file formats


Determining which format to use when saving an image is not as simple a task as it may seem. An understanding of the differences between the formats is needed in order to choose the one that will provide the best results. There are three web-ready formats to discuss.



After determining the number of colors necessary for an image, determine which colors should be used. Palettes are sets of colors the computer uses when saving an image to a GIF format. There are several different types:

bit depth


Bit depth is a term which essentially describes the amount of colors in a picture. (Note: The ability to control bit depth is only possible when exporting images to .gif and .png formats.) There is a close relationship between the amount of colors in an image and the size of the file.



Thinking about images in terms of inches doesn't really work for the web. Instead, people talk about images using a measurement called "pixels."

While working with graphics, define the image size in terms of the number of pixels. To make the jump from inches-based measurement to pixel-based measurement, look at the table below (based on 72 ppi images).



Resolution refers to the amount of space available to represent an image. The terms DPI (dots per inch) and PPI (pixels per inch) are used to describe the resolution of an image. The higher the resolution, the more space that is available to describe the content of the image. The more data, the larger the file size and the longer the download time for a user.

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