Drop Shape Analysis
Written by Aurélien Stadler and Daniel Sage
Contact angle is a simple and yet powerful tool for characterizing three-phase junctions.
The technique of the sessile drop is today the most widely used method to measure this parameter.
The commercial softwares available today are still very limited.
They are often dependant of one measurement setup, and may fail under non-standard conditions.
We propose, here, two new methods to high-accuracy measure contact angles:
These methods have been implemented as a Java plug-in for the ImageJ software and we make it freely available. See the "free software" section to download.
- DropSnake is based on B-spline snakes (active contours) to shape the drop.
- LBADSA is based on the fitting of the Young-Laplace equation to the image data
 A.F. Stalder, T. Melchior, M. Müller, D. Sage, T. Blu, M. Unser, "Low-Bond Axisymmetric Drop Shape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops," Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010.
 A.F. Stalder, G. Kulik, D. Sage, L. Barbieri, P. Hoffmann, "A Snake-Based Approach to Accurate Determination of Both Contact Points and Contact Angles," Colloids And Surfaces A: Physicochemical And Engineering Aspects, 2006.
- Interface detection: Considering that the interface position is a crucial parameter when measuring contact angle,
the drop reflection has been integrated into the drop model, so that to detect the interface position.
- Interpolated gradient-based energy: In order to provide high precision contact angle on a wide range of
images, a drop detection method based on image gradient energy and cubic spline interpolation has been used.
Based on this framework, two complementary drop models have been designed.
- B-Spline Snake The B-snake approach provides a novel methodology
suitable to drops that do not follow a global model. Its new model is
based on B-spline snake which in reason of their elasticity unify the
aspects of locality of the contact angle to the guidance provided by the
global drop contour. With this approach, the whole drop shape is used to provide
global information, nevertheless, the contact angle measurement remains local
and similar to a polynomial fit.
- Low Bond Axisymmetric Drop Shape Analysis This model is derived from a first order perturbation solution
of the Laplace equation for axisymmetric drops. Using this global model of a drop,
contact angles are obtained considering the whole drop profile. While offering a fair domain of
application, this approximation is computationally much more efficient than a solution obtained
from numerical integration (ADSA approach).
Free software for high precision contact angle measurement
The software is based on a plugin for ImageJ, a general purpose free image-processing package.
ImageJ has a public domain licence; it runs on several plateforms: Unix, Linux, Windows and Mac OS X.
Some users have encountered incompatibility with ImageJ versions higher than 1.47.
In case of troubles, we recommend to use the ImageJ version 1.46 including Java.
This version ij147-jdk6-64bit-setup.exe or ij147-jdk6-setup.exe is available at:
Get a copy of ImageJ. and download the plugin drop_analysis.zip.
Extract drop_analysis.zip in the "plugins" folder of ImageJ. All the files should extract in a new folder "drop_analysis".
The whole process should not take more than a couple of minutes.
2. How of use
Open a drop image. Ensure that the image is grayscale.
In the "plugin" menu, go under "drop_analysis" and choose one of the two methods: "LB_ADSA" or "DropSnake".
4. Conditions of use
You are free to use this software for research purposes, but you should not redistribute it without our consent.
In addition, we expect you to include adequate citation whenever you present or publish results that are based on it.
|DropSnake plugin||LBADSA plugin|
Thanks to Laura Barbieri and to Marco Brugnara for the images.
- the ImageJ's plugin
- the manual
- an image sample
Some of the unzip tools produce a drop_analysis folder inside of a drop_analysis folder.
This hierarchical structure is not compatible for the image plugins.
The correct structure is: ImageJ » plugins » drop_analysis » drop_analysis.jar