An output rescale module may determine an estimated set of lines to hold in vertical support for use when performing image transformations. For example, an output rescale module may monitor input Y coordinates (in terms of input pixel lines) computed over previous lines and compute a set of lines to hold in a set of line buffers. As each output pixel line is generated, the output rescale module may compute the minimum and maximum values of Y generated by the transform across that line. The minimum and maximum input Y coordinates may then be averaged to determine the center value (the centermost input line) for that output line. The difference (in terms of input pixel lines) between centerlines for two adjacent output lines may be added to the centerline value for the current output line to estimate a center line for the next (not yet generated) output pixel line.