If i want to adjust the brightness for an image by inputting lower and upper limits, what functions should i use?

Same for adjusting contrast. i have to be able to input the lower and upper limits. For GUI.

I've been using imadjust and it doesn't work correctly for my GUI. The LLB is the lower limit, while ULB is the upper limit. please tell me how do i make it work correctly

AFMimage = handles.AFM_Adjust;

LLB = handles.LLB;

ULB = handles.ULB;

adjimage = imadd(AFMimage, [LLB; ULB]);

handles.AFM_Adjust = adjimage;

axes(handles.axes1); imshow(adjimage);

axes(handles.axes4); imhist(adjimage);