The inter-picture prediction reduces temporal redundancy, with motion vectors used to compensate for motion. Whilst only integer-valued motion vectors are supported in H.261, a blurring filter can be applied to the prediction signal – partially mitigating the lack of fractional-sample motion vector precision. Transform coding using an 8×8 discrete cosine transform (DCT) reduces the spatial redundancy. The DCT that is widely used in this regard was introduced by N. Ahmed, T. Natarajan and K. R. Rao in 1974. Scalar quantization is then applied to round the transform coefficients to the appropriate precision determined by a step size control parameter, and the quantized transform coefficients are zig-zag scanned and entropy-coded (using a "run-level" variable-length code) to remove statistical redundancy.