Outline the shape in the image

Question

Hassan Strong 2020-5-31

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评论： Image Analyst 2021-8-31

Hi,

I need to outline a shape with circle in the image. Here is the image which i created using colormap.

The condition is if the 0.6<pixel<1 , then outline it with a circle. where pixel is the pixel value which is ranged from 0.1 to 1.

Here is the image info

Filename: XXXXX

FileModDate: '31-May-2020 23:43:42'

FileSize: 1588399

Format: 'tif'

FormatVersion: []

Width: 840

Height: 630

BitDepth: 24

ColorType: 'truecolor'

FormatSignature: [73 73 42 0]

ByteOrder: 'little-endian'

NewSubFileType: 0

BitsPerSample: [8 8 8]

Compression: 'Uncompressed'

PhotometricInterpretation: 'RGB'

StripOffsets: [1×70 double]

SamplesPerPixel: 3

RowsPerStrip: 9

StripByteCounts: [1×70 double]

XResolution: 96

YResolution: 96

ResolutionUnit: 'Inch'

Colormap: []

PlanarConfiguration: 'Chunky'

TileWidth: []

TileLength: []

TileOffsets: []

TileByteCounts: []

Orientation: 1

FillOrder: 1

GrayResponseUnit: 0.0100

MaxSampleValue: [255 255 255]

MinSampleValue: [0 0 0]

Thresholding: 1

Offset: 1587608

ImageDescription: 'MATLAB Handle Graphics'

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Answer 1

Image Analyst 2020-6-1

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You can use bwboundaries() and plot():

binaryImage =  0.6 < grayImage & grayImage < 1;
boundaries = bwboundaries(binaryImage);
hold on;
for k = 1 : length(boundaries)
    thisBoundary = boundaries{k};
    x = thisBoundary(:, 2); % Column
    y = thisBoundary(:, 1); % Row
    plot(x, y, 'r-', 'LineWidth', 2);
end

Attach your array or image file if you need more help.

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Alex Perrakis 2021-8-31

Hey, is there a way to plot those lines in normal plot with x-y-coordinates? i have your solution and i have found very good success thanks

Image Analyst 2021-8-31

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@Alex Perrakis, yes, simply bring up a new axes - one that does not have an image it in already - and call the same code

binaryImage =  0.6 < grayImage & grayImage < 1;
boundaries = bwboundaries(binaryImage);
figure; % Create a new figure.
for k = 1 : length(boundaries)
    thisBoundary = boundaries{k};
    x = thisBoundary(:, 2); % Column
    y = thisBoundary(:, 1); % Row
    plot(x, y, 'r-', 'LineWidth', 2);
end
grid on;

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Answer 2

Codeshadow 2020-6-1

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编辑：Codeshadow 2020-6-1

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You could try using contourf and specify the contour levels as an input argument.

For example:

% Create an example mesh
x = linspace(-1, 1, 100);
y = x;
[X, Y] = meshgrid(x, y);
% Compute the radii
R = sqrt(X.^2 + Y.^2);
% Generate contour map, with levels in increments of 0.1 or at a fixed value
% level = [0:0.1:1];
level = [0.6 0.6];
contourf(X, Y, R, level)
colorbar();
xlabel('X')
ylabel('Y');

Replace R used above with your data.

Note: You might not be placing a circle around your data, but will instead be tracing the isolines at the levels you desire.

Hope this helps!

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Codeshadow 2020-6-1

Apologies, I'd made a typo in my original answer, and have fixed it now.

When specifying a single level in the contourf function, you will need to pass it in as a vector of two identical values, such as [0.6 0.6] in the corrected code above. If you want to plot several levels, you can specify all levels in a vector (see commented code).

For the example of the circle, if you specify a level as [0.6 0.6], you will get something like

You can use the Key-Value pair argument ('ShowText', 'on') to mark the levels if you'd like.

Hassan Strong 2020-6-1