Converting an analog image to digital requires 2 independent choices.
- Pixelation (spatial resolution)
Determined by the size of the image sensor element. - Quantization (grey-level depth)
Determined by the resolution of the analog to digital converter.
Resolution is the number of samples per unit length. Grey-level depth is the number of discrete intensity levels. Both determine the memory required for image storage.
Sampling effects
- Loss of information
More apparent with large sampling regions and images with fine detail. - Aliasing
Occurs when the sampling interval differs slightly from signal frequencies.
Dithering
Used in 2-colour systems to create the impression of intermediate grey levels.
- Each sampled pixel is divided into several sub-pixels
- Pixel intensity is represented as a pattern within the sub-pixel region