how to find the angle and the sector of the image it belongs in

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JovanS 2022-9-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1807350-how-to-find-the-angle-and-the-sector-of-the-image-it-belongs-in

评论： JovanS 2022-11-4

How can I compute the angle of an image and which of the 8 sectors it belongs in.? i want also for each of the 8 groups of distances I computed, get their standard deviation." I atach a matlab code and the image.

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Matt J 2022-9-18

If you already have code, what needs to be done?

JovanS 2022-9-18

编辑：JovanS 2022-9-18

Actually i have two problems . The fist one is that I don't calculate the angle in the right way and and the other one is that I can't complete the process for sorting distances by angle. I don't know what I have to change in my matlab code in order to fix it.

To be clear , I have to follow this procedure to receive the right results. " compute the Euclidean distance between each boundary coordinate and the centroid. Also compute the angle and which of the 8 sectors it belongs in. For each of the 8 groups of distances you computed, get their standard deviation. If it's more than some predetermined amount, increment the "border" value by one. After all this you will have 8 "border" values. If a sector has a smooth circular shape, it's std dev will be zero, and the std dev will increase the more tortuous the border is." @Matt J

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Answer 1

Image Analyst 2022-9-18

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1807350-how-to-find-the-angle-and-the-sector-of-the-image-it-belongs-in#answer_1055775

在 MATLAB Online 中打开

@Ioanna St try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 15;
%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = 'color_wh.jpg'; % Assign the one on the button that they clicked on.
% Get the full filename, with path prepended.
folder = []; % Determine where demo folder is (works with all versions).
fullFileName = fullfile(folder, baseFileName);
%===============================================================================
% Read in a demo image.
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
    grayImage = rgb2gray(grayImage);
end
% Display the image.
subplot(2, 2, 1);
imshow(grayImage, []);
axis on;
caption = sprintf('Original Gray Scale Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo();
% Maximize figure window:
g = gcf;
g.WindowState = 'maximized';
drawnow;
% Binarize the image by thresholding.
binaryImage = grayImage<100;
% Get rid of white surround.
binaryImage = imclearborder(binaryImage);
% Extract the largest blob only.
binaryImage = bwareafilt(binaryImage, 1);
% Fill holes.
binaryImage=imfill(binaryImage,'holes');
% Display the image.
subplot(2, 2, 2);
imshow(binaryImage);
impixelinfo
axis on;
title('Binary Image', 'fontSize', fontSize);
drawnow;
% Label the image
labeledImage = bwlabel(binaryImage);
% Make the measurements
props = regionprops(labeledImage, grayImage, 'Centroid', 'WeightedCentroid');
xCentroid = props.Centroid(1)
yCentroid = props.Centroid(2)
%  Find the half way point of the image.
middlex = columns/2;
middley = rows/2;
% Plot a + at the center of the blob and center of the image.
hold on;
yline(middley, 'Color', 'm', 'LineWidth', 2);
xline(middlex, 'Color', 'm', 'LineWidth', 2);
plot(xCentroid, yCentroid, 'r+', 'LineWidth', 2, 'MarkerSize', 30);
title('Binary Image with centers found', 'fontSize', fontSize);
% Display the image.
subplot(2, 2, 3);
imshow(grayImage);
axis on;
title('Gray Image with centroid marked', 'fontSize', fontSize);
% Plot a + at the center of the blob and center of the image.
hold on;
yline(middley, 'Color', 'm', 'LineWidth', 2);
xline(middlex, 'Color', 'm', 'LineWidth', 2);
plot(xCentroid, yCentroid, 'r+', 'LineWidth', 2, 'MarkerSize', 30);
drawnow;
% Compute center of mass, though user doesn't actually use it.
% centerOfMass = props.WeightedCentroid
% Find boundaries.
[B, L] = bwboundaries(binaryImage, 'noholes');
subplot(2, 2, 4);
imshow(grayImage);
title('Boundaries of the Image', 'fontSize', fontSize);
% Draw boundaries over the image.
hold on
numberOfRegions = numel(B)
for k = 1 : numberOfRegions % Should be just one boundary because we used bwareafilt
    thisBoundary = B{k};
    xB = thisBoundary(:,2);
    yB = thisBoundary(:,1);
    plot(thisBoundary(:,2), thisBoundary(:,1), 'b', 'LineWidth', 2)
end
numberOfSectors = 8; % I want to divide the image in 8 sectors
sectorAngleLimits = linspace(-180, 180, numberOfSectors + 1)
%border=0;
caDistances = cell(numberOfSectors,1);
for k = 1:numberOfRegions % Should be just one boundary because we used bwareafilt
    thisBoundary = B{k};
    xB = thisBoundary(:,2);
    yB = thisBoundary(:,1);
    distances = sqrt((xCentroid-xB).^2+(yCentroid-yB).^2);
    % Find the angle in radians from centroid of every point in the border.
    [angles, rho] = cart2pol((xB - xCentroid), (yB - yCentroid));
    % Note: rho should equal distances.
    % Convert angles to degrees.
    angles = ((angles/(pi*2)) * 360);
    % Alternate way.
    %     slopes = (yB - yCentroid) ./ (xB - xCentroid);
    %     angles =atand(slopes)
    % Get distances for each sector
    for ks = 1 : numberOfSectors
        angleMask = angles >= sectorAngleLimits(ks) & angles < sectorAngleLimits(ks + 1);
        distancesWithinEachSector{ks} = distances(angleMask);
    end
end
distancesWithinEachSector
figure;
% Determine if the distances vary widely.
borderValue = zeros(1, numberOfSectors);
for c = 1 : numberOfSectors
    thisSectorsDistances = distancesWithinEachSector{c};
    subplot(3, 3, c);
    histogram(thisSectorsDistances);
    grid on;
    caption = sprintf('Distance Distribution for Sector #%d', c);
    title(caption, 'FontSize',fontSize)
    stddev = std(thisSectorsDistances);
    % Determine if it's big.
    if stddev > 30       % sto paper anaferei oti threshold is set empirically to 30
        borderValue(c) = 1;
    end
end
borderValue
% Maximize figure window:
g2 = gcf;
g2.WindowState = 'maximized';

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Image Analyst 2022-9-19

在 MATLAB Online 中打开

For 1, that's just normal masking like you learned when you first learned MATLAB. For example to get all numbers between 4 and 9 if the vector is -179:180 you do

v = -179:180
v = 1×360
  -179  -178  -177  -176  -175  -174  -173  -172  -171  -170  -169  -168  -167  -166  -165  -164  -163  -162  -161  -160  -159  -158  -157  -156  -155  -154  -153  -152  -151  -150
mask =  v >= 4 & v <= 9 % A logical vector.
mask = 1×360 logical array
   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   1   1   1   1   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
extractedValues = v(mask) % Selected angles.
extractedValues = 1×6
     4     5     6     7     8     9
distances = 1000 * randi(9, 1, length(v)) % Sample values.
distances = 1×360
        6000        9000        9000        9000        7000        3000        2000        4000        9000        2000        6000        8000        2000        6000        7000        8000        9000        3000        1000        6000        3000        3000        5000        2000        1000        8000        4000        3000        7000        8000
extractedDistances = distances(mask)
extractedDistances = 1×6
        9000        8000        1000        4000        8000        9000

I think it looks like the std follows your equation.

Image Analyst 2022-11-4

在 MATLAB Online 中打开

test7.m

Simply plot it to see what sector is where:

for ks = 1 : numberOfSectors
    angleMask = angles >= sectorAngleLimits(ks) & angles < sectorAngleLimits(ks + 1);
    ph = plot(xB(angleMask), yB(angleMask), 'r-', 'LineWidth', 3)
    message = sprintf('This is sector #%d', ks);
    reply = questdlg(message, 'Continue', 'Yes', 'No', 'Yes');
    delete(ph);
    if strcmpi(reply, 'No')
        return;
    end
    distancesWithinEachSector{ks} = distances(angleMask);
end

Full demo attached.

JovanS 2022-11-4

Thank you!!

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