plot coordinate text file for regionprop usage - Matlab - matlab

Question

Based on a previous question (read coordinate text file for regionprop usage - Matlab) I wish to plot the object with an extended boundaries (zeros+10) but it does not work. Any reason why?
Code:
clc;
clear;
filename = fullfile('E:/outline.txt');
fileID = fopen(filename);
C = textscan(fileID,'%d %d');
fclose(fileID);
xMax = double(max(C{1})-10)
yMax = double(max(C{2})+10)
bw=roipoly(zeros(xMax ,yMax ),C{1},C{2});
imshow(bw);
stats = regionprops(bw);
coordinate text file content is as follow:
88 10
87 11
87 12
88 13
88 14
92 21
93 22
93 23
94 24
95 25
100 33
101 34
102 34
103 34
103 33
103 32
103 31
103 30
103 29
103 28
103 27
102 26
102 25
101 24
101 23
100 22
100 21
100 20
99 19
99 18
94 12
93 12
92 12
91 11
90 11

Answer 1

xMax = double(max(C{1})-10)
That should probably be +10. This way you make the image smaller than your polygon.
If you want to extend the image on the left side also, add an offset to your polygon coordinates:
bw = roipoly(zeros(yMax, xMax), C{1}+5, C{2}+5);
Note also that I swapped xMax and yMax from your code, this might be another issue you're seeing. Matrix dimensions are specified as (height, width), as are indices into the matrix. But some functions such as roipoly take coordinates with x first and y second. This is a common pitfall with MATLAB syntax.
I just learned that the above is the same as
bw = roipoly(yMax, xMax, C{1}+5, C{2}+5);