MATLAB Central Newsreader - getimage (IPT) weirdness

getimage (IPT) weirdness

Eddie — Tue, 14 Oct 2008 18:21:02 -0400

So, my understanding of the documentation of the getimage function from the Image Processing Toolbox is that if I say:

xp = linspace(-10,10,350);
fig = figure;
plot(xp,xp.^2);
A = getimage(fig);

A should now be a matrix that contains the data relating to the pixels of the figure with the plotted parbola. However, when I try this, A is empty.

What I am doing wrong?

Re: getimage (IPT) weirdness

Walter Roberson — Tue, 14 Oct 2008 18:27:47 -0400

Eddie wrote:
> So, my understanding of the documentation of the getimage function from the Image Processing
> Toolbox is that if I say:

> xp = linspace(-10,10,350);
> fig = figure;
> plot(xp,xp.^2);
> A = getimage(fig);

> A should now be a matrix that contains the data relating to the pixels of the figure with
> the plotted parbola. However, when I try this, A is empty.
> What I am doing wrong?

Look at the documentation again. getimage() returns whatever is in the first CData array
that is found under the given handle. Objects of type image have CData arrays (as well as
some other kinds of objects such as objects of type patch), but plot() creates
objects of time axes and lineseries, neither of which have CData arrays.

Perhaps what you wanted to look at was getframe().

Re: getimage (IPT) weirdness

Eddie — Tue, 14 Oct 2008 18:52:01 -0400

Walter Roberson <roberson@hushmail.com> wrote in message <ew5Jk.11$tV.9@newsfe08.iad>...
> Eddie wrote:
> > So, my understanding of the documentation of the getimage function from the Image Processing
> > Toolbox is that if I say:
>
> > xp = linspace(-10,10,350);
> > fig = figure;
> > plot(xp,xp.^2);
> > A = getimage(fig);
>
> > A should now be a matrix that contains the data relating to the pixels of the figure with
> > the plotted parbola. However, when I try this, A is empty.
> > What I am doing wrong?
>
> Look at the documentation again. getimage() returns whatever is in the first CData array
> that is found under the given handle. Objects of type image have CData arrays (as well as
> some other kinds of objects such as objects of type patch), but plot() creates
> objects of time axes and lineseries, neither of which have CData arrays.
>
> Perhaps what you wanted to look at was getframe().

OK, you're right. I saw that a figure was a valid argument to the function, and assumed magic would happen. getframe() won't work for my purposes though because I need to suppress the actual display of the plot, and getframe() requires the figure to be visible. Other suggestions?