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Example of noise 
of 
, 
, the correlation kernel 
where 
is produced by 
and 
, and the corresponding PSD 
. For the kernel, 50%-gray pixel color in the figure corresponds to value 0 in the data; for the PSD, black is 0. Note the missing low frequencies at the center of the PSD, and the higher-frequency nature of compared with the white streak noise η in Figure 1 ▸.
