The exact spray edge is sometimes hard to define because sprays often lose definition downstream of the nozzle. As seen in Figure 1, the spray shape begins to curve in due to the surrounding air and no longer has a distinct cone shape. It is therefore ideal to conduct spray angle measurements closer upstream.
The spray angle for this effort was calculated from the high speed video recordings. 10 frames over the course of 100 frames were first converted from RGB to black and white based on an intensity threshold of 25%. The black and white conversion was done to simplify matrix calculations and the exact threshold was selected by eye (by trial and error) to maximize the contrast between the spray and the background. These 10 images were averaged into one representative image.