MATLAB: InsertShape function doesn’t read color triplet

Question

The function is able to read colors as strings ('red', 'green'…etc…) but cannot read modified color vectors like [1 0 0] or [0.6 1 0.2]. If I use this as an input the shape just come out black.

My color triplet is type double.

Here is the line:

img = insertShape(img, 'Line', position(i,:), 'Color', ColMap(c,:), 'LineWidth', w);

position and line width are perfect. ColMap ia a Mx3 matrix double.

What I dont understand is that using the function 'plot' to simply plot a line over an image everything works perfectly including the color. Meaning, the following line works:

line = plot([x1 x2], [y1 y2], 'Color', ColMap(c,:), 'LineWidth', w);

Any idea?

thank you

Answer 1

Unlike other functions that require colors in the range 0-1, insertShape expects values in the range 0-255: Try this:

% Try it with a gray scale image.
img = imread('moon.tif');
position = [50, 20, 200, 500];
i = 1;
w = 13;
c = 220;
ColMap = jet(256); % In the range 0-1
customColor = round(255 * ColMap(c, :))
img = insertShape(img, 'Line', position(i,:), 'Color', customColor, 'LineWidth', w);
% img is now converted into an RGB image.  No longer a gray scale image.
subplot(2, 1, 1);
imshow(img);
axis('on', 'image');
% Try it with a color image.
img = imread('peppers.png');
img = insertShape(img, 'Line', position(i,:), 'Color', customColor, 'LineWidth', w);
subplot(2, 1, 2);
imshow(img);
axis('on', 'image');