Alpha transparency on PNGs in IE 1

[BillyRayPreachersSon]

Just a quick heads-up to anyone using the AlphaImageLoader filter in IE to get PNG transparency working in IE (I spent many hours at the weekend trying to find out why it wasn't working for me):

The PNG files need to be 32-bit.

Hope this helps,
Dan



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[tsdragon]

Thanks Dan, that's good to know!

Tracy Dryden

Meddle not in the affairs of dragons,
For you are crunchy, and good with mustard.

 

[Foamcow]

32 rather than 24 bit?

I thought pngs were either 8 or 24 bit.

IE supports 8 bit doesn't it? 24 bits give you the nice smooth alpha channel that IE likes to colour blue

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Foamcow Heavy Industries - Web site design in Cheltenham and Gloucester
Earl & Thompson Marketing - Marketing Agency Services in Gloucestershire

 

[BillyRayPreachersSon]

I did a test at the weekend... 8-bits gave transparency only where the alpha was 100%, 24-bit gave no transparency at all (in either IE or Firefox, would you believe), and 32-bit gave perfect results in both (with the Alpha filter in IE)... so I guess they do have to be 32-bit.

Fireworks certainly let you export as 32-bit so maybe your graphics package is one option missing?

Dan

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[Foamcow]

Hmmm, Photoshop is normally pretty thorough

PNG8 files should work in IE but because there are only 256 "tones" in the transparency channel the transparency effect is often disappointing.

PNG24 format (I assume it's 24 bit by the name) have much smoother transparency due to the increased number of steps. It is also possible to create percentage opacity with them.

IE only supports 8 bit PNG files - it renders the 24 bit transparency channel as a blue(ish) mask.

Firefox (and others) support 24 bit PNG's perfectly. I just tested it and it works

Have a look

http://www.foamcow.com/tests/pngtrans/

I'd be interested to know what it is you are doing that isn't working. Perhaps it's something to do with the AlphaImageLoader you mentioned. But FF should support 24bit PNG transparency out of the box.


Ahaaa.... Read this

http://www.libpng.org/pub/png/pngfaq.html#png8-png24

It seems that there are 2 formats, 8 and 24 bit. But with the alpha channel, 24 bit becomes effectively 32 bit.
So a 32 bit PNG is a 24 bit one with an alpha channel!

Glad we cleared that up lol

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Foamcow Heavy Industries - Web site design in Cheltenham and Gloucester
Earl & Thompson Marketing - Marketing Agency Services in Gloucestershire