TPE-H2MWD:an exact thumbnail preserving encryption scheme with hidden Markov model and weighted diffusion

With the substantial increase in image transmission,the demand for image security is increasing.Noise-like images can be obtained by conventional encryption schemes,and although the security of the images can be guaranteed,the noise-like images cannot be directly previewed and retrieved.Based on the rank-then-encipher method,some researchers have designed a three-pixel exact thumbnail preserving encryption(TPE2)scheme,which can be applied to balance the security and availability of images,but this scheme has low encryption efficiency.In this paper,we introduce an efficient exact thumbnail preserving encryption scheme.First,blocking and bit-plane decomposition operations are performed on the plaintext image.The zigzag scrambling model is used to change the bit positions in the lower four bit planes.Subsequently,an operation is devised to permute the higher four bit planes,which is an extended application of the hidden Markov model.Finally,according to the difference in bit weights in each bit plane,a bit-level weighted diffusion rule is established to generate an encrypted image and still maintain the same sum of pixels within the block.Simulation results show that the proposed scheme improves the encryption efficiency and can guarantee the availability of images while protecting their privacy.

Effects of leaf response velocity on spray deposition with an air-assisted orchard sprayer

The interaction between leaves and airflow has a direct effect on the droplet deposition characteristics of the leaf canopy.In order to make clear the mechanism of droplet deposition in terms of the interaction between the droplets and leaves from the point of the leaf aerodynamic response velocity,the leaf movement under different airflow velocities and the influence of the leaf aerodynamic response on droplet coverage ratio were investigated.The effect of the aerodynamic response velocity of a leaf on the droplet deposition of the leaf surface was investigated.The aerodynamic characteristics of the leaf were analyzed theoretically.Boundary layer theory from fluid mechanics was used to develop a model of the leaf aerodynamic response velocity to nonperiodic excitations based on a convolution integral method.Target leaf aerodynamic velocities were detected using a high-speed camera,and the results indicated that the modeled leaf aerodynamic response velocity matched the measured values.At given conditions of spray liquid and leaf surface texture,the spray test showed that the droplet coverage ratio was influenced by the leaf aerodynamic response velocity,the droplet coverage ratio increased and then decreased with the leaf response velocity.Through analyze four droplets deposition state,the highest droplet deposition ratio and best deposition state on the leaf surface occur when the leaf aerodynamic response velocity was less than 0.14 m/s.According to the analysis of droplet deposition states,the uniformity of the droplet size and quantity distribution of droplets on the leaf surface related to the leaf aerodynamic response velocity.The results can provide a basis for the design and optimization of orchard air sprayers.