Q6 — Calculate uncompressed image file size (5 marks)

Question: A bitmap image is 800 pixels wide and 600 pixels tall, with a colour depth of 24 bits per pixel. (a) Calculate the file size of the image in megabytes (MB). Show your working. (3) (b) State one lossy and one lossless compression technique that could reduce this file size. (2)

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Mark scheme (5 marks): (a)

• 800 × 600 × 24 = 11,520,000 bits (1)
• ÷ 8 = 1,440,000 bytes (1)
• ÷ 1,000,000 = 1.44 MB (1) (OCR uses decimal prefixes; accept 1.44 MB or 1.37 MiB if explained)

(b)

• Lossy: JPEG (1)
• Lossless: PNG / Run-Length Encoding / Huffman coding (1)