The decoding keys include (i) the four middle frequency coefficients, (ii) two random permutation vectors, and (iii) a quantization
matrix for normalizing the watermark and the original image.
In this paper the histogram equalization and the successive mean quantization
transform methods for contrast enhancement of a low dynamic range image were evaluated and a comparison with an HDR- camera was shown.
Piva shows that, the performance of STDM watermarking  in the presence of two important classes of non-additive attacks, such as the gain attack with noise addition, and the quantization
attack are evaluated.
After the abstracted quantization
processing and contour extraction, we overlap the extracted contour line with quantized image, and the color space of acquired image is converted from space to RGB space.
to select N colors / select reference points prioritize reference points for each reference point, starting with the highest priority, optimize transformed point using previously transformed points apply interpolation using transformed reference points Just like Kuhn et al.
We can further calculate Signal to Quantization
Noise Ratio- SQNR [dB] as SQNR = 10 log ([[sigma].sup.2]/D).
Although the database can retain as much information as possible, the quantization
process is not aimed for specific CMM, thus limitations may exist.
Most of the HVS based quantization
techniques for DCT are proposed for perceptually non-uniform and non-linear YCbCr color space and fixed block sizes.
The Huffman code [2, 14, 15] is chosen, since it provides compact codeword length, especially when dealing with low number of quantization
consists on keeping the low frequencies and zeroing the other entries.