Image Processing for Spray Pattern Analysis

Original scanned spray pattern This pattern is made by spraying an alcohol solution on alcohol sensitive paper using a typical consumer spray pump.

Target is a program designed assign a rating to a picture of a spray pattern, The rating varies from 0 to 100, the higher the score the better the pattern. (A good pattern in one that is most circular). The first step is to threshold the image and find the centroid of the dark pixels

The rating is determined by the ratio of two areas, the numerator is the area of the primary circle. The denominator is the sum of the primary circle area and the secondary area.

These two areas are determined by placing a target over the pattern image. The target is divided into sectors based on the polar coordinate system. Each sector of the pattern is investigated to determine the number of pixels in the sector that are covered by the spray pattern or left uncovered.

The primary circle is the largest circle with center at the target center that has all sectors covered at least the primary coverage percent, usually 75 percent. The secondary area is the sum of the areas of all sectors outside of the primary circle that are covered at least the secondary coverage percent, usually 50 percent.

This program loads a raw image and then processes the image in steps to obtain the rating. Parameters such as Threshold, DPI, Target size and Center, and coverage percents can all be changed to allow for modification of the rating process.

Thresholded image

This image is a pattern image that has had a target placed over the image. Clearly there are sectors that are completely covered and sectors that are only partially covered. And then there are sectors that have no dark pixels at all.

This is the final output window. The program has determined which sectors are 50% covered and which are 75% covered and calculated the rating. This program includes an installer, a help file, and a tutorial. It is used in the client's facilities in the U.S. Spain, and Germany. It was featured in Spray Technology Magazine.