MATLAB Central Newsreader - How to show figure without black portion?

How to show figure without black portion?

Nan W. — Sat, 19 Jul 2008 02:53:02 -0400

Dear all,

I would like to know whether there is any techniques to show
to image in MATLAB without black portion border? My case is
I tried to superimpose two images with one is the rotate
version of another. So it would be great if the final image
has no black area causing by 'imrotate'.

Thanks in advance.

Re: How to show figure without black portion?

Bruno Luong — Sat, 19 Jul 2008 06:09:01 -0400

"Nan W." <iiuu_chan@yahoo.co.jp> wrote in message
<g5rkue$4bg$1@fred.mathworks.com>...
> Dear all,
>
> I would like to know whether there is any techniques to show
> to image in MATLAB without black portion border? My case is
> I tried to superimpose two images with one is the rotate
> version of another. So it would be great if the final image
> has no black area causing by 'imrotate'.
>
> Thanks in advance.

Have you tried 'crop' option in the 4th argument of imrotate?

If it's not enough you might calculate the thickness of the
border from image size and rotation angle and throw manually
the borders.

I believe cropping will keep the same image size/image
magnification, but with a small border. Remove completely
the borders would change the original magnification, aspect
ratio, and image size.

Bruno

Re: How to show figure without black portion?

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) — Mon, 21 Jul 2008 21:10:56 -0400

In article <g5rkue$4bg$1@fred.mathworks.com>,
Nan W. <iiuu_chan@yahoo.co.jp> wrote:

>I would like to know whether there is any techniques to show
>to image in MATLAB without black portion border?

texture-map the image onto a patch object whose coordinates
are the rotated rectangular pixel coordinates.

>My case is
>I tried to superimpose two images with one is the rotate
>version of another. So it would be great if the final image
>has no black area causing by 'imrotate'.

You could convert your image to truecolor and use tformarray()
but that might be overkill.

You might be able to get somewhere by converting your image to
truecolor, padding it with NaN all around, rotating it, and then
setting any 0 that is before the first NaN or after the last NaN to
be whatever value you wanted (and the NaN too of course.)

The work becomes a -lot- easier if you know that the original
image has no 0's: then you just set all of the 0's of the
rotated image to be the value you want.

But if you are superimposing two images, then that suggests to me
that you might be interested in transparency; you can either do
the alpha calculations yourself or you can use patches anyhow.
--
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