Counting coins on a greyscale image - using morphological and/or f transforms

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kandlev
kandlev 2020-11-10
评论： Image Analyst 2020-11-20
I am trying to convert the image into a binary image, using the function form: function C = coins2bw(A) where A is a 2D grayscale image variable and C is a 2D binary image variable. The output image C should show the coins as filled in round disks with no other arifacts or stray foreground pixels(background in black while the coins are white). Using only morphological or fourier transforms.

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Stephan
Stephan 2020-11-10
编辑：Stephan 2020-11-10
I = imread('image.png');
I = imadjust(I);
[centers,radii] = imfindcircles(I,[15 75],'ObjectPolarity','dark','Sensitivity',0.85);
BW = false(size(I,1),size(I,2));
[Xgrid,Ygrid] = meshgrid(1:size(BW,2),1:size(BW,1));
for n = 1:size(centers,1)
BW = BW | (hypot(Xgrid-centers(n,1),Ygrid-centers(n,2)) <= radii(n));
end
maskedImage = I;
maskedImage(~BW) = 0;
imshow(BW)
fprintf('Numbers of coins: %d\n',size(centers,1))
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kandlev
kandlev 2020-11-19
编辑：kandlev 2020-11-19
I don't think so, we're exclusively being asked to use grayscale morphology :(
We were given these dimensions also, but no where in our current study section does it mention 'imfindcircles'.
Could you use a 'disk' structuring element?

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Image Analyst
Image Analyst 2020-11-19
I know you've already accepted an answer and got it solved already, but here's how I'd start:
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
imtool close all; % Close all imtool figures if you have the Image Processing Toolbox.
clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
%===============================================================================
% Read in gray scale image.
folder = pwd;
baseFileName = 'coins.png';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
% Didn't find it there. Check the search path for it.
fullFileName = baseFileName; % No path this time.
if ~exist(fullFileName, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist.', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image. numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(grayImage);
% If it's RGB instead of grayscale, convert it to gray scale.
if numberOfColorBands > 1
grayImage = rgb2gray(grayImage);
end
% Display the original image.
subplot(2, 2, 1);
imshow(grayImage);
axis on;
impixelinfo; % Let user mouse around and see gray level.
caption = sprintf('Original Image : %s', baseFileName);
title(caption, 'FontSize', fontSize);
impixelinfo;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'Outerposition', [0, 0.1, 1, 0.9]);
% Display the histogram
subplot(2, 2, 2);
imhist(grayImage);
grid on;
% Specify a threshold.
threshold = 181
% Place line on histogram at the mean.
xline(threshold, 'Color', 'r', 'LineWidth', 2);
% Create a binary image
mask = grayImage < threshold;
mask = imfill(mask, 'holes');
subplot(2, 2, 3);
imshow(mask);
title('mask', 'FontSize', fontSize);
% Now call imerode to get them to not touch.
% Then call bwlabel to count them.
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kandlev
kandlev 2020-11-20
how do I call bwlabel? I havent used that before. Does it have something to do with one of my requirements? --------->
%required:
A is a coin image and where coinV is a row vector with the following form:
coinV = [Npennies Nnickels Ndimes Nquarters];
Image Analyst
Image Analyst 2020-11-20
Once you have the binary image mask of just the coins, then you do
[labeledImage, numRegions] = bwlabel(mask);
% Then if you want to find all the areas and centroids:
props = regionprops(labeledImage, 'Area', 'Centroid');
allAreas = [props.Area]
xy = vertcat(props.Centroid); % List of centroids' (x, y) coordinates.
See my Image Segmentation Tutorial if you want a well commented tutorial:
Image Analyst's File Exchange

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