Reading 5 - Taoxi Li

       The article “On Compression” talked about the two ways that compression of data is achieved. The first kind is called Lossless compression, which keeps all information from input data and can be expanded later to reproduce the original input information. This method can keep all information intact and unchanged but cannot save space, and it is often used to compress text and data files. The second kind is Lossy, and it selectively leaves out some information when compressing, but it keeps enough amount of data that is needed to recreate images/video/audio files that look/sound good enough for viewers. Below are three images that use lossy compression at different level. Lower compression means higher quality and larger size. It is quite surprising to me that over 90% of the original information are lost yet the images are still recognizable—our eyes are so easily deceivable!

(Low compression : 84% less information than uncompressed PNG, 9.37 KB)

(Medium compression (92% less information than uncompressed PNG, 4.82 KB)

(High compression (98% less information than uncompressed PNG, 1.14 KB)

     This article also makes me think that compression is compromise between efficiency and quality. This decision happens very often in across internet today: whether it is emailing your friends a 3-minute video of your vacation or uploading an 2-hour film documentary for your portfolio, information is constantly being compressed and decompressed. In out class for example, I believe we mostly used the Lossless method to “zip” and uploaded our files to Google Drive and then downloaded and unzipped it to demonstrate in class, because we want the input information—the codes— to maintain unchanged. However, when making the video documentation and sharing them on YouTube/Vimeo, the video needs to be compressed to save space and also time for people to view it. I’m not sure if this is the reason why our video documentations sometimes look blurry and even fragmented. Video/image sharing websites should inform the authors how much information is maintained and how much is lost before they put their work to the public, since the quality of the video significantly affects the feel and look of the actual work. When uploading videos to websites, we should also consider how often they will be watched online and downloaded, because that affects whether we choose either the quality or efficiency of the file.

      According to the video above, compression methods also differ depending on what media is used to present information—images for print media are often saved with lossless compression because it’s much more important to keep the integrity of image than when it’s put on the internet. I also learned that the lossy compression is an irreversible process, so it’s important to keep the original work.