questions","basePath":"/gcse/computer-science/aqa/data-compression/questions","formulaUrl":null,"initialIndex":46,"initialQuestionWindow":[{"id":"bf35921d-00de-491a-84d3-15ed87ae7013","revisionId":"db95c910-66d2-4265-89a6-a4187622987f","questionNumber":null,"questionType":"LA","specification":"Figure 1 contains a Huffman tree used to encode text characters.\n\n![Huffman Tree](https://assets.mathsgenie.co.uk/aqa-qb/f234005d-6aac-4e6a-903a-bd2366083a6b.png)\n\n**Figure 1** was used to encode a string, resulting in the following bit pattern:\n\n`001010011`","difficulty":3,"difficultyBand":"easy","totalMarks":2,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"c87d68d2-1627-48c1-af30-505a7b53f261","label":null,"content":"State the string that this bit pattern represents.","markscheme":"- States the correct decoded string \"HERD\" A2\n- Award 1 mark if the final answer is incorrect but clear evidence of partial decoding is shown (e.g. correctly identifying the first two characters \"HE\", or indicating the correct boundaries in the bit pattern as `00 | 1 | 010 | 011`) M1","marks":2,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"c3517af4-72f1-4cb2-8f6e-344286f1a883","revisionId":"835b8d51-b3e1-4d3c-923f-688626db74da","questionNumber":null,"questionType":"LA","specification":"","difficulty":3,"difficultyBand":"easy","totalMarks":2,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"f5775879-5082-4384-a504-fc0f5fbc7b8f","label":null,"content":"Describe how Run-Length Encoding (RLE) is used to compress data. In your answer, you **must** include a short example showing a sequence of data before and after compression.","markscheme":"- Identifies sequences of consecutive or repeating data values (runs) and represents them as a frequency/count paired with the data value itself B1\n- Provides a correct, clear example showing a data sequence before and after compression (e.g. 'AAAAABBB' $\\rightarrow$ '5A3B') B1","marks":2,"order":0,"markingRubric":null,"explanation":null,"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"cb037db2-84dd-4458-bd05-f20aa6535aad","revisionId":"fa13c5f4-c7fe-42b7-9cba-2b3f1d08abcb","questionNumber":null,"questionType":"LA","specification":"A black and white image has been compressed using run-length encoding (RLE).\n\nEach run of pixels is encoded using a single byte (8 bits):\n* The first bit of each byte represents the colour: `0` for black, `1` for white.\n* The remaining seven bits represent the number of pixels in that run.\n\n**Figure 1** shows the bit pattern representing a run of 40 black pixels followed by a run of 75 white pixels.\n\nFigure 1\n| 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 1 |\n|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|","difficulty":4,"difficultyBand":"easy","totalMarks":2,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"c8bc0763-52ba-4a8c-b79c-6f5ab09cb434","label":null,"content":"Using the same RLE method, give the 16-bit pattern for a run of 18 white pixels followed by a run of 85 black pixels.\n\nWrite your answer in **Table 1**.\n\nTable 1\n| | | | | | | | | | | | | | | | |\n|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|","markscheme":"- Correctly encodes the first run (18 white pixels) as the byte `10010010` B1\n- Correctly encodes the second run (85 black pixels) as the byte `01010101` B1","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":"0ab264

Data compression

Question 32

Data compression Questions

Data compression

Question 32

Data compression Questions