Images: The effect of colour depth and resolution on:quality of the image, size of an image file

Colour depth and resolution are the two main factors that affect both the quality and file size of an image. Increasing either one improves quality but increases the file size.

Key points

• Increasing resolution = more pixels = higher quality (more detail) AND larger file size.
• Increasing colour depth = more bits per pixel = wider range of colours = higher quality AND larger file size.
• Image file size = colour depth x width (px) x height (px).
• Exam Tip:When asked about the EFFECT of increasing resolution or colour depth, always mention BOTH quality AND file size — they both increase.
• Common Mistake:Only discussing quality or only discussing file size. Examiners expect you to address both.
• Common Mistake:Saying higher colour depth gives 'higher resolution'. Colour depth and resolution are DIFFERENT things. Colour depth = bits per pixel. Resolution = number of pixels.
• Exam Tip:Maximum colours = 2^(colour depth). 4-bit = 16 colours, NOT 4. A common exam error is giving 4 colours for 4-bit depth.