MATLAB: Changing the brightness of an image using slider in Matlab GUI

brightnessbrightness levelbrightness sliderbwgrayscalegrayscale imageguiimageimage brightnessimage processingimportmatlab guiread imagergbslider

I need to create a programme where I can import image (RGB or Grayscale) and with the slider I could change the brightness level of it. It works all well, but I have a problem: grayscale images are detected also as RGB images. Any ideas how to solve it?

Thank you in advance!

My code is below:

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
[filename,pathname] = uigetfile({'*.jpg';'*.bmp'},'File Selector');
fullname=fullfile(pathname,filename);
ImageFile=imread(fullname);
set(handles.text2, 'string', fullname);
handles.im_ax1=imagesc(ImageFile,'Parent',handles.axes1);
handles.im_ax2=imagesc(ImageFile,'Parent',handles.axes2);
axis(handles.axes1,'off')
axis(handles.axes2,'off')
guidata(hObject,handles)
function slider_Callback(hObject, eventdata, handles)
valor=get(hObject, 'value');
new_image=get(handles.im_ax1,'CData')+valor*2.5;
set(handles.im_ax2,'CData',new_image)
set(handles.texto,'string',num2str(valor));
guidata(hObject,handles);
function slider_CreateFcn(hObject, eventdata, handles)
if isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor',[.9 .9 .9]);
end
set(hObject,'Max',100,'Min',-100,'Value',0)
% --- Executes on button press in pushbutton3.
function pushbutton3_Callback(hObject, eventdata, handles)
axes(handles.axes2);
toBeSaved=getframe(gca);
[fileName, filePath] = uiputfile('*.bmp', 'Save As');
fileName = fullfile(filePath,fileName); 
imwrite(toBeSaved.cdata, fileName, 'bmp');
guidata(hObject,handles);
% --- Executes on slider movement.
%function slider_Callback(hObject, eventdata, handles)
%valor=get(hObject, 'value');
%set(handles.texto,'string',num2str(valor));
%guidata(hObject,handles);
% --- Executes during object creation, after setting all properties.

%function slider_CreateFcn(hObject, eventdata, handles)
%if isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
%    set(hObject,'BackgroundColor',[.9 .9 .9]);
%end
function texto_Callback(hObject, eventdata, handles)
edit=get(hObject,'string');
set(handles.slider,'value',str2num(edit));
guidata(hObject,handles);
axes(handles.axes2)
val=0.5*get(handles.axes2, 'value')-0.5;
imbright=(handles.axes2)+val;
imshow(imbright);
axes(handles.axes2);
% --- Executes during object creation, after setting all properties.
function texto_CreateFcn(hObject, eventdata, handles)
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

Best Answer

It probably really is RGB even though it looks like RGB to you. You can cast all images to gray scale like this:

ImageFile=imread(fullname);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(ImageFile);
if numberOfColorChannels > 1
	% It's not really gray scale like we expected - it's color.
	% Use weighted sum of ALL channels to create a gray scale image.
	grayImage = rgb2gray(ImageFile);
else
	grayImage = ImageFile; % It's already gray scale.
end

Related Solutions

MATLAB: How to add brightness slider in matlab gui that would change the second image’s brightness

You should probably be using something like this:

function pushbutton1_Callback(hObject, eventdata, handles)
[filename,pathname] = uigetfile({'*.jpg';'*.bmp'},'File Selector');
fullname=fullfile(pathname,filename);
ImageFile=imread(fullname);
handles.im_ax1=imagesc(ImageFile,'Parent',handles.axes1);
handles.im_ax2=imagesc(ImageFile,'Parent',handles.axes2);
guidata(hObject,handles)
function slider_Callback(hObject, eventdata, handles)
valor=get(hObject, 'value');
new_image=get(handles.im_ax1,'CData')+valor;
set(handles.im_ax2,'CData',new_image)
function slider_CreateFcn(hObject, eventdata, handles)
if isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor',[.9 .9 .9]);
end
set(hObject,'Max',100,'Min',-100,'Value',0)

I would also suggest not using GUIDE, since it makes it more difficult to understand how a GUI works in Matlab and is harder to maintain and edit.

My small guide to avoid GUIDE:

Make a figure (with f=figure;) and look into the doc for figure which properties you want to turn off (you probably want to set Menu and Toolbar to 'none')
Create buttons and axes and everything you need with functions like uicontrol and axes. Save the handles to each element to fields of a struct (like handles.mybutton=uicontrol(___);)
When you've finished loading all data (and saving it to fields of your handles struct), and creating all the buttons, save your handles struct to the guidata of your figure like this guidata(handles.f,handles);. (You can also use getappdata and setappdata)
You can set the Callback property of many objects. If you do, use a function name with an @ in front, or a char array that can be evaluated to valid code. (like @MyFunction or 'disp(''you pushed the button'')')
Callback functions will be called with two arguments: the first is a handle to the callback object, the second is eventdata that may contain special information. To get access to your data, just use handles=guidata(gcbo);. You can replace the gcbo function with the name of the first input to your callback function if you prefer.
More information about callbacks can be found in multiple places in the doc, for example here.

MATLAB: Matlab GUI changing image brightness using slider

Diana - the problem may be with this line of code

imbright=(handles.axes1)+val;

Note that you are adding a value val (calculated based on your slider position to the axes handle and not to the image. I think that what you want to do is save the image (that you have read from file) and then adjust it whenever the slider changes. Your pushbutton1 callback would become somethign like

function pushbutton1_Callback(hObject, ~, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB

% handles    structure with handles and user data (see GUIDATA)

[filename pathname] = uigetfile({'*.jpg';'*.bmp'},'File Selector');
fullname=[pathname, filename];
ImageFile=imread(fullname);
axes(handles.axes1)
imagesc(ImageFile);
axis off;
handles.image = ImageFile;  % <--- new line to save the image to the handles object
guidata(hObject, handles);  % <--- new line to save the updated handles objet

Your slider callback would then look something like

function slider1_Callback(hObject, ~, handles)
% hObject    handle to slider1 (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,'Value') returns position of slider
%        get(hObject,'Min') and get(hObject,'Max') to determine range of slider
if isfield(handles, 'image')
    val=0.5*get(hObject, 'value')-0.5;
    imbright=double(handles.image)+val;               % <--- new line, note the cast to double
    imshow(uint8(imbright), 'Parent', handles.axes1); % <--- new line, note the cast to uint8
end

Note the casting of the image to double before we add the val, and then the cast back to uint8 before we show it on the axes. One or both may not be necessary depending upon the original data type of the image.

Best Answer

Related Solutions

MATLAB: How to add brightness slider in matlab gui that would change the second image’s brightness

MATLAB: Matlab GUI changing image brightness using slider

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