Backgroud Added to images after imwrap transformations

Question

Farhan 2023-12-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2063817-backgroud-added-to-images-after-imwrap-transformations

评论： Farhan 2023-12-25

I am performing simple transformations but the Matlab adds backgroud to the image to make it Rectangle. The image has transparent backgroud. I know how to read the image and remove background but I fail to remove it after the transformations

I=imread('d.png');
I=flipud(I);
T = [1  0
     1 1]; 
figure;
T(3,3)=1;
[Iw,R]=imwarp(I, affine2d(T'));
h=imshow(Iw);
axis on xy;
set(h,'XData',R.XWorldLimits,'YData',R.YWorldLimits);
set(gca,'XLim',R.XWorldLimits,'YLim',R.YWorldLimits);

The following is being used

After the transformation the below image is displayed

I do not want this background to appear

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Answer 1

DGM 2023-12-25

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2063817-backgroud-added-to-images-after-imwrap-transformations#answer_1377152

在 MATLAB Online 中打开

Your image has alpha, but you're not using it.

% you need to read the whole image

[I,~,alpha] = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1575777/image.png');

% i don't know why you're flipping this,

% but the image will be upside-down when displayed (unless you display it upside-down)

% and it will be upside-down when you save it

I = flipud(I);

alpha = flipud(alpha);

% build T

T = [1 0; 1 1];

T(3,3) = 1;

% you could attach the alpha and transform this as a single RGBA array

% but imshow() and imwrite() won't know what to do with it.

[Iw,R] = imwarp(I, affine2d(T'));

[alphaw,~] = imwarp(alpha, affine2d(T'));

% display it

h = imshow(Iw);

h.AlphaData = alphaw; % this is the only way you can use alpha in imshow()

axis on xy; % you're displaying it upside-down

set(h,'XData',R.XWorldLimits,'YData',R.YWorldLimits);

set(gca,'XLim',R.XWorldLimits,'YLim',R.YWorldLimits);

% save it with alpha

imwrite(Iw,'out.png','alpha',alphaw)

As the comments state, you're creating an upside-down image, but you're also viewing it upside-down. I don't know what that means to you.

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Farhan 2023-12-25

I didn't understood teh code much, Thanks for such clear comments now I know much of the code. I just wanted to do transformation someone helped me wrote this code. I will change it as you suggested. Thanks

Farhan 2023-12-25