graph of lowpass filter Check the equation 4.8-1 $H(u,v)=1$ if $D(u,v)\le D_0$

my question is the high frequency is at center.

$D(u,v)$ is smaller if it is close to center.

why $H(u,v)=1$ in that case.
Thanks
There is no high frequency in the center. In the center of your 2D spatial frequency distribution is the 0-frequency (constant DC component of the Fourier-transformation). The text excerpt is in itself consistent. Therefore I suppose you misunderstood the problem or the initial assumptions of its solution.