How do I update an image object in App Designer?
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Gary Burton-Wilcock
le 28 Juin 2019
Commenté : RITAM BASU
le 29 Août 2022
I'm using the App Designers image object to display a jpeg. The code modifies the image data and then writes it back to the jpeg. However if I reload it in the image object it uses the original jpeg - presumably cached and not updated. The only way I have found to make it use the new image is to use a different filename for the modified image and then point to the new file. The image object appears to have a reset function but trying to use it causes a 'no method' error.
4 commentaires
Geoff Hayes
le 28 Juin 2019
Gary - so the only difference in the image is that you have added 25 to all elements of the app.img object? Do you see a change (in the image) when you view the updated image outside of MATLAB? Do you need to somehow refresh the app.Image?
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Guillaume
le 28 Juin 2019
Yes, I can observe the same behaviour. I've not been able to find exactly which class is responsible for the problem yet, it's not the Image class itself, the class mark itself as dirty every time you set the ImageSource property. It must be something else upstream that sees that the filename hasn't changed and hence do not update the display. I'll report the problem to matlab.
On the other hand, personally, I'd never give a filename to ImageSource, instead I'd passed an image array:
function readButtonPushed(app, event)
app.img = imread("lena512.bmp");
app.Image.ImageSource = repmat(app.img, 1, 1, 3); %ImageSource wants a RGB image, not a greyscale image
% the image appears in the Image control
end
% Button pushed function: modifyButton
function modifyButtonPushed(app, event)
app.img = app.img + 25;
end
% Button pushed function: reloadButton
function reloadButtonPushed(app, event)
app.Image.ImageSource = repmat(app.img, 1, 1, 3);
end
which doesn't have the same problem.
8 commentaires
Image Analyst
le 29 Août 2022
@RITAM BASU That's because it doesn't do anything. The output is the same as the input.
img = randi(255, 3, 3) % Create sample image.
img2 = repmat(img, 1, 1, 1) % Do RITAM's "solution"
RITAM BASU
le 29 Août 2022
Ah okay... It is exactly what I wanted. Just to open updated image every time. making it (1,1,3) gave me error mentioned by Bhisma Adhikari.
I did not fully comprehend the use of writing the 3 though. Is it to make a greyscale picture RGB ? I see that Making it 3 makes 3 copies of the same array(img2 here).
Thanks for the comment..
Have a nice day..
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