Control image transparency with a slider- appDesigner

Hi all,

I'm trying to control de tranparency of two images using a slider.

Currently, I don't know how to do the code for this feature with a callback function with the slider.

Can anybody help me?

What I wanted, for a better understanding, is that when I'm at a max value, I only see one of the images and at the min value I only see the other. Obviously, when I move the slider I want the transparency of them to change.

Thanks in advance

JM

[Adam]

If you keep hold of the image handles on your main app object then it is simply a case of updating the AlphaData properties of each of the images to whatever you want in your slider callback, based on the current value of the slider.

[João Mendes]

First of all, thanks.

I'm a truly begginer and I didn't fully understand your point.

Could you please explain that to me with some code examples?

Sorry and thanks

[Adam]

It would be easier if you post the relevant code you currently have. I don't really have time for long answers from scratch, hence me adding a comment rather than an 'Answer'

Answer 1

[Adam Danz]

This should get you started.

Two images are plotted on top of each other. A slider is added that sets the AlphaData of the top image.

% Create a figure with two images overlayed 
fig = uifigure('HandleVisibility','on'); 
[X,cmap] = imread('corn.tif');
imshow(X,cmap);
hold on
[X2,map] = imread('peppers.png');
img2 = imshow(X2,map);

% Create a GUI with a slider that controls the 'AlphaData' value of the currently selected object
sld = uislider(fig,'Position',[50,50,300,3],'Value',1,'Limits',[0,1],...
    'ValueChangingFcn', @(sld,event)changeTransparencyFcn(sld,event,img2),...
    'BusyAction', 'cancel');
% set the slider properties such as position etc....
% % https://www.mathworks.com/help/matlab/ref/uislider.html

function changeTransparencyFcn(~, event, hobj)
% hobj is the image object handle
set(hobj,'AlphaData', event.Value)
drawnow limitrate
end

Changes made to improve answer on Feb 9, 2021.

[João Mendes]

Wow. Thank you very much!

[Georg Edelmann]

Hey geat job!

I am trying to do a simialr Job in Matlab. I´d like to change the Sensetitivy of 'imbinarize' using a slider.

Here is my Code so far.

clf()
I= imread('Bild_1.jpg'); 
I=I(:,:,1);
I = imbinarize(I,'adaptive','ForegroundPolarity','dark');%,'Sensitivity',0.0);
imshow(I);

fig = uifigure();
fig.Position([3,4]) = [400,75];
sld = uislider(fig,'Position',[50,50,300,50],'Value',1,'Limits',[0,1],...
    'ValueChangedFcn', @(sld,event)changeSensitivityFcn(sld,event));


function changeSensitivityFcn(sld, event)
set(gco,'Sensitivity', sld.Value)
drawnow()
end

i hope you can help me

Thanks

[Adam Danz]

"Sensitivity" is not a property of images. The line set(gco, PROPERTY, VALUE) sets a property of the current object. See this page for a list of image properties.

[Georg Edelmann]

Hey thanks for your quick response!

How else could it be done?

function changeSensitivityFcn(sld, event)
Sensitivity=sld.Value
drawnow()
end

Using this code, i am able to change my Sensitivity Parameter as i can see in the Command Window, but the image itself does not change. Why?

Thanks

[Adam Danz]

In my answer,

set(gco,'AlphaData', sld.Value)

the slider is controlling the AlphaData property values of the currently selected image.

The link I provided in my previous comment lists properties of images. I don't know what you define as "sensitivity". If you can't figure that out, it might be better to post a new questions since I have limited time right now (feel free to link to this answer).