imcrop can not work for a .fig file

When I use this function,

I = openfig('filename.fig');
J = imcrop(I,rect)

output:

Error using imcrop>checkCData (line 412)

Invalid input image.

Error in imcrop>parseInputs (line 256)

checkCData(a);

Error in imcrop (line 93)

[x,y,a,cm,spatial_rect,h_image,placement_cancelled] = parseInputs(varargin{:});

But when use another (below), it works.

[J,rect2] = imcrop(___)

Can another people help? thanks.

[Adam]

doc openfig

returns a figure object, i.e. the window containing the axes. You need actual image data. With numerous assumptions on what is actually in the figure you can get this data as e.g.

hFig = openfig( ... );
hAxes = hFig.CurrentAxes;
hImage = hAxes.Children;
I = hImage.CData;

It's a very brittle way to achieve this though. image data should be stored in image files or in .mat files that you can load the actual data in from and use that directly rather than having to fish the data out of a figure.

The above assumes you have 1 axes in the figure and that the only thing in that axes is the image which you want.

[Winston]

>> hFig = openfig('defocus6_-51.04.fig');
hAxes = hFig.axes.CurrentAxes;
hImage = hAxes.Children;
output
Unrecognized method, property, or field 'axes' for class 'matlab.ui.Figure'.

[Walter Roberson]

I notice that you have a matlab.ui.Figure, also known as a uifigure, which is produced by App Designer. I did not know that you could get a .fig from App Designer. Using CurrentAxes and so on is for old style figures. I do not have any uifigure around to test with.

[Adam]

Sorry, corrected that now. I thought the property was 'Axes' first, then double-checked, found it was 'CurrentAxes' and didn't realise I hadn't removed the first attempt!

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/images/ref/imhandles.html can be used to locate the images in fig. Note that more than one could potentially be returned in general.

[Winston]

this function seems not working

h = openfig('defocus6_-51.04.fig');
I = imhandles(gca)
J = imcrop(I, [372, 177, 346, 273]);

[Walter Roberson]

h = openfig('defocus6_-51.04.fig');
I = imhandles(h);
numimg = length(I);
if numimg == 0
    error('figure does not have any images.')
end
J = cell(numimg);
for K = 1 : numimg
  J{K} = imcrop(I(K), [372, 177, 346, 273]);
end
fprintf('%d images cropped into J\n', numimg);

[Winston]

sorry, I realize

it says 'Undefined function or variable 'numing''.

[Walter Roberson]

Sorry, I fixed the typing mistake.

[Winston]

Thanks, but seems more errors

Error using imcrop>checkCData (line 412)

Invalid input image.

Error in imcrop>parseInputs (line 256)

checkCData(a);

Error in imcrop (line 93)

[x,y,a,cm,spatial_rect,h_image,placement_cancelled] = parseInputs(varargin{:});

codes:

h = openfig('defocus1_-76.04.fig');
I = imhandles(h);
numimg=length(I);
if numimg == 0
    error('figure does not have any images.')
end
J = cell(numimg);
for K = 1 : numimg
  J{K} = imcrop(I(K), [44, 166, 50, 50]);
end
fprintf('%d images cropped into J\n', numimg);

[Walter Roberson]

h = openfig('defocus1_-76.04.fig');
I = imhandles(h);
numimg = length(I);
if numimg == 0
    error('figure does not have any images.')
end
J = cell(numimg, 1);
for K = 1 : numimg
  J{K} = imcrop(I(K).CData, [44, 166, 50, 50]);
end
fprintf('%d images cropped into J\n', numimg);

This might not be exactly what you want. You are on the border between asking for an interactive cropping tool, or automatically cropping at a fixed location, but you cannot do both at the same time: you can only specify a crop rectangle when you do not use an interactive cropping tool. The code I show here guesses that you wanted to crop a particular rectangle instead of invoking the interactive cropping tool.

[Winston]

Hi Walter,

no matter either interactive or specifying a crop rectangle, will they always use imcrop() funcition? why it works well for .tif or jpeg, but not on .fig?

I also tried to export .fig to .tif but this will change the pixel number in the .fig.

I have tried your codes and it does work to give a 1*1 cell array, but this array can not give the image, when I imshow([J{:}]), do you have any idea?

[Walter Roberson]

.fig are not image files, they are complicated data structures. A .fig is effectively an entire figure window, not a particular image within the figure. You cannot crop an entire figure.

What shows up for

min(J{1}(:))
max(J{1}(:))
class(J{1})
size(J{1})

[Winston]

They are

ans =

7618074

ans =

9306097

ans =

'double'

ans =

51 51

J{K} = imcrop(I(K).CData, [44, 166, 50, 50]); is used, no idea about why the cropped gives 51*51

[Walter Roberson]

imshow(J{1} ,[])

imcrop includes the border, except when it does not include the border. I filed a bug report on it years ago.

I recommend using matrix indexing instead of imcrop when you already know where you want to crop.