Save pixel color values of all the pixels of an image

Hello,

I am trying to save the pixel color values of an image in a matrix after uploading it on GUI.

First I choose the image with the browser button. I wrote a function, that firtst converts the image in gray and then saves using a for loop all pixel values in the Matrix pixelValues.

I receive the error "Index exceeds matrix dimensions."

Here is my code for the browser button

% --- Executes on button press in browser.
function browser_Callback(hObject, eventdata, handles)
% hObject    handle to browser (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
[a b] = uigetfile({'*.jpg';'*.png';'*.bmp'},'File Selector');
image = imread([b a]);
axes(handles.axes)
imshow(image)
axis on
yLimits = get(gca,'YLim');  %# Get the y axis limits
yTicks = yLimits(2)-get(gca,'YTick');  %# Get the y axis tick values and
                                       %#   subtract them from the upper limit
set(gca,'YTickLabel',num2str(yTicks.'));  %'# Convert the tick values to strings
                                           %#   and update the y axis labels
A = savePixelValues(image);

And here is the function :

function [pixelValues] = savePixelValues(image)

[x,y,z] = size(image);
I = rgb2gray(image);
v = zeros(1,3);
A = zeros(y,x);
for i=1:y
     for j=1:x
       v = squeeze(I(i,j,:));
        pixelValues(i,j) = v(1);
    end
end
end

Can someone help me please?

[Jan]

Please post the complete error message, such that we do not have to guess, where the problem occurs.

Answer 1

[Jan]

Some hints:

% Use meaningful names for variables. "[a b]" is confusing:
[fileName, filePath] = uigetfile({'*.jpg';'*.png';'*.bmp'},'File Selector');
% FULLFILE is smarter than [filePath fileName]:
img = imread(fullfile(filePath, fileName));
% "image" is an important command, do not shadow it by a variable.
% It is safer to provide the parent than to rely on the 
% current axes by: axes(handles.axes)
imshow(img, 'Parent', handles.axes);
axis(handles.axes, 'on');
yLimits = get(handles.axes,'YLim');   % If you have the handle already, ...
% requesting  GCA wastes time only.
% Puh, Matlab is not twitter. No hash characters before comments.
% %# Get the y ax
yTicks = yLimits(2)-get(handles.acers,'YTick');
set(handles.axes,'YTickLabel',num2str(yTicks.'));
A = savePixelValues(img);

Your code:

[x,y,z] = size(image);
I = rgb2gray(image);
v = zeros(1,3);
A = zeros(y,x);
for i=1:y
     for j=1:x
       v = squeeze(I(i,j,:));
        pixelValues(i,j) = v(1);
    end
end

could be simplified to the single line:

pixelValues = I(:,:,1);

Pre-allocating v is a waste of time, because you re-create the array in each iteration. A is not used anywhere. But most of all, I is a 2D matrix already after rgb2gray. So you can can be written as:

function pixelValues = savePixelValues(rgb)
pixelValues = rgb2gray(rgb);
end

I assume you mean the gray value as "pixelValue".

[Ouael Chkoundali]

Thanks a lot Jan!