size(Residuals,1) is the number of rows in the Residuals array. 1:2:size(Residuals,1) is the odd-numbered rows. [1:2:size(Residuals,1)] in context is redundant and could be just 1:2:size(Residuals,1) .
So the odd-number rows are selected from Residuals, and the same numbering is used for the columns as well . That is a little risky unless Residuals is known to be the same number of rows and columns.
Channel is kept constant, a scalar, and used to index the third dimension.
All of the 4th dimension is selected.
So Newres in the third pane selected by Channel becomes the odd-numbered rows and columns of Residuals from the third pane selected by Channel.
