he decisions you make about file format, compression, palette, resolution, and bit depth effect both quality and download speeds.
There are a number of technical decisions you'll need to make as you create and optimize images for the web. Here are some of the decisions you'll need to make. Click on the option to learn more about it.
Graphics File Formats
GIF, JPEG, and PNG are three common graphic formats. Each has its best use.
- File Format. Make sure the format you select is the best match for each graphic.
- Bitmapped or Vector. Each type of defintion has its strengths.
- Resolution.The Web is not print. The Web is not print. The Web is not print.
- Indexed color. You can set the range of colors (the palette) for your graphic.
- Anti-aliasing. This technique makes bits appear smoother.
- Compression. The tradeoffs in making files even smaller.
- Thumbnails. A way to show large images in a smaller space.
Just as you can save text documents in different file formats, .txt (straight text), .doc (Microsoft Word), .rtf (rich-text format), etc. so too can you save graphic images in different formats. Each format is designed to handle a specific kind of image and applies a different type of compression to the image.
In this section, we'll show you how to choose the best file format for your Web-page images. With the right format, your images will look great and equally important on the Web your image files will be kept to a minimum.
The two main file formats used for Web images are GIF and JPEG. Both formats were developed long before the advent of the World Wide Web, but they really came into their own when they became the de facto standards for Web images.
- GIF works best with images composed of lines and solid blocks of color, such as text, cartoons, or buttons.
- JPEG works best with photographs and other continuous-tone images.
New image formats have been developed specifically for the Web. The one that has gained the most acceptance is PNG.
- PNG works equally well with either line or continuous tone image data.