To convert a color RGB image to grayscale, use ‘rgb2gray’.

For example:

im = imread(‘image.bmp’); % im is m x n x 3 matrix of RGB values

grayim = rgb2gray(im); % grayim is m x n matrix of intensities

An example to show the image and plot a line from houghlines on top of it, based on the endpoints returned:

%… get lines with houghlines, say there are two:

lines =

1x2 struct array with fields:

point1

point2

theta

rho

% to plot the first one, extract the endpoints from the struct

x1 = lines(1).point1(1);

y1 = lines(1).point1(2);

x2 = lines(1).point2(1);

y2 = lines(1).point2(2);

imshow(im);

hold on;

plot([x1, x2], [y1, y2], ‘r.-‘); % draws red line connecting two points, with dots at the endpoints