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JPEG (Joint Photographic Experts Group) 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 (often 510 times) 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.
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24 เม.ย. 54 12:33:12
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