How to preserve edges when rotating images

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Elysi Cochin
Elysi Cochin 2021-1-7
评论： Walter Roberson 2022-4-12
How can i make sure that my images dont cut off when using rotation in image augmentation
imageAugmenter = imageDataAugmenter('RandRotation',[0,360]);
In = imread('input_image.bmp');
Out = augment(imageAugmenter,In);
What additional parameters, do i need to set, to ensure the image dont get cut off at the edges

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Walter Roberson
Walter Roberson 2021-1-7
pad the image with nan so that it becomes sqrt(2) times its original size. Do the random rotation on that. Find the bounding box of non-nan elements and crop. Fill the remaining nan with something appropriate.
Or... don't use the image augmenter, and use imrotate with a random angle, specifying an appropriate padding strategy.
  2 个评论
Wan Faiz
Wan Faiz 2022-4-11
I cant find any examples on this. Can you explain how to implement it on the codes?
Walter Roberson
Walter Roberson 2022-4-12
Ran in:
sqrt(2) does not seem to quite do the trick, but slightly larger seems to work.
The display with alpha masking shows visually that you could then proceed to trim the leading and trailing all-nan rows and columns.
imageAugmenter = imageDataAugmenter('RandRotation',[0,360], 'FillValue', nan);
In = imread('flamingos.jpg');
Indouble = im2double(In);
nrow = size(Indouble, 1);
ncol = size(Indouble, 2);
factor = .4; %(sqrt(2) - 1)/2;
Indouble = padarray(Indouble, ceil([nrow ncol 0]*factor), nan);
Outdouble = augment(imageAugmenter, Indouble);
Out8 = im2uint8(Outdouble);
mask = isnan(Outdouble);
Out8(mask) = 0;
alphadata = double(~any(mask,3));
figure
h1 = imshow(Out8);
title('no alpha');
figure
h2 = imshow(Out8);
h2.AlphaData = alphadata;
title('alpha mask')
nnmask = all(~mask,3);
hmask = any(nnmask,1);
firstcol = find(hmask, 1);
lastcol = find(hmask, 1, 'last');
vmask = any(nnmask,2);
firstrow = find(vmask, 1);
lastrow = find(vmask, 1, 'last');
trimmed = Outdouble(firstrow:lastrow, firstcol:lastcol, :);
trimmed8 = im2uint8(trimmed);
mask8 = any(isnan(trimmed),3);;
trimmed8( repmat(mask8, 1, 1, 3)) = 0;
alphadata = double(~mask8);
figure
h3 = imshow(trimmed8);
h3.AlphaData = alphadata;
title('alpha mask after trim')

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