Noise is added to the image in the following way:

Noise Pixels

The collection of noise pixels for each band was taken from an image from the collection which had the most noise in its image.

Scaling the Noise

For this process the signal to noise ratio is defined as:

In my experiments this seemed to work the best. The signal to noise values for a single image are drawn at random and these are used to scale the noise so that the ratio holds for our synthetic image.

Example

h h

j j

v v

z z