how to get image position in a figure, for annotation purpose

I am displaying an image with imshow in a GUI window. What I want to do is to add arrow annotations on the image at the places of mouse clicks.

The problem that I am having, is that annotation function uses normalized figure units, and I will need the position information of the image displayed in the figure to convert between the coordinates for a point in the image to the coordinates of the point in the figure.

I tried ds2nfu, but it does not work properly, because it is only taking the position info for the axes that the image is displayed in, whereas imshow displays the image with the original aspect ratio, leading to inconsistency between image coordinates and axes coordinates.

Any suggestion is appreciated

Answer 1

[Image Analyst]

Did you try ginput()? It will return the pixel position in the image.

[Patrick Kalita]

Moving Jun's reply from a separate answer to a comment in this thread: "I did use ginput, which returns to me the current cursor position in the image. But what I want to know is how I can translate this ginput position to the coordinates of the figure that the image is in."

[binbin cui]

By the way, how to make sure the position selected by hand is exactly accurate and precise.

Answer 2

[Sean de Wolski]

Set the figure 'units' to 'pixels' and then ginput will correspond directly.