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Re: transparent background [message #35364 is a reply to message #35296]

Thu, 05 June 2003 12:16

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Rick Towler (rtowler@u.washington.edu) writes:

> You didn't really fool around for 20 minutes, did you?

Indeed I did. I thought it might take five. And now
I've just spent another 15. :-)

> With the B/W linear color table loaded:
>
> IDL> test = BYTARR(200,200)
> IDL> test[100:199,*] = 200
> IDL> tvlct, r,g,b,/get
> IDL> write_png,'test.png',test,r,g,b,TRANSPARENT=[0]
>
>
> In PP, Insert -> Picture -> From File... and select 'test.png'
>
> I have a 200x200 image, right half is lt. gray, left half is transparent.
>
> Load test.png up in Photoshop and the left half of the image is transparent
> too.

Well, I can see this works. But why doesn't my test
program work?

PRO TEST
thisDev = !D.Name
white = FSC_Color('white', !D.Table_Size-2, Decomposed=0)
red = FSC_Color('red', !D.Table_Size-3, Decomposed=0)
green = FSC_Color('green', !D.Table_Size-4, Decomposed=0)
Set_Plot, 'Z', /Copy
Erase
Plot, findgen(11), Color=red, Background=white, /NoData
Oplot, findgen(11), Color=green
snapshot = TVRD()
tvlct, r,g,b,/get
Set_Plot, thisDev
write_png,'tester.png',snapshot,r,g,b,TRANSPARENT=[!D.Table_ Size-2]
Print, !D.Table_Size-2
I = Where(snapshot EQ !D.Table_Size-2, count) & Print, count
END

My background (index 254) is white. I want that to be the transparent
pixel value. There are 304,055 pixels in my image with this value.
You'd think a *few* of them would be transparent. But no, when
I put this into Powerpoint, I get an image with a white background.

Any ideas?

Cheers,

David
--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		transparent background By: craigni on Tue, 03 June 2003 09:59
		Re: transparent background By: Rick Towler on Thu, 05 June 2003 13:22
		Re: transparent background By: David Fanning on Thu, 05 June 2003 13:03
		Re: transparent background By: R.Bauer on Thu, 05 June 2003 12:43
		Re: transparent background By: David Fanning on Thu, 05 June 2003 12:16

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