Reduce rounding error on coordinates in transform

[mortenwehlast]

Current implementation found to map 2D key points with error margin. Testing e.g. found that the point (0, 0) is mapped to (3, 3). Generally, absolute error falls in range [0; 3]. Proposed change reduces range to [0; 1]. Removing rounding + conversion to int eliminates error completely, but side effect on function "crop()" which uses "transform()" not tested. Hence, this solution appears more robust until testing on "crop()" is done.