How to solve "brace indexing is not supported for variables of this type" for this code?

Question

Tawsif Mostafiz 2021-5-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/838720-how-to-solve-brace-indexing-is-not-supported-for-variables-of-this-type-for-this-code

编辑： Image Analyst 2021-5-25

Excerpt of my code is as follows:

s=0;
for k = 1 : length(theFiles)
	for q=0.1:0.01:0.3
		histgrm=im2bw(maskedRgbImage,q);
		num{k}=sum(histgrm(:) == 0);
		if(num{k}>400)
			number{s}=num{k};
			s=s+1;
		end
	end
end
for s=0:19
	fprintf("%d\n",number{s})
end

length(theFiles), histgrm are defined in the original code. But it shows error as:

Unable to perform assignment because brace indexing is not supported for variables of this type.

How can I fix this?

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Tawsif Mostafiz 2021-5-25

Sorry for being vague.

class(num) = 'cell'

class(number) = "double'

DGM 2021-5-25

在 MATLAB Online 中打开

then just use

number(s)

instead of

number{s}

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Answer 1

Image Analyst 2021-5-25

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/838720-how-to-solve-brace-indexing-is-not-supported-for-variables-of-this-type-for-this-code#answer_707930

在 MATLAB Online 中打开

No need for cell arrays, which use braces. Use just regular double arrays with parentheses:

		num(k) = sum(histgrm(:) == 0);
		if(num(k)>400)
			number(s) = num(k);

I think it's also deceptive to name a binary image "histgrm" which leads the reader to think it's a histogram instead of a binary image outputted from im2bw().

Next you need to initialize s to 1 instead of zero because there is no zeroth element in MATLAB.

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Tawsif Mostafiz 2021-5-25

在 MATLAB Online 中打开

@Image Analyst when I do it, this shows:

Conversion to cell from double is not possible.

histgrm is defined as:

histgrm=im2bw(maskedRgbImage,q);

Image Analyst 2021-5-25

编辑：Image Analyst 2021-5-25

在 MATLAB Online 中打开

Nowhere in my code do I convert a cell to a double. The output of im2bw() is a logical -- a binary image though you deceptively called it a histogram. Nowhere did I even use braces to address it as a double. See the very first item on the FAQ to get an appreciation of what cell arrays are and when to use braces, parentheses, and brackets:

https://matlab.fandom.com/wiki/FAQ#What_is_a_cell_array.3F

There is just so much wrong with your code I don't want to explain every thing I fixed, just see this fixed code below:

theFiles = dir('*.png');
allQs = 0.1 : 0.01 : 0.3;
numqs = length(allQs);
numFiles = length(theFiles);
number = zeros(numqs, numFiles);
for k = 1 : numFiles
	fullFileName = fullfile(theFiles(k).folder, theFiles(k).name);
	grayImage = imread(fullFileName);
	subplot(2, 1, 1);
	imshow(grayImage);
	caption = sprintf('#%d of %d : "%s"', k, numFiles, theFiles(k).name);
	title(caption, 'Interpreter', 'none');
	[rows, columns, numberOfColorChannels] = size(grayImage);
	if numberOfColorChannels > 1
		% Convert to gray scale.
		grayImage = rgb2gray(grayImage);
	end
	for k2 = 1 : numqs
		q = allQs(k2);
		binaryImage = imbinarize(grayImage, q);
		subplot(2, 1, 2);
		imshow(binaryImage);
		caption = sprintf('q = %.2f', q);
		title(caption, 'Interpreter', 'none');
		drawnow;
		numZeros = nnz(~binaryImage);
		% If there are more than 400 pixels above the threshold, log it.
		if(numZeros > 400)
			number(k2, k) = numZeros;
		end
	end
	% Print out the values for this image.
	fprintf('For %s, number = \n    ', theFiles(k).name);
	for k2 = 1 : numqs
		fprintf("%d ", number(:, k))
	end
	fprintf('\n');
end
figure
imshow(number, []);