Image Noises

By finding the signal-to-noise ratio we can evaluate the tolerance of the scanner’s electronics to various kinds of interference. Noise can be random or correlated, and we will deal with each type of noise independently.

Random Noise

The graphs below show the dependence of the random noise value on the reflection power of the grayscale sectors of the KODAK IT8.7/2 Q-60R2 target.

The signal-to-noise ratio, which is the ratio of the median of a grayscale sector to the deviation, should be regarded as “bigger is better”. That is, the bigger the SNR, the higher the scanner’s noise tolerance is. The delta SNR parameter is the total of the measurements.

As you see, although the scanners have the same stuffing, the experimental data are different. I’m inclined to write this discrepancy off to the irregularity of the scanners’ lamps, though – that’s a common thing with mercury-based fluorescent lamps.

Correlated Noise

Correlated forms of noise are the most annoying – they show themselves in the scanned image as regular “patterns” (usually horizontal or vertical stripes). The predominance of such noise greatly reduces the signal-to-noise coefficient, which is calculated as the ratio of the median to the deviation. The calculated coefficients are put into the next diagram. Bigger values are better: