File Extension JPG
File extension JPG is used by
The compression is lossy meaning that original image is not represented with 100% accuracy. JPEG compression works best on real world images where color and luminance changes smoothly across the picture (without sharp edges). Sharp edges usually cause "compression artifacts". Compression artifacts are forms that are not present on the original uncompressed image. They are usually visible as small dots and lines next to the sharp edges. Amount and severity of artifacts depends on the compression ratio (or quality setting) that is chosen when image is compressed. Usually smaller resulting images causes more artifacts. It's important to note that even at maximum quality setting JPEG will product some artifacts.
JPEG files also contain image metadata in a form of EXIF tags. These tags contain data about image title, creation date, camera shooting conditions such as aperture, shutter speed, focusing distance etc. Recently it has become popular to "geo-tag" images - tag image with latitude and longitude of the shooting location. This can be done either by post-processing or by digital cameras that have GPS device built it.
JPEG images may have color-space information embedded in them in a form of ICM profile. This data is used by devices such as monitors and printers to correctly display color tones on the picture. Not all software supports or correctly processes color profile inormation. If no colorspace definition is present sRGB is usually assumed by default.
There are many applications that support viewing and editing JPG files. Besides native support by almost all modern operating systems these include: AcdSee, Paint.NET, Adobe Photoshop etc.