I would like to know how to superimpose images in MATLAB.
% Create the background % This example uses a blend of colors from left to right, converted to a TrueColor image % Use repmat to replicate the pattern in the matrix % Use the "jet" colormap to specify the color space bg = ind2rgb(repmat(1:64,64,1),jet(64)); % Create an image and its corresponding transparency data % This example uses a random set of pixels to create a TrueColor image im = rand(100,100,3); % Make the image fade in from left to right by designing its alphadata % Use repmat to replicate the pattern in the transparency fading imAlphaData = repmat(0:1/size(im,2):1-1/size(im,2),size(im,1),1); % Display the images created in subplots hf = figure('units','normalized','position',[.2 .2 .6 .6]); ax1 = subplot(2,3,1); ibg = image(bg); axis off title('Background') ax2 = subplot(2,3,4); iim = image(im); axis off title('Image without transparency yet') % Now set up axes that overlay the background with the image % Notice how the image is resized from specifying the spatial % coordinates to locate it in the axes. ax3 = subplot(2,3,[2:3, 5:6]); ibg2 = image(bg); axis off hold on % Overlay the image, and set the transparency previously calculated iim2 = image(im,'XData',[30 50],'YData',[10 30]); set(iim2,'AlphaData',imAlphaData); title(sprintf('Using transparency while overlaying images:\nresult is multiple image objects.'))
If you want to extract a circle from the image, and overlay just that (NOTE: This part of the example requires the Image Processing Toolbox function ROIPOLY to create the circle mask.):
% Add another image to the background, but use the 'AlphaData' property % to just overlay a circle instead. % % First define the polygon region of interest t = 0:.1:2*pi; [imheight,imwidth] = size(im(:,:,1)); x = round(20*cos(t)+round(imwidth/2)); y = round(20*sin(t)+round(imheight/2)); % Extract the polygon mask imCircleAlphaData = roipoly(im,x,y); axes(ax3); % Overlay the image, and set the transparency previously calculated iim3 = image(im,'XData',[0 30],'YData',[30 60]); set(iim3,'AlphaData',double(imCircleAlphaData));
2. Using indexing to superimpose images: Use this method if you have an image that you want to place in a scene, but prefer to have only a single image as a resultant. The following example achieves this by replacing the scene pixels with the object image pixels.
% Create the scene % This example uses a random set of pixels to create a TrueColor image scene = rand(100,100,3); % Create the object image % This example uses a blend of colors from left to right, converted to a TrueColor image % Use repmat to replicate the pattern in the matrix % Use the "jet" colormap to specify the color space obj = ind2rgb(repmat(1:64,64,1),jet(64)); % Display the images created in subplots hf2 = figure('units','normalized','position',[.2 .2 .6 .6]); axi1 = subplot(2,3,1); iscene = image(scene); axis off title('Scene') axi2 = subplot(2,3,4); iobj = image(obj); axis off title('Object image') % Now replace pixels in the scene with the object image result = scene; % Define where you want to place the object image in the scene rowshift = 20; colshift = 0; % Perform the actual indexing to replace the scene's pixels with the object result((1:size(obj,1))+rowshift, (1:size(obj,2))+colshift, :) = obj; % Display the results ax3 = subplot(2,3,[2:3, 5:6]); iresult = image(result); axis off hold on title(sprintf('Using indexing to overlay images:\nresult is one image object'))
If you want to extract a circle from the object, and overlay just that: (AGAIN, NOTE: This part of the example requires the Image Processing Toolbox function ROIPOLY to create the circle mask.):
% Let's add another image to the scene. % First define the polygon region of interest t = 0:.1:2*pi; [objheight,objwidth] = size(obj(:,:,1)); x = round(20*cos(t)+round(objwidth/2)); y = round(20*sin(t)+round(objheight/2)); % Since the mask is 2D, repeat it through the 3D RGB matrix % while extracting the polygon mask objCircleMask = repmat(roipoly(obj,x,y),[1,1,3]); % Define where we want to place the circle object in the scene rowshift = 0; colshift = 30; result2 = result; % Perform the actual indexing. First calculate the replacement pixels % by multiplying the scene by the negative of the mask, and then adding % the object multiplied by the mask. Multiplying the mask chooses all % pixels corresponding to a 1 in the mask, and removes color from the % pixels corresponding to a 0. replacementPixels = ( result((1:size(obj,1))+rowshift, (1:size(obj,2))+colshift, :) ... .* double(~objCircleMask) ) + ( obj .* double(objCircleMask) ); % Now replace the pixels with the ones we just calculated result2((1:size(obj,1))+rowshift, (1:size(obj,2))+colshift, :) = replacementPixels; % Display the results. Notice that we placed the circle object in the scene % that resulted from the previous object placement. axes(ax3); delete(iresult) iresult2 = image(result2);
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