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Re: overlaying a transparent 24-bit image with different pixel scale [message #73229 is a reply to message #73228]

Fri, 29 October 2010 11:44

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On Oct 29, 2:36 pm, David Fanning <n...@dfanning.com> wrote:
> Jeremy Bailin writes:
>> I can calculate the appropriate normalized coordinates corresponding
>> to the corners of where the image should be placed. I've tried feeding
>> that and the 24-bit image into TVIMAGE, but it uses a white background
>> for the alpha channel, not what already exists on the display. And
>> David's example for overlaying things (http://www.dfanning.com/ip_tips/
>> transparentpng.html) assumes a relative pixel scale of 1.
>
> Well, a new keyword will probably fix that up! :-)
>
> I was going to make a change to TVImage today anyway,
> so I might as well do this at the same time. My only
> concern is that if I take what's in the display window
> as the background for the alpha channel, this will NOT
> make it possible to display the image in PostScript.
> (No window to read from.) Is this a limitation you
> can live with?
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")

Unfortunately, that's kind of essential. :-( So I think rolling my
own is going to be necessary anyway... though it would certainly be a
good thing to have in TVIMAGE, even I can't use it today!

Since the background is something that I generate myself, I can fake
the output of TVRD by putting the 8-bit image through the colour
table. I should be okay as long as I can keep track of all the
different coordinates in several different coordinate systems on a
Friday afternoon. ;-)

-Jeremy.

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[Message index]

		Re: overlaying a transparent 24-bit image with different pixel scale By: David Fanning on Fri, 29 October 2010 13:35
		Re: overlaying a transparent 24-bit image with different pixel scale By: Jeremy Bailin on Fri, 29 October 2010 13:13
		Re: overlaying a transparent 24-bit image with different pixel scale By: David Fanning on Fri, 29 October 2010 12:24
		Re: overlaying a transparent 24-bit image with different pixel scale By: Jeremy Bailin on Fri, 29 October 2010 11:47
		Re: overlaying a transparent 24-bit image with different pixel scale By: Jeremy Bailin on Fri, 29 October 2010 11:44
		Re: overlaying a transparent 24-bit image with different pixel scale By: David Fanning on Fri, 29 October 2010 11:41
		Re: overlaying a transparent 24-bit image with different pixel scale By: David Fanning on Fri, 29 October 2010 11:36

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