how can select a region in image?

hi i need to select a region in image and then save the value of those pixels by using impixel i can choose some pixel by clicking on picture but it is bothersome and i need to select a lot of pixels some function such as imrect dose not get me the value of pixel can you help me please?

Answer 1

[Image Analyst]

I've posted this demo many times before, but here it is again for you. You don't really say what "save the value of those pixels" means to you. They are in a rectangular array - you can use imcrop and imwrite to save out the rectangular array or subarray, or you can get only those pixels selected in some arbitrary region into a 1D list of pixel values and then just leave it saved in the array, or save the 1D list out to a text file or a mat file. You need to be more specific in what "save" means to you.

% Demo to have the user freehand draw an irregular shape over
% a gray scale image, have it extract only that part to a new image,
% and to calculate the mean intensity value of the image within that shape.
% Also calculates the perimeter, centroid, and center of mass (weighted centroid).

% 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));

% 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\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, numberOfPixels1, numberOfPixels2, perimeter, ...
centroid(1), centroid(2), centerOfMass(1), centerOfMass(2));
msgbox(message);

[nadia naji]

i need to save the intensity of pixels in rectangle or each shape.before i use impixel function that return the intensity and position of pixels which are selected but i don't want to click for selecting the pixels because i have a lot of pixels which i should sample them is there any way to solve this problem? if i use function such as imrect or imfreehand, they give me the coordinate of rectangle not intensity of pixels in rectangle. my image are rgb.

[nadia naji]

thanks a lot i use your first idea and use imcrop function.

[Zeynab Mousavikhamene]

I have the boundaries of the image and want to find the pixel intensity in those boundaries. How can I do that?

[David Harrison]

Was this question answered previously? I have tried ginput function, but it only returns the locations of each button click, not the pixel intensity for the area inside the ROI. I have tried impixelregion, which gives me the information I need, but there is no way to save that pixel intensity information for the specified ROI to a matrix to be used later.

[Image Analyst]

If you want the pixels in some boundary/region of an image you can use a binary image that says whether to report that pixel or not.

pixelsInRegion = grayImage(mask);

If you don't have the mask but have a list of boundary coordinates, you can use poly2mask() to get the binary image mask:

mask = poly2mask(x, y, rows, columns);

Answer 2

[Daniell Algar]

Sounds like you want the function imfreehand.

Steve has posted about this befor, see e.g. http://blogs.mathworks.com/steve/2011/01/11/freehand-segmentation-in-the-a-b-plane/.

So has Brett, http://blogs.mathworks.com/steve/2012/12/04/image-effects-part-4/

[nadia naji]

no these function only return position of rectangle but i need the value of pixels in the rectangle.if i also use impixelregion i can not save the value? i need a method that can select an special area in image and save the value of pixels in it

[syafienaz anuar]

do you have solution for this problem? cause i need it too

Answer 3

[molly jane fitches]

I am using Maltab R2015a and it crops up with an error caused by the line: burnedImage(binaryImage) = 255;

I believe this is due to the fact that graphic handles are now objects rather than handles. Any advice on how to get around this?

[Image Analyst]

No, that's not true. The line of code should work. Anyway, burnedImage is NOT a graphics handle - it's a normal 2-D numerical array. You did something not in my demo. I just ran the demo ( my code)in R2017a and it worked beautifully. I can't fix your code (which is different from mine) unless you attach it.