A Computational Introduction to Digital Image Processing, 2nd Edition

184 A Computational Introduction to Digital Image Processing, Second Edition

The reason is that

fspecial adjusts its output to keep the volume under the Gaussian

function always 1. This means that a wider function, with a large standard deviation, will

have a low maximum. So we need to scale the result so that the central value will be 1; and

mat2gray does that automatically.

The transforms are shown in Figure 7.24(a) and (c). In each case, the final parameter of

the

fspecial

function is the standard deviation; it controls the width of the filter. Clearly,

the larger the standard deviation, the wider the function, and so the greater amount of the

transform ...