In computing, JPG (pronounced JAY-peg) is a commonly used method of compression for photographic images. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality.
Less compression usually results in an image that cannot be distinguished by eye from the original. Extreme compression will look distinctly artifacted compared to the original. The appropriate level of compression depends on the use to which the image will be put as well as the nature of the image itself.
Those who use the World Wide Web may be familiar with the irregularities known as compression artifacts that appear in JPG images. These are due to the quantization step of the JPG algorithm. They are especially noticeable around text. They can be reduced by choosing a lower level of compression; they may be eliminated by saving an image using a lossless file format such as png, though for photographic images this will usually result in a larger file size. Compression artifacts make low-quality JPGs unacceptable for images with high pixel contrast (pixels change color greatly from one pixel to the next, such as with maps).
Some programs, such as (Wiki Swiss Tool), allow you to specify the quality of encoding (level of compression). This ranges from 1 (lowest quality) to 100 (highest quality). Higher quality means less compression so the file size will be larger. Generally values between 75 and 90 are used as a reasonable tradeoff between size and quality.