Characters, Images and Sound

Characters

Text is stored using a character set mapping each character to a number:

• ASCII – 7 bits, 128 characters (English letters, digits, symbols).
• Extended ASCII – 8 bits, 256 characters.
• Unicode – up to 32 bits; covers every language and emoji.

Character codes are ordered: 'A' = 65, 'B' = 66 … 'a' = 97. So 'C' − 'A' = 2.

Images (bitmaps)

An image is a grid of pixels, each storing a colour in binary.

• Colour depth = bits per pixel → 2ⁿ colours.
• Resolution = width × height in pixels.

File size (bits) = width × height × colour depth

More bits / pixels = better quality but larger files. Add metadata (e.g. dimensions) for the full file size.

Sound

Analogue sound is sampled at regular intervals; each sample is stored in binary.

• Sample rate (Hz) = samples per second.
• Bit depth = bits per sample.

File size (bits) = sample rate × bit depth × seconds × channels

Higher sample rate / bit depth = closer to the original, bigger file.

Exam tip

Learn both file-size formulas — they appear most years. State that quality and file size both increase with more bits.