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Transparent PNG file on background in Matlab GUI

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Frank
Frank il 5 Giu 2012
Commentato: Serge il 6 Nov 2022
Hello,
For my GUI i have set a background image and now I want to put a (partly) transparent PNG image on a pushbutton on top of this background image, while keeping the background visible in the parts where the button image is transparent. How do I do this?
Thanks in advance!

Risposte (3)

Robert Cumming
Robert Cumming il 12 Dic 2014
I know this is an old post - but if anyone comes across this you may be interested in this blog on undocumentedmatlab

Klont
Klont il 26 Lug 2015
Modificato: Klont il 26 Lug 2015
Simply make a matrix of size height (pixels) x width (pixels) x 3 (rgb) of doubles between 0 and 1, with NaN indicating transparency.

Walter Roberson
Walter Roberson il 5 Giu 2012
You cannot do this directly. The uicontrol() that can have images placed on them (such as pushbutton) have a CData property that must be truecolor (RGB) values, but there is no alpha property, so there is no way to define transparency for such images.
The work-around is to figure out which part of the background image the button would be covering up, and to store the corresponding pixel values into the image array locations that should be transparent, and then to use that as the CData.
Ideally you would re-do this when the figure was resized; that would have to be triggered off of the figure resize callback, as uicontrol do not have a resize callback.
  2 Commenti
Frank
Frank il 6 Giu 2012
Thanks for the tip!
I tried the following code:
bg_image=imread('bg.png'); %background
pos_button=[500,500];
[button,button_map]=imread('button.png.'); %button image
[w,l,d]=size(button);
bg_button=bg_image(500:500+w,500:500+l); % part of background that is behind button
button = uicontrol('style','pushbutton','position',[pos_button,[w,l]]);
button_image=button;
for i=1:w
for j=1:l
for k=1:d
if button_image(i,j,k)==255 % places where background should be seen
button_image(i,j,k)=bg_button(i,j,k); %replace with background values
end
end
end
end
button_image_RGB=ind2RGB(button_image,button_off_map);
set(button,'cdata',button_image_RGB);
This works, but the colors of the background are not the colors they should be, but grey.
Any ideas why?
Walter Roberson
Walter Roberson il 6 Giu 2012
I suspect bg_image is 3 dimensional (truecolor, RGB) rather than 2 dimensional. You probably need to add a third index when extracting bg_button

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