How can a code run on a single image perfectly, but the same code on an entire database crashes? Where am I going wrong?

Question

Andreea Stancu 2019-6-21

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评论： Jan 2019-6-24

When I run the code on an image database it gives this error and I don't know why, because when I run the test on a single image it works perfectly.

The code looks like this:

for i=1:80
imag_open(i).normal=imopen(M_filt1(i).normal, ones(20));
imag_close(i).normal=imclose(imag_open(i).normal, ones(20));
[imag_etich(i).normal, maxL(i).normal]=bwlabel(imag_close(i).normal); %line 67
minim(i).normal=min(imag_etich(i).normal(:))
 hist_etich(i).normal=hist(imag_etich(i).normal(:),0:maxL(i).normal) 
[valmax(i).normal,posmax(i).normal]=max(hist_etich(i).normal(2:end))
etich(i).normal=posmax(i).normal 
M_filt1(i).normal=255*double(imag_etich(i).normal==etich(i).normal);
end 
%% Displayed error
Field assignment to a non-structure array object.
Error in script_sat (line 67) [imag_etich(i).normal, maxL(i).normal]=bwlabel(imag_close(i).normal);

Before this I did a saturation segmentation to obtain the masks, here the mask is M_filt1(i).normal.

I am trying to put some labels on every mask to find every object from the image, so I can scrap the unnecessary pixels outside my lesion. In imag_etich(i).normal I want to save the labeled image, and in maxL(i).normal I wish to save the number of labels from the image.

Help a girl out if you can, pleaase.

Best regards

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Answer 1

Jan 2019-6-21

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https://ww2.mathworks.cn/matlabcentral/answers/468247-how-can-a-code-run-on-a-single-image-perfectly-but-the-same-code-on-an-entire-database-crashes-whe#answer_380250

Use the debugger to find the reason of the problem. Let Matlab stop, when the error occurs:

dbstop if error

Then run the code again until it stops at the error. Then check the used variables:

whos image_etich
whos maxL

One of them is not the assumed struct array and assigning a field must fail.

You do not show how these variables are initialized, so I cannot guess, what exactly the resaon of this behaviour is.

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Andreea Stancu 2019-6-21

I will take it from the begining. My database has 200 images which can be split into three sets, first two sets have 80 images and the third set has 40 images. This is how I loaded the database in the program and how I read the first set (I did the same for the others too)

tabel=readtable('C:\Users\Andreea\Desktop\licenta\PH2Dataset\PH2Dataset\PH2_dataset.xlsx');
tabel(1:11, :) = []; %eliminarea capetelor de tabel
for i=2:size(tabel, 1); 
imag_etich=i; 
poza.nume=tabel(:,1);
end
db=cell2struct(table2array(poza.nume),'nume',200);%obtinerea structurii
for i = 1:size(tabel,1)
    filenames(i).path = sprintf('C:\\Users\\Andreea\\Desktop\\licenta\\PH2Dataset\\PH2Dataset\\PH2_Dataset_images\\%s\\%s_Dermoscopic_Image\\%s.bmp',db(i).nume,db(i).nume,db(i).nume);
end
for i=1:size(filenames,2) %s-a incarcat tabelul excel care continea toate informatiile referitoare la imagini
    imag(i).data=imread(filenames(i).path); 
end
for i = 1:80
    imdb(i).normal = imag(i).data;            
end

Afterwards, I did a segmentation on a saturation threshold like this

for i = 1:80
    procim(i).normal_hsv= rgb2hsv(imdb(i).normal);              
    M1(i).normal=double(255*(procim(i).normal_hsv(:,:,2)>0.5)); 
    M_filt(i).normal=imclose(M1(i).normal, ones(10));           
    M_filt1(i).normal=imopen(M_filt(i).normal, ones(10));i,     
end

And now, I got to the labeling part where I get the error from before:

for i=1:80
imag_open(i).normal=imopen(M_filt1(i).normal, ones(20));
imag_close(i).normal=imclose(imag_open(i).normal, ones(20));
[imag_etich(i).normal, maxL(i).normal]=bwlabel(imag_close(i).normal); 
minim(i).normal=min(imag_etich(i).normal(:))
 hist_etich(i).normal=hist(imag_etich(i).normal(:),0:maxL(i).normal) 
[valmax(i).normal,posmax(i).normal]=maxL(hist_etich(i).normal(2:end))
etich(i).normal=posmax(i).normal 
M_filt1(i).normal=255*double(imag_etich(i).normal==etich(i).normal);
end 

In imag_etich(i).normal there should be the labelled image and in maxL(i).normal, the number of labells found in the picture.

Andreea Stancu 2019-6-21

I did what you suggested and this was the result

 whos imag_etich
  Name            Size            Bytes  Class     Attributes
  imag_etich      1x1                 8  double              
K>> whos maxL

For maxL I don't get anything, it doesn't even appear in the workspace

Jan 2019-6-24

If image_etich is a scalar double, you cannot assign imag_etich(i).normal . Defining the field normal works for structs only.

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Answer 2

Guillaume 2019-6-21

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https://ww2.mathworks.cn/matlabcentral/answers/468247-how-can-a-code-run-on-a-single-image-perfectly-but-the-same-code-on-an-entire-database-crashes-whe#answer_380263

As Jan said you haven't preassigned any of the structures you're using (plus you're also growing your structure arrays in loops, which is not efficient but not relevant to the error). So if any of your structure has been used to store anything else, you'll see the error you get, e.g if at any point you've done:

imag_open = 5;

then

imag_open(i).nomal = ...

will result in the error.

You could solve the problem by creating all your structures at the beginning of your program, e.g.:

imag_open = struct('normal', cell(1, 80));  
%etc, for each structure

which would also create them with the correct size (as long as 80 is the correct size, you're not consistent on that!) and hence avoid the array growing problem as well.

Personally, I'd ditch the structures and simply add variables to your original tables. You also need to learn to manipulate tables. There's rarely any need for table2array. In your case, you need to use {} or . indexing to access the content of the table rather than portions of the table.

Finally, there's a serious problem with your because maxL seems to be use both as a function and variable:

[imag_etich(i).normal, maxL(i).normal] = ...   %maxL is a structure array with one field
%...    
[valmax(i).normal,posmax(i).normal]=maxL(hist_etich(i).normal(2:end))  %maxL used as a function here