Do Now! Convert the following sequence of bits into an image using the protocol we discussed (first 8 bits are lengthxwidth, Then fill in the rows pixel by pixel, 1 = white, 0 = black) 0111010100010000111011011100001111100001000

CS Principles U2L5 Lossy Compression

U2L5 Lossy Compression Objectives SWBAT: Explain the difference between lossy and lossless compression. Identify common computer file types and whether they are compressed or not, and whether compression is lossy or lossless. Read a technical article on the web and sift its contents for targeted information.

U2L5 Vocab Lossless Compression - a data compression algorithm that allows the original data to be perfectly reconstructed from the compressed data. Lossy Compression - (or irreversible compression) a data compression method that uses inexact approximations, discarding some data to represent the content. Most commonly seen in image formats like .jpg.

U2L5 Content: Lossy vs Lossless Compression Lossy compression is mostly used in visual or audio formats where a loss in precision is undetectable to human eyes and ears. The BMP image format is basically the image encoding format used in code studio The GIF image format and ZIP compression scheme are versions of the text compression scheme we used as well. In the case of GIF, it uses a dictionary of up to 255 different colors and each pixel is stored as small number that refers to the dictionary

Lossy Text Compression App With a partner, go to the Lossy Text Compression App - App Lab. Answer the following questions: U2L5 Prompt: What is happening in the app? Should this “count” as text compression? Why or why not? What do you think “lossy” refers to?

Lossy vs LossLess When we did text compression a few lessons ago, that kind of compression is known as “lossless” compression because in doing the compression, and in reconstructing the original text, nothing was lost; every character that was part of the original text could be recovered. “Lossy” compression – yes, that’s the official word – does something else. Lossy compression schemes are ones in which “useless” or less-than-totally-necessary information is thrown out in order to reduce the size of the data. The lossy text compression app did that, and for the most part, you could probably make out what the text was supposed to say. But it’s not perfect. If you saw the word “fd” it could be “food”, “feed”, “feud”, or “fad”. By reading it in context, you might know what it was supposed to be, but there’s no real way to know what the original word was. The original word is lost.

Rapid Research Research your assigned topic with your partner. -Google your topic (topic + compression) -Find an appropriate page and fill in your row of the chart 10 MINUTES!

Jigsaw Form 3 groups, each with at least 1 member from each group. Share out your information with your group members. Information should be given orally; you should not be COPYING information from other people’s worksheets. 10 MINUTES

What did you learn? BMP- JPG- WAV- PNG- MP3- GIF- ZIP-