashR ecards are some of the best on the web. There are several reasons for the high quality of her ecards including the professionally produced background music, animations that tell a story and the beautiful artwork.

For many years, Flash animators used only vector based images in their Flash projects. It seemed these animators felt that they needed to use only vector images to keep the file size of their project to a minimum. Jacquie Lawson was one of the forerunners to use bitmap, or raster, images in her animations. However, with better image compression and improvements to the Flash Player (now version 9), this is no longer the case. If you check most ecard websites today, you will see a change in the artwork used in their ecards. Flash animators are moving toward the use of more bitmap graphics in their projects.

So how does the Flash designer decide what type of images to use in a project? If you take a closer look at these new and improved ecards, you will notice that vector graphics are still the favorite for complex animations that require the animated object to change size, shape or color. But the background of the animation scene is no longer always a vector based gradient or drawing. Those boring backgrounds are being replaced with more interesting bitmap graphics that add much to the look and feel of the ecard and to the story being told by the animation. Also, bitmap objects are being used more frequently in animations that require the object to only move around the stage but not change its shape or color.

If you decide to use bitmaps in your Flash project, there are a few things you can do to keep the file size from growing too large. One reason that bitmaps have gotten a bad reputation with Flash designers in the past is that they increase the workload on the Flash Player. Basically, when the Flash Player plays a Flash movie, it continuously redraws everything on the stage. It takes less work for the Flash Player to draw or redraw a vector graphic as compared to a raster graphic. So, one way to make life easier for your Flash Player is to tell it which raster images don't need to be redrawn because they stay the same throughout the movie, or section of the movie. A good example for this technique is the background raster graphic that does not change over time. We can do this with Runtime Bitmap Caching. Basically, we tell Flash to take a picture of the current background and use that same image for the background until we tell it otherwise. Another way to reduce file size is to optimized your raster images as much as possible. With each upgrade in Flash and the Flash Player, the way images are optimized by Flash has improved greatly. However, sometimes you can still save a few more KBs by customizing Flash’s JPEG quality settings.


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