I begin to study how codec works, and I found a "summary-diagram" for DCT-codec (DCT stands for Discrete Cosine Transform). On this diagram, there are of course two steps: the encoding step and the decoding one. I try to make a reproduction of this diagram herebelow:
ENCODING STEP Image (8*8 blocks) -->| FDCT |-->| Quantizer |-->| Entropy Encoder |--> Compressed data
DECODING STEP Compressed data -->| Entropy Decoder |-->| Dequantizer |-->| IDCT |--> Image (8*8 blocks)
The diagram seems clear to me, except the "Dequantizer". I don't understand how the quantification step can be reversed, since it is this step that causes information loss. What does this "block" do? Can someone give me more precisions?