What is the different between image format JPG and GIF?

Answer 1

The difference in image types is the result of the need for compression. By default, most images have a fairly large file size, which is not conducive to use on the web. The most commonly compressed image file types are .jpg, .gif and .png.

The JPG file format, short for Joint Photographic Experts Group, is a type of image compression that works best with photographs and complex images. JPGs use a compression method that removes non-human-visibile colors from images to decrease file sizes. Be careful, though. If you decrease the quality of a JPG too much, you will begin to lose important color information that cannot be recovered. JPEG is a standardised image compression mechanism. JPEG is designed for compressing either full-colour (24 bit) or grey-scale digital images of "natural" (real-world) scenes.

A GIF, or a Graphics Interchange Format, reduces the number of colors in an image to 256, from potentially thousands of colors coming from a digital camera. GIFs also support transparency.

JPEG has a hard time with very sharp edges: a row of pure-black pixels adjacent to a row of pure-white pixels, for example. Sharp edges tend to come out blurred unless you use a very high quality setting. Edges this sharp are rare in scanned photographs, but are fairly common in GIF files: borders, overlaid text, etc. The blurriness is particularly objectionable with text that's only a few pixels high. If you have a GIF with a lot of small-size overlaid text, don't JPEG it.

Plain black-and-white (two level) images should never be converted to JPEG; they violate all of the conditions given above. You need at least about 16 grey levels before JPEG is useful for grey-scale images. It should also be noted that GIF is lossless for grey-scale images of up to 256 levels, while JPEG is not.