How to isolate certain part of image?
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Umme Tania
el 6 de Sept. de 2013
Comentada: Image Analyst
el 1 de Sept. de 2020
Suppose i have a eye image, in that image i draw a circle. Now i want to isolate the circle part from the rest of image.
1 comentario
Susanna Moore
el 4 de Mzo. de 2014
For my view, to just isolate and obtain the image circle part, you can use a third-party image processing library (free trial).Generally, you can easily crop the part.
Respuesta aceptada
Image Analyst
el 1 de Oct. de 2013
Editada: Image Analyst
el 2 de Oct. de 2013
All right, I have one expecially for circles that's simpler than the other one (which perhaps was ignored because its length scared you off). Don't worry - the main code in this is only one line long. Mostly it's long because of all the comments and fancy things like displaying images and giving titles to them. The main line of code is this:
maskedImage(~circleImage) = 0; % Zero image outside the circle mask.
Which you can change to
maskedImage(~circleImage) = 255; % Whiten image outside the circle mask.
if you want white instead of black.
Try this demo (also attached):
% Demo to mask an image with a circle.
% Requires the Image Processing Toolbox.
%
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
imtool close all; % Close all imtool figures.
clear; % Erase all existing variables.
workspace; % Make sure the workspace panel is showing.
fontSize = 20;
% Change the current folder to the folder of this m-file.
if(~isdeployed)
cd(fileparts(which(mfilename)));
end
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
% Comment out whichever demo image you don not want to use.
baseFileName = 'cameraman.tif'; % Grayscale demo image.
baseFileName = 'peppers.png'; % Color demo image.
fullFileName = fullfile(folder, baseFileName);
% See if the image exists.
if ~exist(fullFileName, 'file')
% Doesn't exist in that folder. See if it exists anywhere on the path.
fullFileName = baseFileName;
if ~exist(fullFileName, 'file')
errorMessage = sprintf('Error: file %s not found', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
% Read in the image from disk.
originalImage = imread(fullFileName);
% Get the dimensions of the image. numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(originalImage);
% Display the original gray scale image.
subplot(2, 2, 1);
imshow(originalImage, []);
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Original Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Position', get(0,'Screensize'));
set(gcf,'name','Image Analysis Demo','numbertitle','off')
% Initialize parameters for the circle,
% such as it's location and radius.
circleCenterX = 130;
circleCenterY = 75; % square area 0f 500*500
circleRadius = 50; % big circle radius
% Initialize an image to a logical image of the circle.
circleImage = false(rows, columns);
[x, y] = meshgrid(1:columns, 1:rows);
circleImage((x - circleCenterX).^2 + (y - circleCenterY).^2 <= circleRadius.^2) = true;
% Display it in the upper right plot.
subplot(2,2,2);
imshow(circleImage, []);
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Circle Mask', 'FontSize', fontSize);
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
drawnow;
% Mask the image with the circle.
if numberOfColorBands == 1
maskedImage = originalImage; % Initialize with the entire image.
maskedImage(~circleImage) = 0; % Zero image outside the circle mask.
else
% Mask the image.
maskedImage = bsxfun(@times, originalImage, cast(circleImage,class(originalImage)));
end
% Display it in the lower right plot.
subplot(2, 3, 5);
imshow(maskedImage, []);
% Change imshow to image() if you don't have the Image Processing Toolbox.
title('Image masked with the circle.', 'FontSize', fontSize);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/172189/image.jpeg)
14 comentarios
Image Analyst
el 1 de Sept. de 2020
Call drawrectangle(), imrect(), or rbbox() to get the rows and columns of the box.
Más respuestas (2)
Image Analyst
el 6 de Sept. de 2013
See my masking demo. You should be able to adapt it to do what you want. Let me know if you can't.
% Demo to have the user freehand draw an irregular shape over a gray scale image.
% Then it creates new images:
% (1) where the drawn region is all white inside the region and untouched outside the region,
% (2) where the drawn region is all black inside the region and untouched outside the region,
% (3) where the drawn region is untouched inside the region and all black outside the region.
% It also (4) calculates the mean intensity value and standard deviation of the image within that shape,
% (5) calculates the perimeter, centroid, and center of mass (weighted centroid), and
% (6) crops the drawn region to a new, smaller separate image.
% Change the current folder to the folder of this m-file.
if(~isdeployed)
cd(fileparts(which(mfilename)));
end
clc; % Clear command window.
clear; % Delete all variables.
close all; % Close all figure windows except those created by imtool.
imtool close all; % Close all figure windows created by imtool.
workspace; % Make sure the workspace panel is showing.
fontSize = 16;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cameraman.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
% File doesn't exist -- 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 in the search path folders.', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
grayImage = imread(fullFileName);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize);
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
message = sprintf('Left click and hold to begin drawing.\nSimply lift the mouse button to finish');
uiwait(msgbox(message));
hFH = imfreehand();
% Create a binary image ("mask") from the ROI object.
binaryImage = hFH.createMask();
xy = hFH.getPosition;
% Now make it smaller so we can show more images.
subplot(2, 3, 1);
imshow(grayImage, []);
axis on;
drawnow;
title('Original Grayscale Image', 'FontSize', fontSize);
% Display the freehand mask.
subplot(2, 3, 2);
imshow(binaryImage);
axis on;
title('Binary mask of the region', 'FontSize', fontSize);
% Label the binary image and computer the centroid and center of mass.
labeledImage = bwlabel(binaryImage);
measurements = regionprops(binaryImage, grayImage, ...
'area', 'Centroid', 'WeightedCentroid', 'Perimeter');
area = measurements.Area
centroid = measurements.Centroid
centerOfMass = measurements.WeightedCentroid
perimeter = measurements.Perimeter
% Calculate the area, in pixels, that they drew.
numberOfPixels1 = sum(binaryImage(:))
% Another way to calculate it that takes fractional pixels into account.
numberOfPixels2 = bwarea(binaryImage)
% Get coordinates of the boundary of the freehand drawn region.
structBoundaries = bwboundaries(binaryImage);
xy=structBoundaries{1}; % Get n by 2 array of x,y coordinates.
x = xy(:, 2); % Columns.
y = xy(:, 1); % Rows.
subplot(2, 3, 1); % Plot over original image.
hold on; % Don't blow away the image.
plot(x, y, 'LineWidth', 2);
drawnow; % Force it to draw immediately.
% Burn line into image by setting it to 255 wherever the mask is true.
burnedImage = grayImage;
burnedImage(binaryImage) = 255;
% Display the image with the mask "burned in."
subplot(2, 3, 3);
imshow(burnedImage);
axis on;
caption = sprintf('New image with\nmask burned into image');
title(caption, 'FontSize', fontSize);
% Mask the image and display it.
% Will keep only the part of the image that's inside the mask, zero outside mask.
blackMaskedImage = grayImage;
blackMaskedImage(~binaryImage) = 0;
subplot(2, 3, 4);
imshow(blackMaskedImage);
axis on;
title('Masked Outside Region', 'FontSize', fontSize);
% Calculate the mean
meanGL = mean(blackMaskedImage(binaryImage));
sdGL = std(double(blackMaskedImage(binaryImage)));
% Put up crosses at the centriod and center of mass
hold on;
plot(centroid(1), centroid(2), 'r+', 'MarkerSize', 30, 'LineWidth', 2);
plot(centerOfMass(1), centerOfMass(2), 'g+', 'MarkerSize', 20, 'LineWidth', 2);
% Now do the same but blacken inside the region.
insideMasked = grayImage;
insideMasked(binaryImage) = 0;
subplot(2, 3, 5);
imshow(insideMasked);
axis on;
title('Masked Inside Region', 'FontSize', fontSize);
% Now crop the image.
leftColumn = min(x);
rightColumn = max(x);
topLine = min(y);
bottomLine = max(y);
width = rightColumn - leftColumn + 1;
height = bottomLine - topLine + 1;
croppedImage = imcrop(blackMaskedImage, [leftColumn, topLine, width, height]);
% Display cropped image.
subplot(2, 3, 6);
imshow(croppedImage);
axis on;
title('Cropped Image', 'FontSize', fontSize);
% Put up crosses at the centriod and center of mass
hold on;
plot(centroid(1)-leftColumn, centroid(2)-topLine, 'r+', 'MarkerSize', 30, 'LineWidth', 2);
plot(centerOfMass(1)-leftColumn, centerOfMass(2)-topLine, 'g+', 'MarkerSize', 20, 'LineWidth', 2);
% Report results.
message = sprintf('Mean value within drawn area = %.3f\nStandard deviation within drawn area = %.3f\nNumber of pixels = %d\nArea in pixels = %.2f\nperimeter = %.2f\nCentroid at (x,y) = (%.1f, %.1f)\nCenter of Mass at (x,y) = (%.1f, %.1f)\nRed crosshairs at centroid.\nGreen crosshairs at center of mass.', ...
meanGL, sdGL, numberOfPixels1, numberOfPixels2, perimeter, ...
centroid(1), centroid(2), centerOfMass(1), centerOfMass(2));
msgbox(message);
8 comentarios
Shyme Bhate
el 1 de Abr. de 2020
@Image Analyst, please help me in this issue, I am so worried. I just want to separate both the parts (tumorous and non-tumoros) from MRI and save separetly both parts.
Image Analyst
el 1 de Abr. de 2020
Editada: Image Analyst
el 1 de Abr. de 2020
Why is your MRI image in color? MRI images are normally grayscale. Did you get one that was already marked up/annotated somehow? If so, make sure you get original gray scale images.
For an automatic method, see my attached example where it segments the tumor based on intensity.
Ashutosh
el 6 de Sept. de 2013
Umme, do you want to create a separate image with just the part within the circle and everything else as black?
4 comentarios
Ashutosh
el 8 de Dic. de 2013
put the coordinates of the point to the equation of a circle centred at a,b and test for values to be less than or equal to zero. The point within the circle will have a negative value for eqn.
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