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Save pixel color values of all the pixels of an image

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Ouael Chkoundali
Ouael Chkoundali 2019-1-14
评论： Ouael Chkoundali 2019-1-15
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?
  1 个评论
Jan
Jan 2019-1-15
Please post the complete error message, such that we do not have to guess, where the problem occurs.

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采纳的回答

Jan
Jan 2019-1-15
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".

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