Placing multiple rectangles using imrect in GUI

Hi everyone!

I am new to gui creation in Matlab and have just worked through the simple Gui tutorial.

What I want to do is the following:

load an image -> drag multiple (e.g. 3) rectangles over the roi using imrect with a specific size (e.g. 32x100 px) and then get the coordinates to process the image only in the specified region by an edge detecting algorithm I programmed.

I am loading and displaying the image using a pushbutton

handles.img_in=imread(load_im());
guidata(hObject,handles)

imshow(handles.img_in);

and I know I can draw a rectangle and get the position via another pushbutton

h=imrect;
rect=uint16(getPosition(h));

can someone help me with the next step that is fixing the size of the rectangle and how to store the data for every instance I click the button and place a rectangle properly?

Every help is appreciated!

Best Wishes, Chris

Answer 1

[Image Analyst]

I don't think you can constrain imrect(), rbbox(), or getrect() to work with fixed size rectangles and not allow the user to change the size of the rectangle. The workaround is to have two scroll bars, one for vertical movement and one for horizontal movement. The slider callbacks will calculate the new position of the box sides and draw it using plot(). Then the user clicks an OK button. In fact I do this for some of my apps.

The alternative is to use dragrect(). I haven't used this before. Here is the description from the help:

Examples

Drag a rectangle that is 50 pixels wide and 100 pixels in height.
waitforbuttonpress
point1 = get(gcf,'CurrentPoint') % button down detected
rect = [point1(1,1) point1(1,2) 50 100]
[r2] = dragrect(rect)

Tips

dragrect returns immediately if a mousebutton is not currently pressed. Use dragrect ina ButtonDownFcn, or from the command line in conjunctionwith waitforbuttonpress, to ensure that the mousebutton is down when dragrect is called. dragrect returnswhen you release the mouse button.

If the drag ends over a figure window, the positions of therectangles are returned in that figure's coordinate system. If thedrag ends over a part of the screen not contained within a figurewindow, the rectangles are returned in the coordinate system of thefigure over which the drag began.

Note:  You cannot use normalized figure units with dragrect.

[Christoph]

Thank you, this is already a great idea and helps me a lot!

Do you know an easy and realiable solution to draw and store multiple of those rectangles? I was thinking about counting how often the button draw rectangle is pushed and then use this as a counting variable, but probably this is not a good way?

kind regards, Chris

[Image Analyst]

You could store the different rectangle parameters in a global variable. When you click it again, just append it

global allRects;
% Now get a new rect, thisRect, and append it to the global one.
allRects = [allRects; thisRect];

[Christoph]

Thank you very much! :)

[Christoph]

do you know if the dragrect uses some coordinates different than the image?

If I drag a rectangle and then give the coordinates to

rectangle('Position',r2);

it always plots somewhere else than the drawing area!

[Image Analyst]

I haven't used it yet. But a common problem is confusing x,y with row,column. The order is reversed: x,y = column,row, not row,column. Could that be the problem?

[Christoph]

actually it was my mistake because I segmented the image in a wrong way previously!

Thank you for helping it works quite okay now! :)