# Calculate the cone angle of a spray image

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sanjeet on 13 May 2015
Edited: Image Analyst on 16 Jul 2021 at 0:07
Please find the image bellow - the angle is between the boundary lines in red shown, while the reference point is the center point in the line shown as reference. The reference point is at fixed distance known value. The dark fish shaped is the spray shape after impingement- for which we need to measure the angle. Scattered dots are particle in liquid form-
To tackle I thought to get following steps: read the image Subtracting image with background image to get clear spray visualization convert grey-scale to binary setting threshold for separating the dark and light area- for boundary Drawing the boundary lines as spray after collision and calculating the angle between lines
sanjeet on 13 May 2015
My actual image to be processed is
My matlab code:
% Calculate the cone angle of a spray image
clear, clc, close all
[a1 a2 a3]=size(Image);
x0=215; %if picture higher than increase number 215
y0=255; %if picture to the left than increase number 255
r=170; %170
figure(1); imshow(Image2)
hold on
BW = im2bw(Image2);
figure(2); imshow(BW)
BW1 = edge(BW,'sobel');
figure(3); imshow(BW1);
size(BW1)
I am getting the image as
My next step is to get scan pixel to get a line to represent the spray edge as shown in image earlier. They should start from intersection at reference point. I tried using bwtraceboundary and find but unable to create boundary along the edge inner. Please guide me to get the line along the desired spray edge.

Image Analyst on 14 May 2015
Edited: Image Analyst on 16 Jul 2021 at 0:07
Alright sanjeet, I spent way more time than I should have to make this fancy for you (about half an hour) but attached below the image is the code.
It determined that the angle is 23.1 degrees. If you want the lines overlaid on the image, I'm sure you can figure out that simple part. As I mentioned in the comments you might want to figure out an algorithm to examine the widths plot and figure out where to fit your line over. The min is fairly straight forward, but the widest part is somewhat of a judgement call.
sanjeet on 14 May 2015
Thanks a lot
I got 24 degree as cone angle on increasing the threshold value to 65 from 40... which matches with that measure by protector using paint shop

Dhruv Gandhi on 29 Apr 2019
Hallo image analyst,
i want to calculate the area of the coloured image , see the attachment.
i try to convert all the blue lines into white and other then Blue in to Black. after That want to calculateArea of this Black region in the image. i Dont know How to do that. can ypu please Help.