How to choose a ROI of an image and make rest transparent, then save it?
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I have two images of the same object: 1) bright-field, 2) a luminescence intensity. To create an overlay, I would like to define a ROI of the image 2), and then overlay this to the image 1). The area outside of ROI in image 2) should be transparent.
I got the ROI working and it also displays as the region outside of the ROI is transparent, but then exporting/saving fails
I=imread('cameraman.tif');
I=double(I); %convert to my typical form of input
% Define the Region of Interest
c = [100 200 200 100];
r = [100 100 200 200];
% Creates a Mask
BW = roipoly(I,c,r);
BW = double(BW);
BW(BW==0) = NaN; %set elements outside to NaN
filter_1 = I.*BW; % multipliy to get old intensity
image(filter_1);
transparent=image(I, 'AlphaData', filter_1);
imwrite(I, 'test.png', 'Alpha', filter_1) %doesn't work
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Thiago Henrique Gomes Lobato
2019-12-15
To write the image I has to be either a double normalized to 1 or a uint8 with values from 0 to 255, in your case you had double values from 0 to 255. Alpha also has to be between 0 and 1. Changing just the last line of your code produces the results that you want
imwrite(uint8(I), 'test.png', 'Alpha', filter_1/max(filter_1(:)))
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更多回答(1 个)
Pascal Gschwend
2019-12-15
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Image Analyst
2019-12-15
You can convert your indexed image to an RGB image before saving, but you don't have to. You can save indexed images along with their colormaps. See the code below:
grayImage = imread('moon.tif');
cmap = hsv(256);
imshow(grayImage, 'Colormap', cmap);
colorbar
% Save indexed image along with it's color map to disk.
imwrite(grayImage, cmap, 'deleteme.tif');
% Read it back in and apply the colormap and observe it looks the same.
figure
[grayImage2, cmap2] = imread('deleteme.tif');
imshow(grayImage2, 'Colormap', cmap2); % Looks exactly the same
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