A new method for measuring the contact angles from digital images of liquid drops

•A novel image processing method has been developed to measure the contact angle of both symmetric and asymmetric drops from side views of drops.•The proposed algorithm does not require any liquid property value, while also does not require drop edge fitting with analytical curves; hence it is suitable for automated computer implementations.•The error for the method is in the order of 1° over the contact angle of the images of other articles.•The advantages of this method are; the ability to measure accurately contact angles with a completely automatic process for detecting the contact points. The drop hitting a solid surface may be symmetric or asymmetric, which depends on the surface texture and external force orientations. The accurate measurement of the contact angle is of fundamental importance for the purpose of scientific research, while having a substantial role in a wide range of practical applications. This paper presents a new image processing based method, as a computational scheme to measure the inclination angle of apparent edge curves in digital images. The main concept of the scheme is the emulation of a moving goniometer mask coupled with a Gaussian weighted function, which does not require edge fitting with analytic curves for the angle calculation. The algorithm produces as follow: allocating the exact position of the contact points by Harris corner detector function, selecting a series of points on the drop boundary near the contact points, setting goniometric mask on each given point and calculating the angles, applying the Gaussian weighted average function on the calculated angles and measure the objective contact angle. The scheme is tested on several images from recent studies in the available literature. The comparison between analytical and calculated angles shows less than 1° difference.