The fast development of image encryption requires performance evaluation metrics. Traditional metrics like entropy do not consider the correlation between local pixel and its neighborhood. These metrics cannot estimate encryption based on image pixel coordinate permutation. A novel effectiveness evaluation metric is proposed in this paper to address the issue. The cipher text image is transformed to bit stream. Then, Poker Test is implemented. The proposed metric considers the neighbor correlations of image by neighborhood selection and clip scan. The randomness of the cipher text image is tested by calculating the chi-square test value. Experiment results verify the efficiency of the proposed metrics.
Porous Bi2O3–Bi2S3 composite sheets
were constructed through a combinational
of chemical bath deposition and hydrothermal reaction. The Na2S precursor concentration in the hydrothermal solution was
varied to understand the correlation between the vulcanization degree
and structure evolution of the porous Bi2O3–Bi2S3 composite sheets. The control of the etching
rate of the Bi2O3 sheet template and the regrowth
rate of Bi2S3 crystallites via suitable sulfide
precursor concentration during the hydrothermal reaction utilizes
the formation of porous Bi2O3–Bi2S3 sheets. Due to the presence of Bi2S3 crystallites and porous structure in the Bi2O3–Bi2S3 composites, the
improved visible-light absorption ability and separation efficiency
of photogenerated charge carriers are achieved. Furthermore, the as-synthesized
sheets obtained from vulcanization with a 0.01M Na2S precursor
display highly enhanced photocatalytic degradation toward methyl orange
(MO) dyes compared with the pristine Bi2O3 and
Bi2S3. The porous Bi2O3–Bi2S3 sheet system shows high surface
active sites, fast transfer, high-efficiency separation of photoinduced
charge carriers, and enhanced redox capacity concerning their constituent
counterparts. This study affords a promising approach to constructing
Bi2O3-based Z-scheme composites with a suitable
microstructure and Bi2O3/Bi2S3 phase ratio for photoactive device applications.
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