How to plot png images with transparent background?

I've just used image(), and the transparent area are shown with black colour by default, however I need white background. I tried to use set(gcf,'color','white') but this cannot help.

Answer 1

[Walter Roberson]

When you image() pass in 'AlphaData', and the transparency data. The alpha needs to be floating point (not logical) in the range 0 to 1 and the same size as the image.

[Walter Roberson]

[img, map, alphachannel] = imread('YourImage.png');
image(img, 'AlphaData', alphachannel);

Answer 2

[Mr M.]

OK, but how to read the png to keep transparent background?

[Cris LaPierre]

Images get displayed in an axes. Even if the image doesn't have a background, it will at least originally display in an axes with a background color set to white. You can turn that off using

axis off

of

set(gca,'Color','none')

[DGM]

If you're trying to retain the original alpha content from the PNG file:

% read the image and its alpha
[inpict,~,alpha] = imread('peppers_rgba.png');

% show the image with the alpha from the file
image(inpict,'alphadata',im2double(alpha))

% set the axes background color if desired
set(gca,'color',[0.8 0.3 1])

If instead, your concern is how the transparent regions are visualized, then consider this example regarding display matting for transparent images.