Macromedia Flash 8 Bible

Preparing Bitmaps for Use in Flash 8

Regardless of the specific effects that you apply to your images in other programs, the key features to consider when preparing bitmaps for use in Flash are size, compression, and transparency.

• Size: It is important to know what the maximum image size will be in your final Flash layout. You may choose to size your bitmaps slightly larger than the final size to accommodate browser scaling. Although you can scale multiple instances of the same image to different sizes in Flash, if you intend to use many smaller thumbnails and only a single instance of the image at a larger size, it will be worthwhile to make a smaller copy of your image to import into Flash in addition to the original, larger image.

• Compression: Different compression schemes will work better on some images than on others. With experience, you will learn to select the most appropriate compression to maximize the quality of your images, while minimizing file size. For example, if you are working with a black-and-white photo that has high contrast or a bitmap image of a line-art illustration, you might find that GIF compression is actually more effective than JPEG compression.

  Some images need to be very high-resolution to maintain details, while other images (such as abstract background images) can be down-sampled significantly, while still serving their purpose in your design. Although you can always add additional compression to your images in Flash with the native JPEG options, it is helpful to decide on a baseline for an image and reduce it to the highest quality that you will actually need in your final presentation. If you choose to add JPEG compression to your images before importing them to Flash, open the Bitmap Properties dialog box to ensure that the Use Imported JPEG data option was applied when you imported the files to Flash. The Launch and Edit functionality of Fireworks ensures that you will always have the option to make changes to your source image, even if you use a flattened JPEG version of the image for authoring in Flash.

• Transparency: There are many different ways of adding transparency (or Alpha) to an image; you might need a very subtle fade of one image over another, or you might simply need to eliminate the white space around a central image. Deciding on the final effect that you need and then finding the best way to achieve this while keeping your file size small is the challenge. Bitmap file formats that support true transparency in Flash include PNG, PICT (Mac), BMP (Win), PSD, and TIFF. These file formats all have lossless native compression schemes, making them ideal for high-quality images. However, these benefits come with a high price in terms of file size. If you can achieve the effect that you need by applying a vector mask in Flash, or by cropping the original image, it is much better to take that approach.