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