Fair enough, maybe compression is a too specific term to apply here but I does not matter if it's compression or not to violate copyright. Compression was a good example to mention because it is already familiar to laypeople and established law. The main point is that it stores some sample of the original data - and if it's more it is derived from the original data (your strokes example) and applying some algorithm to reconstruct it to some approximation that we humans might find indistinguishable