Question

I want to read an image into MATLAB, draw a rectangle on it, and then save the image.

Also, I’m just learning MATLAB–please be gentle. It seems like it should be simple, but I can’t seem to do it.

im = imread('image.tif'); imshow(im); rectangle('Position', [100, 100, 10, 10]); imwrite(im, 'image2.tif'); 

Even though I can see the rectangle on the image, the saved image does not display the rectangle. How can I save the image and have the rectangle show up?

FWIW, I’ve already tried saveas(), but that gives me a HUGE image. Is there a way to use saveas() and make the saved image the correct size?

Answer 1

There’s actually a bug at The MathWorks site about this issue. Too bad they don’t spell out a real answer (as, IMHO, holding up a ruler to your monitor is not a real solution).

Using the print command, you must manually change the -r parameter until the size of the saved image matches the size of the input image. The -r parameter specifies the DPI of the saved image. Since most screens have different DPIs, there’s no one-size-fits-all solution.

im = imread('image.tif'); f = figure, imshow(im, 'Border', 'tight'); rectangle('Position', [100, 100, 10, 10]); print(f, '-r80', '-dtiff', 'image2.tif'); 

Use the code above, tweak the -r parameter until it looks right, and voilà!