Binary Image: Count number of pixels that are 1.

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Justine Schneider
评论： Image Analyst 2022-2-1
The code below is a simplified version of the one part of a longer code that I am running into an error. In the code below, I successfully convert the gray scale image into a binary image. Then I try to count the number of pixels in the image that are 1 (by using the for loop and bin()). However, MATLAB says, "Undefined function or variable 'rows'." Then if I type a number instead of saying rows columns, I get the error, "if bin(i,j) == 1."
I've looked at the syntax of the bin command, and I have tried problem solving this. However, I don't know if the for loop knows to apply itself to the image. Please let me know how I can fix this for loop to work properly.
Code:
I = imread('rice.png');
figure; imshow(I);
bw = imbinarize(I);
figure; imshow(bw);
ctr= 0;
for i = 1 : rows
for j = 1 : columns
if bin(i,j) == 1
ctr = ctr + 1;
end
end
end

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2017-7-3
May be so:
I = imread('rice.png');
figure; imshow(I);
bw = imbinarize(I);
figure; imshow(bw);
ctr= 0;
for i = 1 : rows
for j = 1 : columns
if bw(i,j) == 1
ctr = ctr + 1;
end
end
end
  8 个评论
显示 6更早的评论
oussama zayene
oussama zayene 2022-2-1
Hi shan shan,
Did you resolve this, if yes can you please share the code ?
Thanks
Image Analyst
Image Analyst 2022-2-1
I'm sure that after almost 2 years he did. It probably went something like this:
props = regionprops(bw, 'BoundingBox');
for k = 1 : numel(props)
thisBB = props(k).BoundingBox;
croppedImage = imcrop(bw, thisBB);
% Now do something with cropped image.....
end

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更多回答（4 个）

Jan
Jan 2017-7-3
Alternatively without a loop:
bw = imbinarize(I);
ctr = sum(bw(:) == 1);
or even shorter for a binary image:
ctr = sum(bw(:));
James Tursa
James Tursa 2020-4-6
nnz(bw)
Image Analyst
Image Analyst 2018-2-4
编辑：Image Analyst 2022-2-1
If you want to know why your code didn't work, the problem with your code is that you forgot to define rows and columns for your image. After imread(), you need this:
[rows, columns, numberOfColorChannels] = size(I);
But better, like Jan said, you can simply could the number of white/true/1 pixels with this:
numWhite = sum(BW(:)) % numWhite is what you called ambiguously called ctr ("counter", "centroid"?)
No nested for loop is even needed.
Or even better is @James Tursa's answer:
numWhite = nnz(bw);
bipul
bipul 2018-9-23
编辑：bipul 2018-9-23
function ctr = PixelCounter(bw)
%I = imread('rice.png');
%I = I(4:15, 18:29);
%figure; imshow(I);
%bw = im2bw(I)
%figure; imshow(bw);
ctr= 0;
[rows columns] = size(bw);
for i = 1 : rows
for j = 1 : columns
if bw(i,j) == 1
ctr = ctr + 1;
end
end
end
%fprintf('1 are: %d \n', ctr);
%disp(ctr);
end

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