Thread Subject:

Interesting problem with image alpha data

 I have come across an interesting problem with setting the alpha data for an image, which I can't quite get my head around.

 To explain, consider the following example:

 h1 = figure(1);
 h1a = axes('DataAspectRatio', [1 1 1], 'DrawMode', 'fast', 'Parent', h1);
 h1b = image('Parent', h1a);

 All works as expect, then:

 set(h1b, 'CData', imread('Peppers.png')); % load a test image.

 This works just as would be expected. So, I then try:

 set(h1b, 'AlphaData', 0.75);

 Which has the right effect. However, this image isn't positioned very nicely within the axes, so I use:

 set(h1a, 'XLim', [1 512], 'YLim', [1 384], 'YDir', 'reverse');

 Which makes everything look nice. But now if I set the alpha data to anything other than 1, the image just dissappears completely. Can anyone tell me what is going wrong here?

 I'm using Matlab R2009a with version 6.3 of the Image Processing toolbox.

 Many thanks!

"Michael " <michael.bennett@lineone.net> wrote in message <h1fj4i$7ln$1@fred.mathworks.com>...
> I have come across an interesting problem with setting the alpha data for an image, which I can't quite get my head around.
>
> To explain, consider the following example:
>
> h1 = figure(1);
> h1a = axes('DataAspectRatio', [1 1 1], 'DrawMode', 'fast', 'Parent', h1);
> h1b = image('Parent', h1a);
>
> All works as expect, then:
>
> set(h1b, 'CData', imread('Peppers.png')); % load a test image.
>
> This works just as would be expected. So, I then try:
>
> set(h1b, 'AlphaData', 0.75);
>
> Which has the right effect. However, this image isn't positioned very nicely within the axes, so I use:
>
> set(h1a, 'XLim', [1 512], 'YLim', [1 384], 'YDir', 'reverse');
>
> Which makes everything look nice. But now if I set the alpha data to anything other than 1, the image just dissappears completely. Can anyone tell me what is going wrong here?
>
> I'm using Matlab R2009a with version 6.3 of the Image Processing toolbox.
>
> Many thanks!

Has anyone else seen this problem? More importantly, has anyone identified a viable solution?

In article <h99et9$5as$1@fred.mathworks.com>,
whichpart.wwinter.isnotanemail@uci.edu says...
> "Michael " <michael.bennett@lineone.net> wrote in message <h1fj4i$7ln$1@fred.mathworks.com>...
> > I have come across an interesting problem with setting the alpha data for an image, which I can't quite get my head around.
> >
> > To explain, consider the following example:
> >
> > h1 = figure(1);
> > h1a = axes('DataAspectRatio', [1 1 1], 'DrawMode', 'fast', 'Parent', h1);
> > h1b = image('Parent', h1a);
> >
> > All works as expect, then:
> >
> > set(h1b, 'CData', imread('Peppers.png')); % load a test image.
> >
> > This works just as would be expected. So, I then try:
> >
> > set(h1b, 'AlphaData', 0.75);
> >
> > Which has the right effect. However, this image isn't positioned very nicely within the axes, so I use:
> >
> > set(h1a, 'XLim', [1 512], 'YLim', [1 384], 'YDir', 'reverse');
> >
> > Which makes everything look nice. But now if I set the alpha data to anything other than 1, the image just dissappears completely. Can anyone tell me what is going wrong here?
> >
> > I'm using Matlab R2009a with version 6.3 of the Image Processing toolbox.
> >
> > Many thanks!
>
> Has anyone else seen this problem? More importantly, has anyone identified a viable solution?
>

It works for me in both R2009a and R2009b.

--
Loren
http://blogs.mathworks.com/loren

"Michael " <michael.bennett@lineone.net> wrote in message <h1fj4i$7ln$1@fred.mathworks.com>...
> I have come across an interesting problem with setting the alpha data for an image, which I can't quite get my head around.
>
> To explain, consider the following example:
>
> h1 = figure(1);
> h1a = axes('DataAspectRatio', [1 1 1], 'DrawMode', 'fast', 'Parent', h1);
> h1b = image('Parent', h1a);
>
> All works as expect, then:
>
> set(h1b, 'CData', imread('Peppers.png')); % load a test image.
>
> This works just as would be expected. So, I then try:
>
> set(h1b, 'AlphaData', 0.75);
>
> Which has the right effect. However, this image isn't positioned very nicely within the axes, so I use:
>
> set(h1a, 'XLim', [1 512], 'YLim', [1 384], 'YDir', 'reverse');
>
> Which makes everything look nice. But now if I set the alpha data to anything other than 1, the image just dissappears completely. Can anyone tell me what is going wrong here?
>
> I'm using Matlab R2009a with version 6.3 of the Image Processing toolbox.
>
> Many thanks!

I had a very similar problem and it turned out to be a bug with OpenGL. I tried it on another computer and it just worked! Right now I am trying to update my OpenGL driver.

Worked out for me:
rotate the picture a little bit...


"Michael " <michael.bennett@lineone.net> wrote in message <h1fj4i$7ln$1@fred.mathworks.com>...
> I have come across an interesting problem with setting the alpha data for an image, which I can't quite get my head around.
>
> To explain, consider the following example:
>
> h1 = figure(1);
> h1a = axes('DataAspectRatio', [1 1 1], 'DrawMode', 'fast', 'Parent', h1);
> h1b = image('Parent', h1a);
>
> All works as expect, then:
>
> set(h1b, 'CData', imread('Peppers.png')); % load a test image.
>
> This works just as would be expected. So, I then try:
>
> set(h1b, 'AlphaData', 0.75);
>
> Which has the right effect. However, this image isn't positioned very nicely within the axes, so I use:
>
> set(h1a, 'XLim', [1 512], 'YLim', [1 384], 'YDir', 'reverse');
>
> Which makes everything look nice. But now if I set the alpha data to anything other than 1, the image just dissappears completely. Can anyone tell me what is going wrong here?
>
> I'm using Matlab R2009a with version 6.3 of the Image Processing toolbox.
>
> Many thanks!