Re: imread (repost)

[Daniel J Sebald]

Thomas Weber wrote:
> Am Dienstag, den 05.08.2008, 12:43 -0500 schrieb Daniel J Sebald:
>
> > Bill Denney wrote:
> >
> > > I would expect to see the axis background color.  If the axis background 
> > > color is set to none, then I would expect to see the figure background 
> > > color.  I believe that if you set the figure background color to none in 
> > > matlab, you see a cross-hatched pattern.  When exporting, I would 
> > > anticipate that the graphics backend would take alpha into account 
> > > relative to the output device, so if the output was to ps or pdf, it 
> > > would convert the background color to the color as visible on the screen.
> > >
> > > I'm not saying that this is easy, just that-- to me-- the above is the 
> > > right way to do it.
> >
> > In my opinion, the right way is for PostScript to handle alpha
> > blending.  Wish it would.  It's the easiest place to implement such a
> > feature, i.e., at the last step just blend the contents together.
>
>
> I'm not sure I understand, but Postscript seems to support an alpha
> channel:
> http://tug.org/PSTricks/main.cgi?file=Examples/Colors/colors#transparency
>
> The code example needs a development version of pstricks.
>
> The main problem is that most postscript _viewers_ don't handle
> transparency, so one usually converts to PDF.

I'm not so sure this is what we want.  This pstricks implementation is 
interesting.  There is the cross hatch fill that yields a good simulation of 
transparency.  It isn't really blending.  The other examples with opacity are 
sort of the right idea, but it isn't for an image, just fill shapes.  I see no 
example with an image having an arbitrary fourth channel.  (I suspsect that is 
because PostScript and PDF don't support that.)

Dan