An intelligence enhancement method for USV navigation visual measurement based on variable gradient soft-threshold correction

•This paper proposed a variable gradient soft-threshold correction (VGSC) algorithm.•We proposed a pixel dynamic equalization function to adjustment pixel-threshold.•The VGSC is verified to be effectively used in maritime image enhancement.•The VGSC can be applied to intelligent USV visual measurement, etc. Maritime image enhancement is crucial in marine engineering for applications like unmanned surface vessels (USV) visual measurement and path planning. This paper proposes an image enhancement algorithm based on variable gradient soft-threshold correction (VGSC), tailored for USV intelligent navigation. By calculating the gradient of the two-dimensional difference quotient function of the pixels, we determine the pixel distribution and threshold. An innovative dynamic equalization function is applied to compress maximum pixel values and stretch minimum ones, allowing for adaptive adjustment of the threshold. The results indicate that the VGSC algorithm effectively suppresses background noise, thereby facilitating the extraction of target contour pixel information. When evaluated using four image assessment indicators, the VGSC algorithm enhances the image quality by 20.09 % and 28.92 % compared to bilateral filtering and Gamma correction, respectively. This method excels in enhancing image details and suppressing noise, promising robust application in multi-modal data fusion and precise maritime target detection.