I want to lower the contrast at particular locations in an image but not the whole image. Is there any way to change it just by clicking some places on image and giving our desired grey color without specifying coordinate points??
MATLAB: How can i change the contrast at few locations in an image
image processingImage Processing Toolbox
Related Solutions
imfreehand() perhaps? See http://www.mathworks.com/help/images/building-guis-with-modular-interactive-tools.html
You can use imfreehand. Then mask your image before or after your operations with a binary image defined by imfreehand. Here is a demo if you need one:
% 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)));endclc; % 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; endendgrayImage = 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.Areacentroid = measurements.CentroidcenterOfMass = measurements.WeightedCentroidperimeter = 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 masshold 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);
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