JPEG (
Joint Photographic Experts Group, the standards body that created the image format) is a lossy image compression
file format which offers a variety of quality levels and the image's file size are generally proportional. JPEG images inhabit the YUV color space, which uses brightness, hue, and saturation to represent an image.
SL
textures and
heightmaps use the
JPEG2000 format, which is actually altogether different from JPEG.
See also:
JPEG article at Wikipedia.