How to transform double integral into a single integral using diamond transform

I have a double integral given as,

$\displaystyle \frac{1}{T^{2}}\int_{-\frac{T}{2}}^{\frac{T}{2}}\int_{-\frac{T}{2}}^{\frac{T}{2}}\rho(t_{2}-t_{1})dt_{1}dt_{2}$ and I would like to convert it into a single integral as $\displaystyle \frac{2}{T}\int_{0}^{T}\left(1-\frac{\tau}{T}\right)\rho(\tau)d\tau$, where $\displaystyle \tau = t_{2}-t_{1}$. I read in the book that diamond transform is used to convert the given double integral into the single integral but am unable to understand it, since no elaboration is given. Can someone help me to understand how this double integral is transformed to the single integral as given above?

Thanks,

Ameya

Re: How to transform double integral into a single integral using diamond transform

Can someone explain how is 1-u/2 found?

Re: How to transform double integral into a single integral using diamond transform