Question

Using rough rule of thumb, and assuming powers of 2 for convenience, what image size are about the smallest images that can be expected to be reasonably free of objectionable sampling checkerboards and false contouring?

(a) 512*512pixels and 16 gray levels

(b) 256*256pixels and 64 gray levels

(c) 64*64pixels and 16 gray levels

(d) 32*32pixels and 32 gray levels

This question was addressed to me during an interview for a job.

Asked question is from Spatial and Gray-Level Resolution and Aliasing in portion Image Enhancement of Digital Image Processing

Answer 1

Right choice is (b) 256*256pixels and 64 gray levels

To explain: An image of 128*128pixels shows a pronounced checkerboard pattern, while for 256*256pixels image a minimum gray level of 64 is required to remove false contouring.

Also the effect is quite visible in images displayed using 16 or less uniformly spaced gray levels.