How to access a variable of one callback function in another function in gui?

I have browsed an image using a pushbutton and stored it in a variable(let it be 'sm'). Now I want this image('sm') in callback function of another pushbutton so that I convert that image here.

[Stephen23]

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

If you are not using GUIDE I would recommend using nested functions: simple and intuitive. Otherwise use handles and guidata.