Adaptive Trigonometric Transformation Function With Image Contrast and Color Enhancement: Application to Unmanned Aerial System Imagery

Abstract

An unmanned aerial system (UAS)-based imaging technology has gained great interests in modern photogrammetry and remote sensing. However, due to the limitations of UAS imaging devices, image enhancement (IE) has become a necessary process for improving the visual appearance of UAS images. Although a great amount of effort has been focused on improving image quality from different aspects, the major obstacles are from computational efficiency and complexity, such as manually adjusting the associated algorithmic parameters that account for various image luminance. To overcome these drawbacks, we propose a new adaptive yet highly efficient luminance enhancement method, namely, adaptive trigonometric transformation function (ATTF), for enhancing the visual quality of digital color images captured by a UAS. The ATTF is derived from a tangent-based transformation function whose characteristics adaptively change with respect to the variation of the image luminance. By combining ATTF with a Laplacian operator and a color restoration process, a well-balanced color image is obtained. The effectiveness of the proposed technique is evaluated on various UAS-based images and compared with other IE techniques.