questions","basePath":"/gcse/computer-science/aqa/data-compression/questions","formulaUrl":null,"initialIndex":26,"initialQuestionWindow":[{"id":"60d53960-4fae-4a3f-b267-181d7a7a84bc","revisionId":"48b2e33f-78fd-4c1e-94ca-aa9e879e4e61","questionNumber":null,"questionType":"LA","specification":"A sequence of characters from the phrase *\"A CAFE BED\"* was encoded using the Huffman tree shown below.\n\n![Huffman tree for A, B, C, D, E, F and SPACE](https://assets.mathsgenie.co.uk/aqa-qb/2078b8af-980c-4ad7-aa4d-1a9cc63158c9.png)","difficulty":3,"difficultyBand":"easy","totalMarks":1,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"5d2d9ae4-99c5-4709-9ba8-e2bbfbf1cbe0","label":null,"content":"What string does the binary sequence `100111011110101` represent?","markscheme":"- Correctly decodes the binary sequence to **DECAF** (by matching `100` $\\rightarrow$ D, `111` $\\rightarrow$ E, `011` $\\rightarrow$ C, `110` $\\rightarrow$ A, `101` $\\rightarrow$ F) B1","marks":1,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"6223edf7-16fe-46d8-b488-788bdb3d0bff","revisionId":"781a90f8-65f1-422f-b785-63579a92bfd1","questionNumber":null,"questionType":"LA","specification":"Figure 2 shows a sequence of pixel values representing a single row of a black-and-white grid image:\n\n`B W B W B W B W`\n\n*(Where B = Black, W = White)*","difficulty":4,"difficultyBand":"easy","totalMarks":2,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"abe73940-9ee8-4e2a-8118-bd554b85b562","label":null,"content":"Explain why Run-Length Encoding (RLE) is **not** a suitable method for compressing this image row.","markscheme":"- Identifies that there are no consecutive repeating pixels or runs of the same colour in the sequence (the pattern alternates every pixel) B1\n- Explains that storing a frequency count of 1 for each alternating pixel (e.g. `1B 1W 1B 1W...`) introduces metadata overhead, making the encoded data larger than the original sequence B1","marks":2,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"66308f2d-056a-4bfa-ac70-4d1a03b4b555","revisionId":"3c98e71a-6441-487f-af22-39bd46f99ab0","questionNumber":null,"questionType":"LA","specification":"","difficulty":3,"difficultyBand":"easy","totalMarks":2,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"d23a4177-e830-4163-bdd1-78cf4c226b19","label":null,"content":"When a Huffman tree is used, the string in Figure 1 can be represented using 138 bits.\n\n### Figure 1\n`ARTIFICIAL INTELLIGENCE ALGORITHM`\n\nThe 33-character string shown in Figure 1 could also be encoded using standard 8-bit ASCII.\n\nHow many bits are saved when Huffman coding is used rather than ASCII to represent the string shown in Figure 1?\n\nYou must show your working.","markscheme":"- Calculates the ASCII bit size correctly by multiplying 33 characters by 8 bits to get $264$ bits M1\n- Subtracts 138 bits from their calculated ASCII bit size to find a saving of $126$ bits (or correctly subtracts 138 from an incorrect ASCII product) A1","marks":2,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null}],"subjectCode":"gcse_computer_science__aqa","summaries":[{"id":"01aceeda-575c-4ced-bc96-ba092de79c7e","difficultyBand":"medium","calculatorUse":null},{"id":"03fe5cea-6efd-45d9-aa60-75964ab4705a","difficultyBand":"easy","calculatorUse":null},{"id":"07d36a1a-5c14-476d-80ea-f2079e422bfb","difficultyBand":"easy","calculatorUse":null},{"id":"0ab264e5-e293-4736-91b6-fd500dfb6b02","difficultyBand":"easy","calculatorUse":null},{"id":"0fc37e4c-7cae-4c1a-9fb3-66f966107332","difficultyBand":"medium","calculatorUse":null},{"id":"1cb71686-bddf-4766-bac7-646e97cdb718","difficultyBand":"easy","calculatorUse":null},{"id":"1d080ea0-8d9f-41a4-ae48-50a80dde2388","difficultyBand":"medium","calculatorUse":null},{"id":"2388faa7-f

Data compression

Question 14

Data compression Questions

Data compression

Question 14

Data compression Questions