Assigning Handles to a variable of an image.

I Need to assign a handles to a variable in my code, however the variable is a variable of an image. I've Taken an image and then reassigned pixel values, to exclude some pixels and highlight others. I now want to take one of those reassigned pixel values and assign a handle to it, so that i can change it as a parameter in a GUI. Can anyone recommend a way of doing this every method I've tried doesn't seem to work. The Relevant code is below. I want to assign a handle to Reassign(C == 3);.

Many Thanks All!

Luke

J = imread('subject04_crisp_v170.png');

%%Pixel Reassign 
Pixel_Reassign = J;
Pixel_Reassign(J==4) = 0;
Pixel_Reassign(J==5) = 0;
Pixel_Reassign(J==6) = 0;
Pixel_Reassign(J==7) = 0;
Pixel_Reassign(J==8) = 0;
Pixel_Reassign(J==9) = 0;
Pixel_Reassign(J==10) = 0;
Pixel_Reassign(J==11) = 0;
C = Pixel_Reassign;

%%Increase Tissue Intensity

Reassign = C;
Reassign(C == 1) = 10;
Reassign(C == 2) = 80;
Reassign(C == 3) = 210;

[Luke Dineen-Woolnough]

This is the function executed by the callback

function pushbutton(hObject, eventdata, edit_text_handle, Reassign_handle)
str_entered = get(edit_text_handle,'string');

if str_entered, 0:255;
    col_val = str_entered;
else 
    col_val = str_entered;
end
set(Reassign_handle, col_val);

The callback is

h.buttonfour = uicontrol('style', 'pushbutton', 'position', [30 350 130 20], 'string', 'Adjust Tissue Value');
set(h.buttonfour, 'callback', {@pushbutton, edit_text_handle, Reassign_handle});

However when i run my gui and try and use this functionality i get the following error

Error using set
Invalid handle

Error in pushbutton (line 9)
    set(Reassign_handle, col_val);

Error while evaluating UIControl Callback

I cant see why there is an error using set in the way i have.

Any help would be appreciated.

Many Thanks all

Luke

Answer 1

[Geoff Hayes]

Luke - you are using Reassign_handle as if it were a handle (to a graphics object) at line

 set(Reassign_handle, col_val);

and the error message is telling you that this isn't a handle. How is this variable initialized? What does it correspond to? Please post more of your code so that we can get an idea of how it is being used elsewhere in your GUI.

Also, when using set it is to update (set) some property of the handle object. In this case, no property is being set so this may not be the function that you want to be using.

[Luke Dineen-Woolnough]

Hi Many Thanks for your response

The Code that initiates this variable is below, apologies it has changed slightly from when i originally posted it at the top of this thread, that is what probably caused the confusion.

I'm attempting to take the variable Reassign_handle(C == 210); and adjust its value using a text box. i have been attempting to get it to work for the variable Reassign_handle = C; before attempting this however.

clear all;

close all;

clc;

h.fig = figure('position', [30 50 1300 600]);

h.buttonone = uicontrol('style', 'pushbutton', 'position', [50 500 100 40], 'string', 'Load Image');

h.buttontwo = uicontrol('style', 'checkbox', 'position', [50 450 100 40], 'string', 'Apply Window');

h.buttonthree = uicontrol('style', 'pushbutton', 'position', [50 400 100 40], 'string', 'Load Histogram');

edit_text_handle = uicontrol('style', 'edit', 'position', [30 300 130 20]);

%%Initialisation

h.axes1 = axes;

subplot(1,2,1);

J = imread('subject04_crisp_v170.png');

%%Pixel Reassign 

Pixel_Reassign = J;

Pixel_Reassign(J==4) = 0;

Pixel_Reassign(J==5) = 0;

Pixel_Reassign(J==6) = 0;

Pixel_Reassign(J==7) = 0;

Pixel_Reassign(J==8) = 0;

Pixel_Reassign(J==9) = 0;

Pixel_Reassign(J==10) = 0;

Pixel_Reassign(J==11) = 0;

C = Pixel_Reassign;

%%Increase Tissue Intensity

Reassign_handle = C;

Reassign_handle(C == 1) = 10;

Reassign_handle(C == 2) = 80;

Reassign_handle(C == 3) = 210;

Many Thanks

[Geoff Hayes]

Luke - but now, none of your push buttons have callbacks. Is this intentional? Why is there a push button that is labelled as "Load Image" but then an image is loaded by default? When should the pixel reassignment and increase to the tissue intensity occur - once the image is loaded, or when the user presses another button? What is the check box for?

Also, your statement I'm attempting to take the variable Reassign_handle(C == 210); and adjust its value using a text box. The variable here is either Reassign_handle (please clarify why this has been named this way) or C. What is the intent of this line of code? How will this change given the text box? i.e. what is being adjusted and how?

Please clarify your workflow. Since you are creating a GUI programatically and not using GUIDE, you may want to change the structure. For example, create a main GUI function with several nested functions that will have access to the local variables declared in the main GUI. One of these nested functions could be that which loads an image when the user presses the Load Image button. See the attached for an example.

[Geoff Hayes]

Luke's answer moved here

Apoligies, hanks for your patience, i should have just pasted mt entire code, please see below

function MRIProjectNoiseGUI

clear all;

close all;

clc;

h.fig = figure('position', [30 50 1300 600]);

h.buttonone = uicontrol('style', 'pushbutton', 'position', [50 500 100 40], 'string', 'Load Image');

h.buttontwo = uicontrol('style', 'checkbox', 'position', [50 450 100 40], 'string', 'Apply Window');

h.buttonthree = uicontrol('style', 'pushbutton', 'position', [50 400 100 40], 'string', 'Load Histogram');

edit_text_handle = uicontrol('style', 'edit', 'position', [30 300 130 20]);

%%Initialisation

h.axes1 = axes;

subplot(1,2,1);

J = imread('subject04_crisp_v170.png');

%%Pixel Reassign 

Pixel_Reassign = J;

Pixel_Reassign(J==4) = 0;

Pixel_Reassign(J==5) = 0;

Pixel_Reassign(J==6) = 0;

Pixel_Reassign(J==7) = 0;

Pixel_Reassign(J==8) = 0;

Pixel_Reassign(J==9) = 0;

Pixel_Reassign(J==10) = 0;

Pixel_Reassign(J==11) = 0;

C = Pixel_Reassign;

%%Increase Tissue Intensity

Reassign_handle = C;

Reassign_handle(C == 1) = 10;

Reassign_handle(C == 2) = 80;

Reassign_handle(C == 3) = 210;

h.buttonfour = uicontrol('style', 'pushbutton', 'position', [30 350 130 20], 'string', 'Adjust Tissue Value');

set(h.buttonfour, 'callback', {@pushbutton, edit_text_handle, Reassign_handle});

%%Noise

mean= 0;

variance = 0.05;

J = im2double(Reassign_handle);

Reassign_handle = J + sqrt(variance)*randn(size(J)) + mean;

imshow(Reassign_handle);

imwrite(Reassign_handle, 'Reassign.png', 'png');

%%Upsampling         

scale = [2 2];              

oldImSize = size(Reassign_Handle);               

newImSize = max(floor(scale.*oldImSize(1:2)),1);  

rowIndex = min(round(((1:newImSize(1))-0.5)./scale(1)+0.5),oldImSize(1));

colIndex = min(round(((1:newImSize(2))-0.5)./scale(2)+0.5),oldImSize(2));

opImage = Reassign_Handles(rowIndex,colIndex,:);

im16 = double(opImage)*65535/255;

B=im16;

Im1 = fftshift(fft2(B));% complex matrix;

%%Rectangular window

dims=size(opImage);

filtprop=0.1; %relative size of rectangular window in Fourier domain in relation to size of original data

lpdims=round(dims*filtprop);

zeroout=dims-lpdims;

lpdims=lpdims+mod(zeroout,2);

zeroout=zeroout-mod(zeroout,2);

rectwin = 
padarray(ones(lpdims(1),1),double(zeroout(1)/2))*padarray(ones(lpdims(2),1),double(zeroout(2)/2))';

w_new = Im1.*rectwin;

%%IFFT

Im2 = ifft2(fftshift(w_new));

imwrite(uint8(abs(Im2)), 'Im2.png', 'png');

title ('Image after IFFT');

%%CallBack

set(h.buttonone, 'callback', {@addaxes1, h});

set(h.buttontwo, 'callback', {@applywindow, h});

set(h.buttonthree, 'callback', {@Hg, h});

[Geoff Hayes]

Luke - I would rather that you had answered my questions instead of posting more code. It is unclear (from the above) whether all the code should execute immediately upon launching the GUI or if some of the code should fire depending upon which button the user has pressed.

I've attached a simplified version of your GUI. It has two buttons: one to load the image and one to load the histogram for that image. The callbacks are nested so that they have access to the local variables declared within the main GUI function. Note in particular how the loadImage callback allows the user to choose an image, myImg, which gets displayed in the left axes. When the user presses the other button, the loadHistogram callback uses that same myImg to determine the histogram for that image. Which I'm hoping is what you are trying to accomplish - access the same object (your "handle") between different callbacks/functions.

Use the attached as a guide to construct your own GUI. Also, please comment your code to make it clearer to the reader what is happening and what is supposed to happen. Assign your variables names that make sense and that are clear from the context what they should represent.

[Luke Dineen-Woolnough]

Hi Geoff, Thank you so much for your help, the layout of this GUI has helped alot to see what im trying to do. To better explain it. I am trying to take the value of a slider, ranged from 0 to 255 and use it to update the value of the variables Reassign(C == 1)Reassign(C ==2)Reassign(C == 3). I have no problem assigning a handle to Reassign but im struggling to do it to these individual variables.

function MRIGui

    % clean up the workspace
    clear all;
    close all;
    clc;

    % create the GUI
    handles.fig = figure('position', [30 50 1300 600]);
    handles.loadImageBtn = uicontrol('style', 'pushbutton', 'position', [50 500 100 40], 'string', 'Load Image');
    handles.loadHistBtn  = uicontrol('style', 'pushbutton', 'position', [50 400 100 40], 'string', 'Load Histogram');

    % assign the callbacks for each button
    set(handles.loadImageBtn,   'callback', @loadImage);
    set(handles.loadHistBtn, 'callback', @loadHistogram);

    % create the axes
    handles.subplotImg  = subplot(1,2,1);
    handles.subplotHist = subplot(1,2,2);

    % initialize variables to be accessible by callbacks
    myImg = [];
    Reassign = [];

    % load image callback
    function loadImage(hObject,eventdata)

        [filename,filepath] = uigetfile({'*.jpg;*.png'},'Select image...');
        filenameAndPath     = fullfile(filepath,filename);
        myImg = imread(filenameAndPath);
        myImg = myImg(:,:,1);  % ensure 2D only

        %%Pixel Reassign 
        Pixel_Reassign = myImg;
        Pixel_Reassign(myImg==4) = 0;
        Pixel_Reassign(myImg==5) = 0;
        Pixel_Reassign(myImg==6) = 0;
        Pixel_Reassign(myImg==7) = 0;
        Pixel_Reassign(myImg==8) = 0;
        Pixel_Reassign(myImg==9) = 0;
        Pixel_Reassign(myImg==10) = 0;
        Pixel_Reassign(myImg==11) = 0;
        C = Pixel_Reassign;

        %%Increase Tissue Intensity

        Reassign = C;
        Reassign(C == 1) = 160;
        Reassign(C == 2) = 80;
        Reassign(C == 3) = 210;
        Reassign(C == 0) = 0;

        image(Reassign,'Parent',handles.subplotImg);
        colormap(gray(256));
    end

    % load histogram callback
    function loadHistogram(hObject,eventdata)

        if ~isempty(Reassign)
            hist(handles.subplotHist,Reassign(:),1:256);
        end

    end

end

[Geoff Hayes]

Luke - Reassign is a variable, so I don't understand what you mean by ..have no problem assigning a handle to Reassign. As for the slider (which wasn't included in your original code?), is its value used in the C==X (i.e. is the value for X) or is it is used in the assignment (i.e. Reassign(C==1) = X;).

Please clarify what a handle means to you within the context of your code.

[Luke Dineen-Woolnough]

So where Reassign(C == 1) = X, i want to use the slider to update X between 0 and 255. I didn't mean assigning a handle to reassign, apoligies, i meant assigning Reassign to a callback.

[Geoff Hayes]

Why did you post the code from the GrayScaleImageHistogramGui.m example in your above comment (with the only difference being the renaming of the function)? It was provided as an example of what you can do. It is no longer clear to me what it is that you are expecting...