 Each 8×8 block is encoded by first applying a "forward" discrete cosine transform (FDCT) and then a quantization process.The FDCT process (by itself) is theoretically lossless, and can be reversed by applying an "Inverse" DCT (IDCT) to reproduce the original values (in the absence of any quantization and rounding errors).In reality, there are some (sometimes large) rounding errors introduced both by quantization in the encoder (as described in the next section) and by IDCT approximation error in the decoder.