1 Information representationAS Level

1.3 Compression

3 of 3 objectives have lessons · 0 studied · 0 secure

Lessons

Why compress? Smaller files, faster everythingWhy files are compressed (less storage, faster transmission, less bandwidth) and where you meet compression every day. 4 min, not started
Lossless vs lossy: keep everything, or keep enoughTell lossless compression, which restores the original exactly, from lossy compression, which removes some data for good, and name examples of each. 4 min, not started
Lossy or lossless? Justify your choiceChoose lossy or lossless compression for a situation and justify it by linking the choice to what the data is and how it will be used. 4 min, not started
Run-length encoding (RLE)Compress and decompress data with run-length encoding, work out the compressed size, and spot when RLE makes a file bigger instead of smaller. 5 min, not started
Compressing text: a dictionary of repeatsHow a text file is compressed losslessly by replacing repeated words or patterns with short references to a dictionary, and why RLE rarely helps with text. 4 min, not started
Compressing bitmaps with RLEApply run-length encoding to the pixels of a bitmap image, calculate the compressed size, and recognise which kinds of image RLE suits. 5 min, not started
Lossy image compression: lose what the eye won't missShrink a bitmap with lossy methods (lower resolution, lower colour depth, merging similar colours) and work out what each saves and costs. 5 min, not started
Compressing vector graphicsShrink a vector graphic by compressing its drawing list losslessly, or by simplifying paths and rounding coordinates (lossy). 4 min, not started
Compressing sound: cut what ears can't hearHow sound files are compressed, with lossy perceptual coding or lower sampling rates and resolutions, or with lossless methods that keep every sample. 5 min, not started

Syllabus objectives

3 objectives

What Cambridge says you should be able to do, in our words. Codes are the topic number plus the objective’s position.

1.3.1

Understand the need for compression and give examples of its use.

Taught in: Why compress? Smaller files, faster everything · 7 questions

1.3.2

Understand lossy and lossless compression, and justify the use of a method in a given situation.

Taught in: Lossy or lossless? Justify your choice, Lossless vs lossy: keep everything, or keep enough, Compressing sound: cut what ears can't hear · 12 questions

1.3.3

Understand how a text file, a bitmap image, a vector graphic and a sound file can be compressed.

Including the use of run-length encoding (RLE).

Taught in: Lossy image compression: lose what the eye won't miss, Compressing bitmaps with RLE, Run-length encoding (RLE), Compressing sound: cut what ears can't hear, Compressing text: a dictionary of repeats, Compressing vector graphics · 38 questions