depth</dd>
     <dd><samp>extent</samp>: image extent</dd>
     <dd><samp>minima</samp>: image minima</dd>
     <dd><samp>maxima</samp>: image maxima</dd>
     <dd><samp>mean</samp>: image mean</dd>
     <dd><samp>median</samp>: image median</dd>
     <dd><samp>standard_deviation</samp>: image standard deviation</dd>
     <dd><samp>kurtosis</samp>: image kurtosis</dd>
     <dd><samp>skewness</samp>: image skewness (add a channel specifier to compute a statistic for that channel, e.g. depth.r)</dd></dl></dd>