2.2.2. Non integer downsampling factor¶

Sirius way to handle non integer downsampling factor consists in two step :

Upsampling to a common sampling grid (between input and output sampling grids)
Decimating to the output sampling grid

To illustrate this, say the input spacing is ${in}_{s}$ and output one is ${out}_{s}$ with ${out}_{s} > {in}_{s}, \frac{{out}_{s}}{{in}_{s}} \notin \mathbb N^{*}$ , then the downsampling factor deduced by Sirius is $z_{down} = \frac{p}{q} = \frac{{out}_{s}}{{in}_{s}}$ with $(p,q) \in \mathbb N^{*2}$ . The first step is then to upsample the input signal by a factor $q$ . Then, the output is decimated so that only $1$ pixel out of $p$ is kept.