Chapter intro: Images, sound and compression

The last chapter put text into binary, one code for every letter. Pictures and sound are harder, because neither one starts out as a list of anything. This chapter turns both into binary, works out how much room they take, and then makes them smaller. Here's where the marks sit, and which video to press first.

If this is all new, start with how an image is stored. Everything rests on two settings there: how many pixels, and how many bits each pixel gets. Examiners on every board report students mixing those two up.

Next comes turning a row of bits into a bitmap, which is the picture as a grid of coloured squares, and back again, by hand. Only one board sets it, and the video says so at the start. If pictures are fine and it's sound you're unsure of, go straight to how sound is stored. It's two settings again: how often the sound is measured, and how many bits each measurement gets. Boards use different names for that second setting, so learn the one your own board uses. If your exam is close, press working out image and sound file sizes. It's the same method you used for text in the last chapter, with the first step swapped, and the working you show carries most of the marks. The last part of the chapter starts with why we compress data, which every board sets. After that the boards split. Most ask about lossy and lossless compression, and one asks for two named methods instead, Huffman coding and run length encoding, with a video each. Every code on the list is a search term. Type it, or the title, and the video comes up, and the quickest place to search is the scholafly.com website, which indexes every video in every subject.

Next in the chapter is How an image is stored. Hopefully that's next in your feed - but if not, search for ScholaFly C S oh three, oh one.

For more, visit scholafly.com, or watch the next video.