matlab 填充透明色,在Matlab中使用透明像素填充数组

我已经在matlab中编写了一段代码，将图像大小调整为特定大小(不会使它们变形)，并在必要时应用填充。

但是，填充是黑色的，我希望它是透明的。我不知道该怎么做。这是我有的代码：

% global variables

inputFolder = 'input/images/';

outputFolder = 'input/resized/';

extension = 'jpg';

x = 1000;

y = 1000;

% list all the files in the input folder

fileList = dir([inputFolder '*.' extension]);

% loop through all the files in the input folder, resize, pad and save

for i=1:length(fileList)

% get filename and load image

fname = fileList(i).name;

container = imread([inputFolder fname]);

% calculate local variables

containerY = size(container,1);

containerX = size(container,2);

containerProp = containerX / containerY;

canvasProp = x / y;

% determine proportions, apply padding and resize

if containerProp < canvasProp

container = imresize(container, [y NaN]);

containerX = size(container,2);

container = padarray(container, [0 floor((x - containerX)/2)], 0, 'pre');

containerX = size(container,2);

container = padarray(container, [0 (x - containerX)], 0, 'post');

elseif containerProp == canvasProp

container = imresize(container, [y x]);

else

container = imresize(container, [NaN x]);

containerY = size(container,1);

container = padarray(container, [floor((y - containerY)/2) 0], 0, 'pre');

containerY = size(container,1);

container = padarray(container, [(y - containerY) 0], 0, 'post');

end

% save resized image

imwrite(container, [outputFolder fname]);

end有谁知道如何将填充从黑色更改为透明？