[SFW] Random pics that make you laugh - Page 714

JPEG (Joint Photographic Experts Group) format can produce a smaller file than PNG for photographic (and photo-like) images, since JPEG uses a lossy encoding method specifically designed for photographic image data, which is typically dominated by soft, low-contrast transitions, and an amount of noise or similar irregular structures. Using PNG instead of a high-quality JPEG for such images would result in a large increase in filesize with negligible gain in quality. By contrast, when storing images that contain text, line art, or graphics – images with sharp transitions and large areas of solid color – the PNG format can compress image data more than JPEG can, and without the noticeable visual artifacts which JPEG produces around high-contrast areas. Where an image contains both sharp transitions and photographic parts a choice must be made between the two effects. Note that JPEG does not support transparency.

Because JPEG uses lossy compression, it suffers from generation loss, where repeatedly encoding and decoding an image progressively loses information and degrades the image. Because PNG is lossless, it is a suitable format for storing images to be edited. While PNG is reasonably efficient when compressing photographic images, there are lossless compression formats designed for specifically for photographic images, lossless JPEG 2000 and Adobe DNG (Digital negative) for example. However these format are either not widely supported or proprietary. An image can be saved into JPEG format for distribution so that the single pass of JPEG encoding will not noticeably degrade the image.