In this scheme, the quantized DC
coefficients were used to conceal the watermark.
After zigzag scanning the coefficients in each block, the quantized DC
coefficients are encoded by differential pulse code modulation (DPCM), and the quantized AC coefficients are encoded by run length coding (RLC).
Because the 8 x 8 blocks are usually with strong correlation, the quantized DC
coefficient is encoded as the difference from the DC term of the previous block.
By applying quantization, we can use only [[log.sub.2](2040/Q)] bits to represent the quantized DC
Then in 1977, Levinson (49) showed that unbiased Josephson junctions would spontaneously develop quantized dc
voltages when irradiated with microwaves, opening the path to successful Josephson junction arrays.
Because there is usually strong correlation between the DC coefficients of adjacent 8 x 8 blocks, the quantized DC
coefficient is encoded as the difference from the DC term of the previous block in the encoding order (defined in the following), as shown in Figure 3.
After block DCT and quantization, the quantized DC coefficients carry the most important information of every 8 * 8 block.
A spatial temporal-chaos system was utilized to diffuse the quantized DC coefficients .
Similarly coding process is performed on the difference of quantized DC (DQDC) coefficients from neighbor blocks.
For the i-th element of quantized DC and non-zero AC coefficient [Q.sub.i], find its category [G.sub.i] according to Table 1.
The first one is that the proposed scheme encrypts quantized DC coefficients.
The second one is that the shuffle will destroy the correlation of quantized DC from neighbor blocks.