Why does IMWRITE produce an empty image when I try to save a figure to the disk folder?

I currently have a MATLAB figure that has a button to allow the user to save that image to the folder. I would like when the user clicks on the button, the save dialog window to appear so that the user can specify the name, type and location.

From the search that I did in here, I think I need to use uiputfile and imwrite to accomplish this. I tried the code below which is called when the user click on the save button but it saves an empty image. fh3 is the handle for the figure.

function pbsave_callback(source, eventdata, fh3)

[files, path, index] = uiputfile({'*.jpg';'*.gif';'*.*'},'Save As');

imwrite(fh3, files, 'jpg');

end

Answer 1

[Jan]

IMWRITE needs an array containing the captured pixels as input, not the figure handle:

function pbsave_callback(source, eventdata, fh3)
[FileName, FilePath] = uiputfile({'*.jpg';'*.gif';'*.*'},'Save As');
File = fullfile(FilePath, FileName);

Img = getframe(fh3);
imwrite(Img.cdata, File, 'jpg');

I've used FULLFILE to consider the chosen folder.

EDITED: "FileName" -> "File", 1 output for GETFRAME - omit support of Matlab 5.3

[S]

Thanks Jan, the code saves the image perfectly with everything in place. I am just wondering what is the use of File as you are not using it in the code. Also why are you checking for Map if empty or not?

[Jan]

@S: I've fixed the FileName typo. Using GETFRAME with 2 outputs and catching an empty Map supports indexed colors of Matlab R11. I'll remove this immediately and hope, that this does not affect too many readers...

Answer 2

[Walter Roberson]

imwrite() writes a matrix of data as an image. It is taking your fh3 as a single 1 x 1 pixel of image data.

Use saveas() to copy figures to image files.

Answer 3

[S]

Thanks Walter, I tried saveas() and it worked but it messed up my uicontrols on the figure (I had a button and dropdown at the top but the saved image shows them almost in the middle). Is there anyway I can have the saved image appear the same as it was before on the screen?

[Walter Roberson]

What Units are you using for the controls?

When you saveas() or print() the figure PaperPosition and PaperPositionMode take effect, with an effective resize operation.

I recommend you use the matlab file exchange contribution "export_fig"

[S]

Im using the default units ( should be pixels). It could be true however with imwrite suggested by Jan's, it kept the positions of all the uicontrols in place. Thank you very much for you suggestions.