Can't convert RGB image to grayscale with button in app designer

Hi, So apparently i want to make an app with matlab app designer that show RGB histogram of an image, and convert it to grayscale and b&w, but i kept getting an error when trying to convert it to grayscale, I don't know what's the problem, So can u guys help me ? The grayscale button called app.Grayscale.

Thank u, Have a great day.

classdef revisi_App < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        figure1       matlab.ui.Figure
        axes1         matlab.ui.control.UIAxes
        axes2         matlab.ui.control.UIAxes
        RedAxes       matlab.ui.control.UIAxes
        LoadGambar    matlab.ui.control.Button
        Reset         matlab.ui.control.Button
        Exit          matlab.ui.control.Button
        RGB           matlab.ui.control.Button
        Grayscale     matlab.ui.control.Button
        BnW           matlab.ui.control.Button
        pushbutton12  matlab.ui.control.Button
        GreenAxes     matlab.ui.control.UIAxes
        BlueAxes      matlab.ui.control.UIAxes
    end

    
    methods (Access = private)
        
        function updateimage(app,imagefile)
            
            % img
            if strcmp(imagefile,'corn.tif')
                im = imread('corn.tif', 2);
            else
                try
                    im = imread(imagefile);
                catch ME
                    % Error message
                    uialert(app.UIFigure, ME.message, 'Image Error');
                    return;
                end            
            end 
            
            % Histogram
            switch size(im,3) > 1
                case 1

                    % Display the truecolor image
                    imagesc(app.axes1,im);
                    
                    % Plotting 2
                    histr = histogram(app.RedAxes, im(:,:,1), 'FaceColor', [1 0 0], 'EdgeColor', 'none');
                    histg = histogram(app.GreenAxes, im(:,:,2), 'FaceColor', [0 1 0], 'EdgeColor', 'none');
                    histb = histogram(app.BlueAxes, im(:,:,3), 'FaceColor', [0 0 1], 'EdgeColor', 'none');
                    
                otherwise
                    % Error when image is not grayscale or truecolor
                    uialert(app.UIFigure, 'Image must be grayscale or truecolor.', 'Image Error');
                    return;
            end
                % Get largest bin count
                maxr = max(histr.BinCounts);
                maxg = max(histg.BinCounts);
                maxb = max(histb.BinCounts);
                maxcount = max([maxr maxg maxb]);
                
                % Set y axes limits based on largest bin count
                app.RedAxes.YLim = [0 maxcount];
                app.RedAxes.YTick = round([0 maxcount/2 maxcount], 2, 'significant');
                app.GreenAxes.YLim = [0 maxcount];
                app.GreenAxes.YTick = round([0 maxcount/2 maxcount], 2, 'significant');
                app.BlueAxes.YLim = [0 maxcount];
                app.BlueAxes.YTick = round([0 maxcount/2 maxcount], 2, 'significant');
         
        end
    end


    % Callbacks that handle component events
    methods (Access = private)

        % Code that executes after component creation
        function revisi_OpeningFcn(app)
%             % This function has no output args, see OutputFcn.
%             % hObject    handle to figure
%             % eventdata  reserved - to be defined in a future version of MATLAB
%             % handles    structure with handles and user data (see GUIDATA)
%             % varargin   command line arguments to revisi (see VARARGIN)
%             
%             % Choose default command line output for revisi
%             app.output = hObject;
%             
%             % Update handles structure
%             guidata(hObject, handles);
            % Configure image axes
            app.axes1.Visible = 'off';
            app.axes1.Colormap = gray(256);
            axis(app.axes1, 'image');

    
        end

        % Button pushed function: BnW
        function BnW_Callback(app, event)
            % hObject    handle to BnW (see GCBO)
            % eventdata  reserved - to be defined in a future version of MATLAB
            % handles    structure with handles and user data (see GUIDATA)
            a=getappdata(0,'a');
            a_bw=im2bw(a,0.4)
            imshow(a_bw, 'Parent', app.axes2);

        end

        % Button pushed function: Exit
        function Exit_Callback(app, event)
            % hObject    handle to Exit (see GCBO)
            % eventdata  reserved - to be defined in a future version of MATLAB
            % handles    structure with handles and user data (see GUIDATA)
            delete(app);
        end

        % Button pushed function: Grayscale
        function Grayscale_Callback(app, event)
            % hObject    handle to Grayscale (see GCBO)
            % eventdata  reserved - to be defined in a future version of MATLAB
            % handles    structure with handles and user data (see GUIDATA)
            a = app.axes1;
            [rows, columns, numberOfColorChannels] = size(a);
            if numberOfColorChannels > 1
                a_gray = rgb2gray(a);
                imshow(a_gray, 'Parent', app.axes2)
            else
                uialert(app.figure1, 'Image must be RGB', 'Image Error');
            end

        end

        % Button pushed function: LoadGambar
        function LoadGambar_Callback(app, event)
               
            % Display uigetfile dialog
            filterspec = {'*.jpg;*.tif;*.png;*.gif','All Image Files'};
            [f, p] = uigetfile(filterspec);
            
            % Make sure user didn't cancel uigetfile dialog
            if (ischar(p))
               fname = [p f];
               updateimage(app, fname);
            end
        end

        % Button pushed function: RGB
        function RGB_Callback(app, event)
            % hObject    handle to RGB (see GCBO)
            % eventdata  reserved - to be defined in a future version of MATLAB
            % handles    structure with handles and user data (see GUIDATA)
            a=getappdata(0,'a');
            imshow(a, 'Parent', app.axes1);
        end

        % Button pushed function: Reset
        function Reset_Callback(app, event)
            % hObject    handle to Reset (see GCBO)
            % eventdata  reserved - to be defined in a future version of MATLAB
            % handles    structure with handles and user data (see GUIDATA)
            clear, clc, close all
        end

        % Button pushed function: pushbutton12
        function pushbutton12_Callback(app, event)
            % hObject    handle to pushbutton12 (see GCBO)
            % eventdata  reserved - to be defined in a future version of MATLAB
            % handles    structure with handles and user data (see GUIDATA)            
            a=getappdata(0,'a');
            red=a;
            red(:,:,2:3)=0;
            imshow(red, 'Parent', app.axes2);
        end

        % Callback function
        function pushbutton13_Callback(app, event)
            % 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)
            a=getappdata(0,'a');
            axes(app.axes2);
            imhist(a);
        end
    end

    % Component initialization
    methods (Access = private)

        % Create UIFigure and components
        function createComponents(app)

            % Create figure1 and hide until all components are created
            app.figure1 = uifigure('Visible', 'off');
            app.figure1.Position = [680 481 1210 617];
            app.figure1.Name = 'revisi';
            app.figure1.Scrollable = 'on';

            % Create axes1
            app.axes1 = uiaxes(app.figure1);
            app.axes1.FontSize = 13;
            app.axes1.TickDir = 'in';
            app.axes1.GridAlpha = 0.15;
            app.axes1.MinorGridAlpha = 0.25;
            app.axes1.XTick = zeros(1,0);
            app.axes1.YTick = zeros(1,0);
            app.axes1.ZTick = zeros(1,0);
            app.axes1.NextPlot = 'replace';
            app.axes1.Position = [27 216 351 301];

            % Create axes2
            app.axes2 = uiaxes(app.figure1);
            app.axes2.FontSize = 13;
            app.axes2.XTick = [];
            app.axes2.YTick = [];
            app.axes2.NextPlot = 'replace';
            app.axes2.Position = [427 209 351 309];

            % Create RedAxes
            app.RedAxes = uiaxes(app.figure1);
            title(app.RedAxes, 'Red')
            xlabel(app.RedAxes, 'Intensitas')
            ylabel(app.RedAxes, 'Pixel')
            app.RedAxes.FontSize = 13;
            app.RedAxes.XTick = [0 128 255];
            app.RedAxes.XTickLabel = {'0'; '128'; '255'};
            app.RedAxes.NextPlot = 'replace';
            app.RedAxes.Position = [777 365 308 160];

            % Create LoadGambar
            app.LoadGambar = uibutton(app.figure1, 'push');
            app.LoadGambar.ButtonPushedFcn = createCallbackFcn(app, @LoadGambar_Callback, true);
            app.LoadGambar.FontName = 'Open Sans';
            app.LoadGambar.FontSize = 19;
            app.LoadGambar.Position = [27 166 351 36];
            app.LoadGambar.Text = 'Load Gambar';

            % Create Reset
            app.Reset = uibutton(app.figure1, 'push');
            app.Reset.ButtonPushedFcn = createCallbackFcn(app, @Reset_Callback, true);
            app.Reset.FontName = 'Open Sans';
            app.Reset.FontSize = 19;
            app.Reset.Position = [27 116 151 36];
            app.Reset.Text = 'Reset';

            % Create Exit
            app.Exit = uibutton(app.figure1, 'push');
            app.Exit.ButtonPushedFcn = createCallbackFcn(app, @Exit_Callback, true);
            app.Exit.FontName = 'Open Sans';
            app.Exit.FontSize = 19;
            app.Exit.Position = [227 116 151 36];
            app.Exit.Text = 'Exit';

            % Create RGB
            app.RGB = uibutton(app.figure1, 'push');
            app.RGB.ButtonPushedFcn = createCallbackFcn(app, @RGB_Callback, true);
            app.RGB.FontName = 'Open Sans';
            app.RGB.FontSize = 19;
            app.RGB.Position = [427 166 351 36];
            app.RGB.Text = 'RGB';

            % Create Grayscale
            app.Grayscale = uibutton(app.figure1, 'push');
            app.Grayscale.ButtonPushedFcn = createCallbackFcn(app, @Grayscale_Callback, true);
            app.Grayscale.FontName = 'Open Sans';
            app.Grayscale.FontSize = 19;
            app.Grayscale.Position = [427 116 151 36];
            app.Grayscale.Text = 'Grayscale';

            % Create BnW
            app.BnW = uibutton(app.figure1, 'push');
            app.BnW.ButtonPushedFcn = createCallbackFcn(app, @BnW_Callback, true);
            app.BnW.FontName = 'Open Sans';
            app.BnW.FontSize = 19;
            app.BnW.Position = [627 116 151 36];
            app.BnW.Text = 'Black & White';

            % Create pushbutton12
            app.pushbutton12 = uibutton(app.figure1, 'push');
            app.pushbutton12.ButtonPushedFcn = createCallbackFcn(app, @pushbutton12_Callback, true);
            app.pushbutton12.FontSize = 11;
            app.pushbutton12.Position = [616 21 91 51];
            app.pushbutton12.Text = 'tes red';

            % Create GreenAxes
            app.GreenAxes = uiaxes(app.figure1);
            title(app.GreenAxes, 'Green')
            xlabel(app.GreenAxes, 'Intensitas')
            ylabel(app.GreenAxes, 'Pixel')
            app.GreenAxes.FontSize = 13;
            app.GreenAxes.XTick = [0 128 255];
            app.GreenAxes.XTickLabel = {'0'; '128'; '255'};
            app.GreenAxes.NextPlot = 'replace';
            app.GreenAxes.Position = [777 197 308 160];

            % Create BlueAxes
            app.BlueAxes = uiaxes(app.figure1);
            title(app.BlueAxes, 'Blue')
            xlabel(app.BlueAxes, 'Intensitas')
            ylabel(app.BlueAxes, 'Pixel')
            app.BlueAxes.FontSize = 13;
            app.BlueAxes.XTick = [0 128 255];
            app.BlueAxes.XTickLabel = {'0'; '128'; '255'};
            app.BlueAxes.NextPlot = 'replace';
            app.BlueAxes.Position = [777 29 308 160];

            % Show the figure after all components are created
            app.figure1.Visible = 'on';
        end
    end

    % App creation and deletion
    methods (Access = public)

        % Construct app
        function app = revisi_App

            % Create UIFigure and components
            createComponents(app)

            % Register the app with App Designer
            registerApp(app, app.figure1)

            % Execute the startup function
            runStartupFcn(app, @revisi_OpeningFcn)

            if nargout == 0
                clear app
            end
        end

        % Code that executes before app deletion
        function delete(app)

            % Delete UIFigure when app is deleted
            delete(app.figure1)
        end
    end
end

Answer 1

[Sampath Rachumallu]

You are directly calling uiaxes handle but not the child that has the image object. To access the image displayed in uiaxes Try to use a = findall(app.axes1, 'type', 'image')

If you have image processing toolbox you can use

imhandles(app.axes1) as well

Instead of using a=app.axes1

[Reyhan Putra]

Thanks, appreciate it!