What does the Lower limit & Upper limit represents? & Why must i give the lower & upper limit? For Adjusting contrast & Brightness.

Contrast:

function LLC_Callback(hObject, eventdata, handles)
% hObject    handle to LLC (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of LLC as text
%        str2double(get(hObject,'String')) returns contents of LLC as a double

LLC  = str2num(get(handles.LLC,'String'));

handles.LLC = LLC;

% Update handles structure
guidata(hObject, handles);

% --- Executes during object creation, after setting all properties.
function LLC_CreateFcn(hObject, eventdata, handles)
% hObject    handle to LLC (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

function ULC_Callback(hObject, eventdata, handles)
% hObject    handle to ULB (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of ULB as text
%        str2double(get(hObject,'String')) returns contents of ULB as a double

ULC  = str2num(get(handles.ULC,'String'));

handles.ULC = ULC;

% Update handles structure
guidata(hObject, handles);

% --- Executes during object creation, after setting all properties.
function ULC_CreateFcn(hObject, eventdata, handles)
% hObject    handle to ULB (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

% --- Executes on button press in pushbutton13.
function adjust_contrast_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton13 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

AFMimage = handles.AFM_Adjust;
LLC = handles.LLC;
ULC = handles.ULC;

adjimage = imadjust(AFMimage,[LLC ULC],[]);
handles.AFM_Adjust = adjimage;

axes(handles.axes1); imshow(adjimage);
axes(handles.axes4); imhist(adjimage);

% Update handles structure
guidata(hObject, handles);

Brightness:

function LLB_Callback(hObject, eventdata, handles)
% hObject    handle to LLC (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of LLC as text
%        str2double(get(hObject,'String')) returns contents of LLC as a double

LLB = str2num(get(handles.LLC,'String'));

handles.LLB = LLB;

% Update handles structure
guidata(hObject, handles);

% --- Executes during object creation, after setting all properties.
function LLB_CreateFcn(hObject, eventdata, handles)
% hObject    handle to LLC (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

function ULB_Callback(hObject, eventdata, handles)
% hObject    handle to ULB (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of ULB as text
%        str2double(get(hObject,'String')) returns contents of ULB as a double

ULB = str2num(get(handles.ULB,'String'));

handles.ULB = ULB;

% Update handles structure
guidata(hObject, handles);

% --- Executes during object creation, after setting all properties.
function ULB_CreateFcn(hObject, eventdata, handles)
% hObject    handle to ULB (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

% --- Executes on button press in adjust_brightness.
function adjust_brightness_Callback(hObject, eventdata, handles)
% hObject    handle to adjust_brightness (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

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);

% Update handles structure
guidata(hObject, handles);

Answer 1

[Image Analyst]

Those are the values from your input image that will get mapped to 0 and 1 (black and white).