Today, smart phones and handheld games usually support the 16-bit color space. This palette is called high color and sports a grand total of 65,000 colors. Although this sounds like a lot, 16-bit color is not considered good enough for most graphic design purposes or professional printing. The highest color space is 24-bit color, which is called true color. This system generates up to 16.7 million colors. It is the gold standard for graphic design and professional printing. Several years ago a new color space was added to the mix: 32-bit color. It doesn’t offer any additional colors, but it provides an extra eight bits for an attribute called alpha transparency. Here you can see a dramatic comparison of three color-spaces and what the total number of available colors means to image quality.
24-bit color
8-bit color
4-bit color
Alpha transparency enables you to designate parts of graphics as fully or partially transparent, which allows you to create graphics that seem to have rounded corners or curves and eliminate the white bounding box typical of raster graphics. As with dimensions, color-depth can dramatically affect image file size. With all other aspects being equal, an 8-bit image is over 7 times larger than a monochrome image. And, the 24-bit version is over 3 times larger than the 8-bit image. The key to effective use of images on a website is finding the balance of resolution, size, and color to achieve the desired optimal quality.
Raster image file formats Raster images can be stored in a multitude of file formats, but web designers have to be concerned with only three: GIF, JPEG, and PNG. These three formats are optimized for the Internet and compatible with most browsers. However, they are not equal in capability.
GIF GIF (graphic interchange format) was one of the first raster image file formats designed specifically for the web. It has changed only a little in the last 20 years. GIF supports a maximum of 256 colors (8-bit palette) and 72 ppi, so it’s used mainly for web interfaces, buttons, graphical borders, and such. But it does have several interesting features that keep it pertinent for today’s web designers: index transparency and animation.
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