A Novel Shadow Removal Method Based upon Color Transfer and Color Tuning in UAV Imaging

Abstract

Through the increasing use of unmanned aerial vehicles as remote sensing tools, shadows become evident in aerial imaging; this fact, alongside the higher spatial resolution obtained by high-resolution mounted cameras, presents a challenging issue when performing different image processing tasks related to urban areas monitoring. Accordingly, the state-of-the-art reported works can correct the shadow regions, but the heterogeneity between the corrected shadow and non-shadow areas is still evident and especially noticeable in concrete and asphalt regions. The present work introduces a local color transfer methodology to shadow removal which is based on the CIE L*a*b (Lightness, a and b) color space that considers chromatic differences in urban regions, and it is followed by a color tuning using the HSV color space. The quantitative comparison was executed by using the shadow standard deviation index (SSDI), where the proposed work provided low values that improve up to 19 units regarding other tested methods. The qualitative comparison was visually realized and proved that the proposed method enhances the color correspondence without losing texture information. Quantitative and qualitative results validate the results of color correction and texture preservation accuracy of the proposed method against other published methodologies.

Shadow Removal from UAV Images Based on Color and Texture Equalization Compensation of Local Homogeneous Regions

“…Overall, the global strategy can produce better shadow compensation results, but still has some shortcomings in dealing with the shadows of UAV images with complex surface features and a wide variety of objects. For example, a local color transfer algorithm is proposed by Gilberto et al [41] which can accurately correct the color without losing texture information, but the restored image has obvious shadow boundaries. Therefore, how to accurately compensate for shadows remains to be studied in more depth.…”