how to fix Cell contents assignment to a non-cell array object.?

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noam Y 2017-10-20

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评论： noam Y 2017-10-21

hallo I'm trying to create a 2D by N dimentions pictures features array to save code running time so i created the next code:

 SurfFeatures = {};
folderlisting = dir('C:\Documents\');
for item=3:1:numel(folderlisting)
    name = folderlisting(item).name;
    Fname = strcat('C:\Documents\',name);
    comperimg = imread(Fname);
    comperimg = comperimg(:,:,1:3);
I = rgb2gray(comperimg);
points = detectSURFFeatures(I);
[features,valid_points] = extractFeatures(I,points);
    SurfFeatures{item-2}  = features;
end
save('SurfFeatures.mat','SurfFeatures');

I keep getting the next error right after the code enters the part of the feature assignment "Cell contents assignment to a non-cell array object."

happy for help :) .

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OCDER 2017-10-20

编辑：OCDER 2017-10-20

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I don't see anything wrong, but perhaps the error is in extractFeatures or detectSURFFeatures. Here are some tips to improve the code though.

FolderList = dir(fullfile('C:\Documents\', '*.jpg')); %Use file extensions since dir will also return "." and ".." folders, + other files
SurfFeatures = cell(1, numel(FolderList) - 2);        %Preallocate for speed
for item = 3:numel(FolderList)
    %name = FolderList(item).name; %Uppercase notation. Also, this isn't needed.
    %Fname = strcat('C:\Documents\',name); %fullfile is better
    %comperimg = imread(Fname); 
    %comperimg = comperimg(:,:,1:3); %squeeze will remove singleton dimension
    Fname = fullfile('C:\Documents\',FolderList(item).name);
    I = squeeze(imread(Fname)); 
    I = rgb2gray(I);
    Points = detectSURFFeatures(I);
    [Features, ValidPoints] = extractFeatures(I, Points);  
    SurfFeatures{item-2}  = Features;
end
save('SurfFeatures.mat','SurfFeatures');

Be consistent when using camelcase notation to help you determine what is a function vs variable. I noticed a partial implementation, which can get confusing later (ex: valid_points vs ValidPoints). Using uppercase is generally good for variables, to prevent overriding a matlab function by accident. You're function naming scheme is fine

noam Y 2017-10-21

thanks a lot that fixed it. but why because I didn't assign it first to be a cell array?

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