How to change the black color into transparency in png format?

colorImage = imread('13100.png');
grayImage = rgb2gray(colorImage);
mserRegions = detectMSERFeatures(grayImage);
mserRegionsPixels = vertcat(cell2mat(mserRegions.PixelList));

mserMask = false(size(grayImage));
ind = sub2ind(size(mserMask), mserRegionsPixels(:,2), mserRegionsPixels(:,1));
mserMask(ind) = true;
f=figure();imshow(mserMask,'Border','tight');

maskedimage = immultiply(colorImage, repmat(mserMask, [1, 1, size(colorImage, 3)]));
imshow(maskedimage,'Border','tight');

TransparencyMaskedImage = maskedimage;
TransparencyMaskedImage(repmat(~mserMask, 1, 1, 3)) = ??;
imshow(TransparencyMaskedImage,'Border','tight');

Answer 1

[Walter Roberson]

To just write it transparent with imwrite, you do not need any of the three lines

TransparencyMaskedImage = maskedimage;
TransparencyMaskedImage(repmat(~mserMask, 1, 1, 3)) = ??;
imshow(TransparencyMaskedImage,'Border','tight');

instead,

imwrite(maskedimage, 'YourFileName.png', 'Transparency', [0 0 0]);

If you want to display the image with transparency, then

   mask = double( any(maskedimage, 3) );
   image(maskedimage, 'AlphaData', mask )    %notice this is not imshow

[Mei Synn Tan]

Thanks for helping. Have a nice day

Answer 2

[Muhammad Zeeshan Ahmed Khan]

When you image() or imagesc() or imshow(), pass an option 'AlphaData' that is an array with the desired transparency, with 1 meaning to show the image completely and 0 meaning not showing the image at all (that is, show the background completely there.)

If the PNG had alpha information stored with it that you read with imread() then you should be able to use that transparency information directly.

[YourImage, ~, ImageAlpha] = imread('YourFile.png');

image(YourImage, 'AlphaData', ImageAlpha)

[Walter Roberson]

Copied without attribution from my answer to https://www.mathworks.com/matlabcentral/answers/365228-can-a-png-image-be-displayed-without-displaying-the-black-fill-in-the-guide#answer_289605