Spot Noise is a texture synthesis technique, which in scientific visualization is used for vector field visualization. Image 7 shows that spot noise can also be used for tensor field visualization by visualizing the underlying vector field.
De Leeuw and van Wijk produce spot noise by drawing and blending together spots of random intensity at random position on a plane. The spots are bend and scaled according to the velocity magnitude. A zero velocity results in a round spot and a high velocity in a thin, usually bend, spot. The authors high-pass filter the spots to remove low frequency components in order to makes details in the texture standing out more clearly.
The above image shows a flow over a backward facing step, with pressure mapped to color. Note that spot bending is necessary in order to show the main flow and the turbulences behind the step.