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Re: Creating Transparent PNG Images [message #68443 is a reply to message #68442]

Sat, 24 October 2009 07:59

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Devin White writes:

> You can write out transparent 24-bit PNGs by supplying a 4-channel
> array to WRITE_PNG (4 x samples x lines). The first three channels
> are RGB, the fourth is the alpha channel. Fully visible pixels should
> have their corresponding alpha channel elements set to 255,
> transparent pixels should have theirs set to 0.

OK, well, then the documentation REALLY needs to be improved!

But there is still a problem. Consider the transparent PNG
image you find here:

http://www.dfanning.com/ip_tips/example.png

I tried this:

IDL> image = read_png('example.png')
IDL> help, image
IMAGE BYTE = Array[4, 162, 150]
IDL> write_png, 'test.png', image

Then, I opened both example.png and test.png in my
browser (FireFox). They appear to be two different
images! The test.png file appears in MUCH darker colors.

Any ideas on what this could be about?

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.")

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[Message index]

		Re: Creating Transparent PNG Images By: David Fanning on Sun, 25 October 2009 09:32
		Re: Creating Transparent PNG Images By: greg.addr on Sat, 24 October 2009 10:13
		Re: Creating Transparent PNG Images By: David Fanning on Sat, 24 October 2009 09:01
		Re: Creating Transparent PNG Images By: David Fanning on Sat, 24 October 2009 07:59
		Re: Creating Transparent PNG Images By: devin.white on Sat, 24 October 2009 05:33
		Re: Creating Transparent PNG Images By: Vince Hradil on Fri, 23 October 2009 13:05
		Re: Creating Transparent PNG Images By: David Fanning on Fri, 23 October 2009 12:18

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