why is impoly so slow?

Can someone explain to me why it takes approximately 2.5 seconds for impoly to create a simple object using my 2.8GHz quad core Xeon with 32GB?

See code below:

clear all;
clear classes;
close all;
clc;

I=imread('pout.tif');
figure,imshow(I);
a_iXY=[47,184;39,158;37,58;145,52;163,144;];

hGCA=gca;
tic
hImpoly=impoly(hGCA,a_iXY);
toc

Answer 1

[Dan]

I did some digging and found that impoly eventually calls /Applications/MATLAB_R2015a.app/toolbox/images/imuitools/private/polygonSymbol.m which (amazingly) spend almost a full second reading in "point.png" using imread! I think these are just the vertices of the polygon. It seems like this is very wasteful....