Post by juju on Apr 4, 2006 4:10:01 GMT -5
Joint Photographic Experts Group (JPEG)
(Pronounced JAY-peg.) The JPEG organization established standards for the JPEG file format, which is identified by the file extension .JPG.
JPEG images are frequently used on the World Wide Web because JPEG technology can reduce the size of a photo image file to as little as 5% of its original size. That 20-to-1 reduction translates into a 20-to-1 reduction in the time it takes to download an image from a Web server to your computer.
JPEG works by taking advantage of the way the human eye and mind perceive images. For example, we are less likely to note differences in colors than to note differences in brightness. A JPEG file exploits this foible by using the same color to describe two adjacent pixels, the tiny dots that make up computer images, whose colors differ only slightly.
Throwing out these odd bits and pieces makes JPEG a lossy compression method, meaning that some detail is lost when an image is saved as a JPEG file. The amount of detail that is lost can vary from little or no perceptible loss to a dramatic loss. Graphics programs can control the amount of detail preserved by a JPEG file—some use a sliding scale of 50 to 100 to represent low and high resolution, while others let you actually determine the number of dots per inch (dpi) in the image.
Of course, the more detail saved, the larger the file. You can save a great deal of space by saving a JPEG at a low quality if the image will be used primarily on a Web page. The typical computer monitor can’t display more than 72dpi of resolution anyway. You’ll need to save the JPEG at high quality if your objective is to transmit a photograph that will be used in a publication or brochure. Most publications require at least 300dpi for color photos; some may require as much as 2,500dpi.
The degree to which a JPEG file can be enlarged depends on its original quality. If your objective is to maintain every last detail of an image, you may want to save an image in the TIFF (Tagged Image File Format) or another lossless file format. JPEG also does not do a good job with line drawings, cartoons, text, and other simple black-and-white images with sharp lines of contrast.
JPEG is used only for still images, but a similar image file format, MPEG (Moving Pictures Experts Group), is used for video.
(Pronounced JAY-peg.) The JPEG organization established standards for the JPEG file format, which is identified by the file extension .JPG.
JPEG images are frequently used on the World Wide Web because JPEG technology can reduce the size of a photo image file to as little as 5% of its original size. That 20-to-1 reduction translates into a 20-to-1 reduction in the time it takes to download an image from a Web server to your computer.
JPEG works by taking advantage of the way the human eye and mind perceive images. For example, we are less likely to note differences in colors than to note differences in brightness. A JPEG file exploits this foible by using the same color to describe two adjacent pixels, the tiny dots that make up computer images, whose colors differ only slightly.
Throwing out these odd bits and pieces makes JPEG a lossy compression method, meaning that some detail is lost when an image is saved as a JPEG file. The amount of detail that is lost can vary from little or no perceptible loss to a dramatic loss. Graphics programs can control the amount of detail preserved by a JPEG file—some use a sliding scale of 50 to 100 to represent low and high resolution, while others let you actually determine the number of dots per inch (dpi) in the image.
Of course, the more detail saved, the larger the file. You can save a great deal of space by saving a JPEG at a low quality if the image will be used primarily on a Web page. The typical computer monitor can’t display more than 72dpi of resolution anyway. You’ll need to save the JPEG at high quality if your objective is to transmit a photograph that will be used in a publication or brochure. Most publications require at least 300dpi for color photos; some may require as much as 2,500dpi.
The degree to which a JPEG file can be enlarged depends on its original quality. If your objective is to maintain every last detail of an image, you may want to save an image in the TIFF (Tagged Image File Format) or another lossless file format. JPEG also does not do a good job with line drawings, cartoons, text, and other simple black-and-white images with sharp lines of contrast.
JPEG is used only for still images, but a similar image file format, MPEG (Moving Pictures Experts Group), is used for video.