A technique used to approximate halftones without reducing spatial resolution…

Answer: Dithering

Explanation: Dithering approximates continuous tones by arranging pixels or dots so that the human eye perceives intermediate shades. It does this through local patterns of light and dark pixels instead of reducing the image's spatial resolution.

• How it preserves resolution: rather than merging or enlarging dots (which lowers apparent resolution), dithering varies pixel placement and patterns, keeping high-frequency detail intact.

• Common methods: error-diffusion algorithms (for example, Floyd–Steinberg) are specific types of dithering that distribute quantization error to neighboring pixels for smoother tone reproduction.

• Why other choices are not the best answer: halftoning is a general term for representing tones with dots (and some halftone approaches can reduce apparent resolution), error diffusion is a particular dithering technique, and 'None of the above' is incorrect because dithering is the appropriate technique.