crop image with fixed x/y ratio

I want to crop image using following code. but i want to user only can select the crop area with a predefined x/y ratio.for example if x=2,y=2 ,then user can only use mouse to select an area with (x/y)=1 ratio.

    I = imread('image.jpg');
    [rows columns numberOfColorBands] = size(I);
    I2 = imcrop(I);
    imshow(I), figure, imshow(I2)

Answer 1

[Image Analyst]

You'd have to tie into the mouse move event and draw a box based on the starting point, and some other corner, based on the current mouse location but with the aspect ratio forced to be what you want. Or else just call rbbox() or imrect() and let them draw whatever and fix it up after they finish the box.