how does text compression work

In this post we are going to explore LZ77, a lossless data-compression algorithm created by Lempel and Ziv in 1977. How Does It Work? Compression, however, isn’t a magic lozenge for curing a cramped hard drive. This gives JPEGs an insanely high compression ratio, which can reduce a file that would be multiple megabytes down to a couple of kilobytes, depending on the quality. Compression. Most pictures you see online are compressed to save on download times, especially for mobile users with poor data connections. This is mainly used for text and spreadsheets because losing words or data from a document isn't something you want to happen. Each time the image gets compressed, it loses some data.Here’s an example. Necessary when the source data is not plain text, say audio or video data. Where JPEG removes detail from an image that you won’t see, audio compression does the same for sounds. Processing power and storage space is very valuable on a computer. Windows Bitmap files (BMP) compress well. Nothing is lost. In reality, most text is compressed with keys as small as just a few characters. How does the ZIP format work? All Rights Reserved. Also, since interframe compression works best with mostly stationary video, this is why confetti ruins video quality. In general practice, you’ll probably get around 30-40% compression using a compression format like ZIP on a file that’s mostly text. When a request is made by a browser for a page from your site your webserver returns the smaller compressed file if the browser indicates that it understands the compression. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information that you’ve provided to them or that they’ve collected from your use of their services. And the more you compress, the more data you lose.This is what leads to those horrible-looking JPEGs that people have uploaded, shared, and screenshotted multiple times. Instead, it stores images using something called a Discrete Cosine Transform, which is a collection of sine waves added together at varying intensities. Compression Why compress files? Join 350,000 subscribers and get a daily digest of news, geek trivia, and our feature articles. Most of the files on your hard drive, however, are probably already in a compressed state. Interframe compression is the main reason we have digital TV and web video at all. Join 350,000 subscribers and get a daily digest of news, comics, trivia, reviews, and more. Other topics associated with compression include coding theory and statistical inference. Of course, if you use it too much, you end up with this: That image is horrible. These can be text files if they contain lots of spaces for indenting but line-art images that contain large white or black areas are far more suitable. Video and audio compression works very differently. ... then it adds the character to the current work string, and waits for the … MSc @ DTU. It was true when our hard drives were tiny, and the advent of the internet has just made it more critical. September 10th 2020 @dbudhraniDhanesh Budhrani. You consent to our cookies if you continue to use our website. So, for example, if you have a relatively still shot that takes up several seconds in a video, a lot of space gets saved because the compression algorithm doesn’t need to store all the stuff in the scene that doesn’t change. Now obviously, that’s a pretty extreme example since we just had the same word repeated over and over. Anthony Heddings is the resident cloud engineer for LifeSavvy Media, a technical writer, programmer, and an expert at Amazon's AWS platform. The original text file is three kilobytes in size. This is a screenshot I took that has not been compressed at all. If your bitrate is 200 kb/s, for example, your video will look pretty bad. These two algorithms are “LZ77” and “Huffman coding.” Huffman coding is quite complicated, and we won’t be going into detail on that one here. These areas of study were essentially created by Claude Shannon, who published fundamental papers on the topic in the late 1940s and early 1950s. There are also lossless compression codecs for audio—the main one being FLAC—which uses LZ77 encoding to deliver entirely lossless audio. RLE compression is only efficient with files that contain lots of repetitive data. Why are my digital photograph files so huge while photos on other Web sites are much smaller? How to Change the Theme and Accent Color of Instagram DMs, How to Record Shows and Movies on YouTube TV, How to Get Cycling Navigation Directions in Apple Maps. For now, we’re going to talk about the methods that are generally used to compress images, which will explain why some of them take up s… This algorithm is widely spread in our current systems since, for instance, ZIP and GZIP are based on LZ77. It seeks to remove duplicate words and replace them with a smaller “key” that represents the word. Most of the files on your hard drive, however, are probably already in a compressed state. Primarily, it uses some fancy math to assign shorter binary codes to individual letters, shrinking file sizes in the process. In more human terms, that means it decreases the size of your site’s files without changing any of their functionality. The most popular libraries for compressing text rely on two compression algorithms, using both at the same time to achieve very high compression ratios. In this post we are going to explore LZ77, a lossless data-compression algorithm created by Lempel and Ziv in 1977. This is what leads to those horrible-looking JPEGs that people have uploaded, shared, and screenshotted multiple times. However, lossless compression does not usually achieve the same file size reduction as lossy compression. We call compression like this “lossless”—the data you put in is the same as the data you get out. Currently @ Wubook. This algorithm is … RLE compression is only efficient with files that contain lots of repetitive data. Since we launched in 2006, our articles have been read more than 1 billion times. By submitting your email, you agree to the Terms of Use and Privacy Policy. Weird & Wacky, Copyright © 2020 HowStuffWorks, a division of InfoSpace Holdings, LLC, a System1 Company. 6 min read. In fact, all the images on How-To Geek have been compressed to make page loading quicker, and you probably never noticed. It uses 64 different equations, but most of these don’t get used. This demo does work better with actual video, so if you want to check it out for yourself, you can download the same bitrate test videos used here. Video and audio compression works very differently. Various lossless standards exist: PDF allows lossless compression of text documents JPEG does none of this. Each time the image gets compressed, it loses some data. For instance, using lossy compression on a text file or a spreadsheet would result in garbled output. But lossy compression doesn't work so well for files where all the information is crucial. Now, this is an idealized example. reactions. This LZ77 algorithm applies to all binary data, by the way, and not just text, though text generally is easier to compress due to how many repeated words most languages use. All modern browsers understand and accept compressed files. architectural drawings) can also give fair compression ratios. The PNG for this image was 200 KB in size, but this 50% quality JPEG is only 28 KB. Generally, YouTube videos sit around 2-10Mb/s depending on your connection, as anything more would probably not be noticed. Compression, however, isn’t a magic lozenge for curing a cramped hard drive. How does a zip drive store so much more data than a floppy drive? For example, text files can be smooshed down to become quite small.

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