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Only available in some formats
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Transparent graphics allow background to show through part of image
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Animations allow simple moving images, e.g. cartoons
Certain image formats also support some more advanced features, such as transparency or animation. With transparency, parts of the image can be made transparent, giving the effect of a shaped image, or blending in with a background colour. In the GIF format, for example, a single colour value in the image may be marked as transparent, so that areas having this colour value will not be drawn on screen. More advanced, graduated, transparency effects are possible with the newer PNG format, using an alpha channel, which can create shadows that overlay the background beneath the image.
GIF animations can be a simple way to add cartoon-like movement to an image. Instead of storing a single image, they store a sequence of images along with a time delay; the images are displayed much like a flick-book cartoon. They should be used sparingly on web pages, as they can be distracting to the reader.
![[Note]](../images/note.gif)
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Which bitmap format? |
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GIF (Compuserve Graphics Interchange Format): Lossless, medium compression, up to 8-bit colour, supports single-colour transparency and animation; good for simple clip-art style graphics. Proprietary standard; some issues over copyright. JPEG (Joint Photographic Experts Group): Lossy, very high compression, 24-bit colour only. Excellent for
photographic images. Filename extension usually abbreviated to
PNG (Portable Network Graphic): Lossless, medium compression, up to 36-bit colour, with graduated transparency. Not supported by many older browsers. Designed as an open standard to replace GIF. TIFF (Tagged Image File Format): Lossless, with medium, low or no compression. Wide range of colour depths available. Used mainly for intermediate saving of images in progress, before final compression into JPEG. There are also numerous formats that are tied to particular graphics
packages, such as |