Lightness Perception Model for Natural Images

A perceptual lightness anchoring model based on visual cognition is proposed. It can recover absolute lightness of natural images using filling-in mechanism from single-scale boundaries. First, it adapts the response of retinal photoreceptors to varying levels of illumination. Then luminance-correlated contrast information can be obtained through multiplex encoding without additional luminance channel. Dynamic normalization is used to get smooth and continuous boundary contours. Different boundaries are used for ON and OFF channel diffusion layers. Theoretical analysis and simulation results indicate that the model could recover natural images under varying illumination, and solve the trapping, blurring and fogging problems to some extent.

Experimental and simulation study on luminous characteristics of Trichel discharge in air at picosecond time resolution

The optical morphology of discharge is the main characteristic parameter describing the physical process of the discharge,and the luminescence behavior is inextricably linked to the motion behavior of charged particles.Since the Trichel discharge in air is a weak ionization event occurring on the sub-nanosecond time scale,micron space scale and accompanied by weak luminescence,the current experimental observation means have a low spatial and temporal resolution,which is insufficient to study the details of its luminescence properties clearly.To address this problem,the intensity of light generated by Trichel discharge in air is first measured and resolved in time and space using a constructed ultrafast optical counting and imaging system.At a very high temporal resolution of 55 ps,it is found that both its light emission and current pulse showed a trend of first rapid growth and then slow decline on the time scale of tens of nanoseconds.Later,in order to further investigate the connection between the microscopic behavior of charged particles and photons,a two-dimensional hydrodynamic simulation model with three components(electrons,positive ions,and negative ions)is developed and the current simulation results are in good agreement with the experimental results.The results show that the size of the ionization region and the interaction between particles in the discharge process are the main factors affecting the Trichel pulse and its photoemission.Electrons play a dominant role in photon generation during the rise time process,while it is the recombination process of positive and negative charges,which contributes the main photons during the fall time process.Finally,it is proposed that the expression of photon flux should be amended to include an additional term responsible for the photons generated due to recombination.The study helps to advance the understanding of the luminescence characteristics and the discharge mechanism of Trichel discharge.

Experimental research on the influence of temperature on the discharge signal of void defects in GIS

Temperature is an important environmental factor during the operation of gas‐insulated switchgear(GIS),affecting the evaluation results of the GIS equipment to increase the risk of the power system.However,the influence of temperature on the partial discharge detection signal of GIS is still unclear.Aimed at the common void defects in GIS,the law of change on the number of ultrahigh‐frequency(UHF)pulses,the UHF amplitude,the characteristic value of the UHF map,and the maximum apparent charge of a single pulse with temperature are obtained using the UHF method and IEC60270,and corresponding theoretical analysis is carried out.The results show that an increase in temperature leads to a decrease in the void discharge delay time,causing an increase in UHF pulses and a decrease in the apparent charge of a single discharge pulse in the experiment.The in-crease of temperature makes the void discharge current rise quickly so that the induced UHF amplitude increases.In the range of 40-70℃,the maximum pulse amplitude in-creases by approximately 30%for every 10℃ increase,and the average pulse amplitude increases by approximately 12%.The result of UHF signals affected by temperature obtained in this study has research significance for the realisation of a comprehensive evaluation of the insulation state of GIS equipment considering temperature.