Saving as transparent png-24 in 7.0??

S
Posted By
skhan
May 2, 2004
Views
401
Replies
9
Status
Closed
Does anyone know how to save images as png-24 without a light blue background appearing in the transparent area when applying the image to a web-page??
Related Tags
png save transparency

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MM
Mac_McDougald
May 2, 2004
It’s just browser dependent.
I get gray (not blue) if viewed in IE6.
However, Mozilla works fine, transparent as desired.

That’s why I see PNG still as non-viable, unless MS supports it. And even if they do in future version, you’ve still got all the legacy browser versions that don’t.

Mac
TM
Trevor_Morris
May 2, 2004
Well, you can actually achieve dual-browser (i.e., I.E. and every other browser 😉 ) PNG alpha transparency using IE’s AlphaImageLoader tag. Complete description and examples provided here:

Cross-Browser Variable Opacity with PNG: A Real Solution <http://www.alistapart.com/articles/pngopacity/> (www.alistapart.com)

Admittedly it is a pain that Microsoft does not just support PNG alpha transparency directly, but at least there is a relatively simple workaround.
MM
Mac_McDougald
May 2, 2004
Whew…at least it’s simple 😐

Mac
A
Alexander
May 3, 2004
Thanks for that link, Trevor! 😀
A neat and quick workaround…

Al
TM
Trevor_Morris
May 4, 2004
I too thought it appeared complicated at first, but it really is quite simple. For IE only, just use the AlphaImageLoader filter. For all other browsers, just call the image in a regular img tag. For both browsers, use the supplied browser detect script from the link above.

To demonstrate all of this, I threw together the following page which shows how RGBA and alpha-indexed PNGs behave using traditional img, AlphaImageLoader and a combination of both (i.e., browser detection).

Alpha PNG Test Page <http://user.fundy.net/morris/pngtest/pngtest.html>

Help yourself to any of the code, etc.
TM
Trevor_Morris
May 5, 2004
BTW, I should mention that the alpha-indexed PNGs (in the above link) were converted from 8-bpc RGBA PNGs using PNGQuant, since Photoshop itself is not capable of saving out alpha-indexed PNGs.
TZ
testosterone_z
May 22, 2004
BTW, I should mention that the alpha-indexed PNGs (in the above link)
were converted from 8-bpc RGBA PNGs using PNGQuant, since Photoshop >itself
is not capable of saving out alpha-indexed PNGs.

At least since Version 6. Photoshop 5 on the Mac does save PNGs (indexed or full color) with an alpha channel. Although it saves PNGs with a gamma value that’s way off.

Why newer versions of Photoshop don’t respect it’s own alpha channel is a total mystery to me.
CC
Chris_Cox
May 24, 2004
Because the PNG spec says it uses transparency, not arbitrary alpha.
TM
Trevor_Morris
May 25, 2004
Agreed (with Chris), I much prefer the current method. Whatever appears as transparent remains transparent–intuitive and consistent with the way other formats work.

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