- Noise is Nice -
... well at least grain is ...
I recently scanned some old and grainy analog prints, and was pleasantly surprised by the overall appeal of the images, despite the high compression (see file sizes).
Scan overview (2.7 MB original for 6802 by 4676 pixels = 31.8 MP)
Scan detail (400 by 600 pixels = 0.24 MP)
I found out that this is due to the fact that noise (oops, grain) helps to preserve colour accuracy by reducing the effect posterisation can have. Indeed, noise turns zones of equal colours into sets of differently couloured particles, which actively describe the colour they came from. Whilst posterisation may ruin the original colour, the noisy sets of particles appear to be rather immune to the phenomenon. Indeed, despite the fact that the individual particles change colour too, they keep on describing the average colour quite accurately when joined together. This particulary helps maintaining smooth and gradual transitions.
A Simple Test
Given the description above, the following test should be rather self-explanatory... at least I hope so ;-) And isn't it amazing ? The results even suggest that deliberately adding noise before going through a posterizing step could be a wise thing to do !