Putting visual marker in an image

I'd like to be able to simply mark a point on an image using a crosshair or something similar. It's not a plot I'm using, I want to be able to overlay the marker on the actual image at a particular point.

[Walter Roberson]

My interpretation is that the marker needs to be written into the image.

[Image Analyst]

Please clarify if you want the cross mark in the overlay (above the image) or if you want it actually written into the image pixels themselves.

Answer 1

[Image Analyst]

Try this:

grayImage = imread('moon.tif');
imshow(grayImage);
uiwait(msgbox('Locate the point'));
[x,y] = ginput(1);
hold on; % Prevent image from being blown away.
plot(x,y,'r+', 'MarkerSize', 50);

[Youssef Khmou]

efficient !

[khalid jackson]

Is there any way to make sure the point doesn't get overlayed by filters that are added to the image?

[Image Analyst]

What do you mean by "filters that are added to the image"?

[khalid jackson]

Say, for instance, after placing the marker on 'grayimage' I did binaryimage = im2bw(grayimage);. If i do imshow(binaryimage) the image appears to be written over the marker; is there a way to always keep the marker above the image?

[Image Analyst]

No. If you show another image, it blows away whatever was in the axes. So you have to put "hold on" and then call plot() to place your points into the overlay above the image again.

You might look into imoverlay() - not sure if that will keep the overlay points since I haven't tried it.

[khalid jackson]

Okay, thank you very much.

Answer 2

[Youssef Khmou]

hi Con

You can use 'gtext', and put the dot in a position you want , example :

 X=imread('circuit.tif');
 imshow(X), gtext('*')

You can also make many text strings using the same function :

X=imread('circuit.tif');
figure,imshow(X), gtext({'My point1';'My mpoint2';'My point3'})