imwrite saving image incorrectly

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Harry West
Harry West on 8 Dec 2020
Commented: Ameer Hamza on 8 Dec 2020
I am trying to use app designer to create an app where you can load an image from your desktop, compress or decompress the image and then save the image. I have been able to load the image without any issues however when I save the image it removes the background or makes the whole image black. Heres my code:
[file, path] = uiputfile('.png');
image = imread(app.imagePath);
app.imagePath is the path to the original image that I want to save

Answers (1)

Ameer Hamza
Ameer Hamza on 8 Dec 2020
Does your png image have transparent components? Try saving with the alpha channel.
[file, path] = uiputfile('.png');
[image, ~, amap] = imread(app.imagePath);
imwrite(image,fullfile(path,file), 'Alpha', amap)
Ameer Hamza
Ameer Hamza on 8 Dec 2020
Ok, the issue is not the alpha map; rather, the png file is saved as an indexed image.
Either convert it to rgb image before using imwrite()
[img, cmap] = imread('block.png');
img_rgb = ind2rgb(img, cmap);
imwrite(img_rgb, 'test.png')
or specify colormap in imwrite()
[img, cmap] = imread('block.png');
imwrite(img, cmap, 'test.png')

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