(3) JPEG image format
JPEG defines a common compression and encoding method for pictures and images. This is the best compression technique so far.
1. Introduction to JPEG Files JPEG (Joint Photographic Experts Group) is the first international digital image compression standard established by the International Standards Organization (ISO), the International Telegraph and Telegraph Consultative Committee (CCITT) and the International Electrotechnical Commission (IEC) for continuous tone still images. . The image file interaction format built on this compression standard is the JPEG image format.
2. Advantages of JPEG format application (1) Save storage space. The space saved by processing images by the JPEG compression method is numerous. For example, a true color image of 727 pixels * 525 pixels, the original 24-bit format for each pixel takes up 1145K, GIF format is 240K, very high quality JPEG format is 155K, and the standard JPEG format is only 58K, when When viewed on a monitor, the 58K JPEG image has the same quality as the GIF image format, and the 155K JPEG image is much better than the 256-color GIF image. When the compression ratio is not too large, the true color image (8 pixel x 8 pixel image unit) reconstructed by the JPEG decompression program is almost indistinguishable from the original image stored using one pixel multiplied by one pixel. , can browse display.
(2) Economical method of storing image data. The JPEG format is commonly used for displaying indexed color images in the form of hypertext markup language. It is widely used on the Internet and other online service systems like the GIF format, but the difference is that GIF converts RGB images to indexed color images. It can only retain up to 256 colors in the image, for which some colors need to be discarded. In contrast, JPEG retains all the colors in an RGB image. The addition of JPEG can compress image data in large amounts, and is therefore an economical method of storing image data.
It supports a variety of image types, including CMYK images, grayscale images, and RGB images.
3. Insufficient application of JPEG format (1) Color loss problem. JPEG removes the correlation between image lines and rows, columns, and columns. It is necessary to discard some data, so it is called lossy compression. The use of the JPEG method to compress images requires a trade-off between file size and color loss. In most cases, if a smaller compression ratio is used, the color change of the compressed image is difficult to distinguish. For example, if you use the Maximum option to compress an image in Photoshop, it is difficult for the average person to distinguish the compressed image from the original image after being expanded by a decompression program.
(2) Compatibility issues. Software compression and restore speeds are slow, format standards are still evolving, and because there are options in the standard, there are incompatibilities.
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