Accessing imread image in other functiosn in same file

I am fairly new to matlab. I have read an image using

problemImage = imread("filename")

On my function, I want to access the same file I used in another function. What is the best option, do I have to declare some sort of global variable. If so how?

function selectChannel_Callback(hObject, eventdata, handles)
% Want to access the same image file.  
end

[Rik]

If you want to use data in a callback in a GUI, you can use the guidata function to store and retrieve data.

[Muhammad Umar]

thanks for that, how can i accept this answer ?

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_share_data_between_callback_functions_in_my_GUI.28s.29.3F