How to save the RGB image after selecting ROI of the image without affecting the original size?

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manami 2019-1-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/440672-how-to-save-the-rgb-image-after-selecting-roi-of-the-image-without-affecting-the-original-size

评论： manami 2019-1-22

I am using the iamge 'peppers.png' whose size is [384*512*3]. After selecting the ROI from the image using the following code, I have saved the image as 'I1'. But the size of the new image 'I1' is [745*1072*3]. How to save the new image with size [384*512*3]? Please help.

I= imread('peppers.png');
ROI=roipoly(I); %select a close polygon
myImage=findall(gcf,'type','image');
set(myImage,'AlphaData',ROI);
saveas(gcf,'newImage.png');
I1=imread('newImage.png');
size(I1)

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Answer 1

Image Analyst 2019-1-21

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https://ww2.mathworks.cn/matlabcentral/answers/440672-how-to-save-the-rgb-image-after-selecting-roi-of-the-image-without-affecting-the-original-size#answer_357342

在 MATLAB Online 中打开

Try this, and note that the sizes are the same:

rgbImage = imread('peppers.png');
ROI = roipoly(rgbImage); % Select a closed polygon
subplot(3, 1, 1);
imshow(rgbImage);
axis('on', 'image');
title('Original Image');
% Mask the image using bsxfun() function to multiply the mask by each channel individually.
maskedRgbImage = bsxfun(@times, rgbImage, cast(ROI, 'like', rgbImage));
whos maskedRgbImage
% Display the masked image.
subplot(3, 1, 2);
imshow(maskedRgbImage);
axis('on', 'image');
title('Masked Image');
% Save the masked image to disk.
imwrite(maskedRgbImage, 'newImage.png');
I2 = imread('newImage.png');
whos I2
% Display the image read in from disk.
subplot(3, 1, 3);
imshow(I2);
axis('on', 'image');
title('Image read In From Disk');