Week 3 Lesson Spec ref Lesson Lesson content Lesson summary resources 1 3.3.2 Compression: Start the lesson by recapping why files are compressed, i.e. to make them more Week 3 lossless run-length space-efficient and to enable them to be transferred quickly. If you feel students need Lesson 1 3.3.3 activities encoding more practice encoding or decompressing 4-bit colour images using RLE, you could select one student to read out their data (Lesson 1 homework activity) and ask the 3.3.4 Autumn term rest of the class to decode and draw the image. Alternatively, you could put students Year 11 into pairs and have them decode each other’s images. Some groups may need to Programming recap the data size units i.e. bits, bytes, MB. Solutions Use the 4-bit colour image in homework Activity 2.1.4 to walk students through how to calculate the size (in bytes) of the uncompressed and the compressed files, pointing out the small size reduction. Size of compressed file in bytes = number of codes x number of bits in each code / 8 = 84 x 6 / 8 = 63 bytes Size of uncompressed file in bytes = number of squares in grid x 2 / 8 = 256 x 2 / 8 = 64 bytes Explain to students the need to multiply the number of squares in the grid by 2 as each square in the grid is one of four colours, which is represented by a 2-bit number. Now give students the opportunity to do these calculations for themselves on the
Week 3 Lesson Spec ref Lesson summary Lesson content Lesson resources 1 3.3.2 3.3.3 3.3.4 Compression: lossless run-length encoding Start the lesson by recapping why files are compressed, i.e. to make them more space-efficient and to enable them to be transferred quickly. If you feel students need more practice encoding or decompressing 4-bit colour images using RLE, you could select one student to read out their data (Lesson 1 homework activity) and ask the rest of the class to decode and draw the image. Alternatively, you could put students into pairs and have them decode each other’s images. Some groups may need to recap the data size units i.e. bits, bytes, MB. Use the 4-bit colour image in homework Activity 2.1.4 to walk students through how to calculate the size (in bytes) of the uncompressed and the compressed files, pointing out the small size reduction. Size of compressed file in bytes = number of codes x number of bits in each code / 8 = 84 x 6 / 8 = 63 bytes Size of uncompressed file in bytes = number of squares in grid x 2 / 8 = 256 x 2 / 8 = 64 bytes Explain to students the need to multiply the number of squares in the grid by 2 as each square in the grid is one of four colours, which is represented by a 2-bit number. Now give students the opportunity to do these calculations for themselves on the Week 3 Lesson 1 activities Autumn term Year 11 Programming Solutions
gcse-cs-autumn-term-year-11-scheme-of-work.docx