2.png is a bitmap format using lossless compression algorithm. Its design purpose is to try to replace GIF and TIFF file formats and add some functions that GIF file formats do not have. JPEG is a compression standard for continuous-tone still images. JPEG format is the most commonly used image file format, and the suffix is. Jpg or. jpeg。

3.JPEG mainly uses predictive coding (DPCM), discrete cosine transform (DCT) and entropy coding to remove redundant image and color data, which is a lossy compression format. It can compress the image in a very small storage space, which will destroy the image data to a certain extent. Especially, using too high compression ratio will reduce the quality of the restored image after final decompression. If you pursue high-quality images, you should not use too high compression ratio.