Usage

• Press the "Load" button (or Ctrl-O) to open a movie file in Motion-JPG (MJPG) format. A suitable sample file (sample.avi) comes with the distribution.

Next, you have to set a couple of parameters with the sliders below the image.

• First, adjust the threshold slider so that you get the best possible shape with sharp edges of the droplet. For the sample movie, a value of 110 is good. This parameter is usually not critical.
• Second, adjust the baseline (the horizon): Move the "base left" slider and see how the red edge of the droplet at the left side goes up an down. To the right of the image there is a plot window in which you see the edge points of the droplet in blue (corresponding to the red line in the image). The thin red line in the plot window is the best parabolic fit through the points. The goal is to adjust the slider so that the point where the droplet touches the surface is the lowest blue point in the plot window. The correct value for the sample is about 263.
• Repeat the same for the "Base right" slider and the right plot window, a good value for the sample is 261.
• Adjust the "NumofPoints" slider to change the number of points (as shown in the plot windows) to get a good fit, meaning that the thin red lines in the plot windows do not deviate from the blue edge points. In general, the more points, the more precise the fit, but if the line deviates from the points, you will get the wrong number. In reality this is usually not critical and you don't need too many points. For the sample, 80 points is just fine.
• Finally, by moving the "Frame number" slider, check that the values you have selected are good for all frames in the movie. The left and right contact angles and tangents are shown in the image.

• Press the "Analyze movie" button and the program will go through all the frames and write the corresponding left and right contact angle to a comma-separated text file with the extension ".txt", for the sample "sample.avi" this will be "sample.txt". This file can the be used directly (e.g. with Matlab) or imported into some spreadsheet.

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