Remove white padding from image

Question

YT 2018-10-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423864-remove-white-padding-from-image

评论： Nate Roberts 2020-4-1

test-image.jpg

I want to remove white padding from an image (see attachment). The size of the padding is random.

So I was thinking of reading in the image and then some looping to check if the entire row/column contains the value 255. However, looping is most of the time not the best way to do stuff. So I'm wondering if there's an easier way to do this, because I've found a similar question where the rows/columns contain 0, but I don't know if this can also be used for this case (with some adjustments).

Thanks in advance.

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Answer 1

Walter Roberson 2018-10-14

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https://ww2.mathworks.cn/matlabcentral/answers/423864-remove-white-padding-from-image#answer_341301

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I = imread('test-image.jpg');
W = all(I == 255, 3);
maskc = all(W, 1);
maskr = all(W, 2);
J = I;
J(maskr,:,:) = 0;
J(:,maskc,:) = 0;
image(J)

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Walter Roberson 2018-10-14

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"remove white padding" is ambiguous as to whether it should be transformed to a different color or cropped out of the image.

I = imread('test-image.jpg');
W = all(I == 255, 3);
maskc = ~all(W, 1);
maskr = ~all(W, 2);
J = I(maskr, maskc);
imshow(IM);

Nate Roberts 2020-4-1

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This is exactly what I was looking for. I made a little script that can do this for an RBG image, assuming you only want to remove the padding, and not the white space within an image.

function im2 = removeWhitePadding(im1, dim)
    if nargin<2
        dim = 0;
    end
    WhitePixels = all(im1 == 255, 3);
    maskr = ~all(WhitePixels, 2);
    maskc = ~all(WhitePixels, 1);
    
    if dim==1
        im2 = im1(find(maskr, 1, 'first'):find(maskr, 1, 'last'),:,:);
    elseif dim==2
        im2 = im1(:,find(maskc, 1, 'first'):find(maskc, 1, 'last'),:);
    else
        im2 = im1(find(maskr, 1, 'first'):find(maskr, 1, 'last'),find(maskc, 1, 'first'):find(maskc, 1, 'last'),:);
    end
end

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Answer 2

Image Analyst 2018-10-14

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https://ww2.mathworks.cn/matlabcentral/answers/423864-remove-white-padding-from-image#answer_341343

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Try this:

rgbImage = imread('test-image.jpg');
subplot(2, 2, 1);
imshow(rgbImage);
title('Original RGB Image', 'FontSize', 20);
axis('on', 'image');
nonWhitePixels = any(rgbImage ~= 255, 3);
subplot(2, 2, 2);
imshow(nonWhitePixels)
title('Non-white Pixels Mask', 'FontSize', 20);
axis('on', 'image');
[maskRows, maskColumns] = find(nonWhitePixels);
% Crop image
croppedImage = rgbImage(min(maskRows):max(maskRows), min(maskColumns):max(maskColumns), :);
subplot(2, 2, 3);
imshow(croppedImage);
axis('on', 'image');
title('Cropped RGB Image', 'FontSize', 20);