Transparent PNGs and Netscape 4.7

[pduggan]

Not sure if this is the best place for this (might have been better under 'Site Design and Publishing'), but I didn't want it to get buried in my earlier thread...

Guess most of you graphics experts might know this anyway, but Netscape 4.7 doesn't display transparent PNGs properly. No problems with normal PNGs or any type of GIFs, but transparent PNGs appear backed by a white rectangle to the full image size (disastrous if they've been anti-aliased to a different colour!).

All fine in Internet Explorer 5.5, Opera 5 and Netscape 6...

Have to say that I hate Netscape 4.7 (and probably every other version of Netscape 4?) because it contrives to make a mess of almost everything, but lots of folk still use it and I keep a copy just to see how bad my site could look if I'm not careful.

As for why I've been using PNGs in preference to GIFs in the first place, that's another story altogether!

Peter

[pduggan]

Not sure if this is the best place for this (might have been better under 'Site Design and Publishing'), but I didn't want it to get buried in my earlier thread...

Guess most of you graphics experts might know this anyway, but Netscape 4.7 doesn't display transparent PNGs properly. No problems with normal PNGs or any type of GIFs, but transparent PNGs appear backed by a white rectangle to the full image size (disastrous if they've been anti-aliased to a different colour!).

All fine in Internet Explorer 5.5, Opera 5 and Netscape 6...

Have to say that I hate Netscape 4.7 (and probably every other version of Netscape 4?) because it contrives to make a mess of almost everything, but lots of folk still use it and I keep a copy just to see how bad my site could look if I'm not careful.

As for why I've been using PNGs in preference to GIFs in the first place, that's another story altogether!

Peter

[pduggan]

Sorry I'm replying to my own messages again, but...

Perhaps it's got something to do with how the PNGs are created, because, although Opera 5 displays the ones I made in Xara X as intended, it backs the one ('Valid XHTML 1.0!') I got from the W3C with white, even though that one works fine in both IE 5.5 and Netscape 6.

Peter

[Klaus Nordby]

"All fine in Internet Explorer 5.5" Weird! According to my investigations, 32 bit PNGS do NOT display transparency in IE 5.5!

Just to add to the mysteries.


K

[pduggan]

Never thought to say that all the PNGs on my site are either 4 bit (16 colour) or 8 bit (256 colour). Another quick test suggests that 8 bit transparent PNGs don't come out transparent in any browser I've got (thanks, Klaus), so it might only be 4 bit that are at all reliable. Haven't had time to try anything more because I've got to get up and go to work!

Peter

[This message was edited by Peter Duggan on February 25, 2001 at 11:31 PM.]

[Sean Sedwards]

Peter

Send me /post some demo pngs that do and don't work (perhaps the same image created in different apps & colour depth). Doing that might resolve the issue enough for you in itself, however I'd be interested to strip the files apart.

Regards - Sean

[pduggan]

Here we go then (all supposedly transparent, created with Xara X, and it might be interesting to hear how these actually display in everyone's browsers):

http://www.petestack.com/forum/home4bw.pngHome (4 bit, browser, anti-aliased to white)<br clear="all">
http://www.petestack.com/forum/home8bw.pngHome (8 bit, browser, anti-aliased to white)<br clear="all">
http://www.petestack.com/forum/home4on.pngHome (4 bit, optimised, anti-aliased to navy)<br clear="all">
http://www.petestack.com/forum/home8on.pngHome (8 bit, optimised, anti-aliased to navy)<br clear="all">

Quoted from Xara X Help:

<blockquote>Transparent PNG Files

PNG format supports two types of transparency:
<ul>
<LI>(For formats up to 256 colors) a simple on-off transparency. By default, areas not covered by objects are exported as transparency. However you can also select a color in the Export dialog box and make that transparent if you wish. To enable transparency select the Transparent option in the dialog box when you export the PNG file.
<LI>(For true color format) graduated ("alpha-channel") transparency. This preserves any transparency you applied using the Transparency Tool. To enable alpha-channel transparency select True color + Alpha in the Export dialog box.[/list]</blockquote>

Cheers
Peter

PS Just been testing this page, and they all seem to display as transparent PNGs in IE 5.5, Opera 5 and Netscape 6, but not Netscape 4.7!

[This message was edited by Peter Duggan on February 26, 2001 at 11:18 AM.]

[Jonathan Payne]

Hi,

If you are interested in which types of PNG files different browsers support, you might like to have a look at this page - it has test images for all PNG file formats. Xara X can import all of these files (except the corrupted files).

PNG actually supports two kinds of transparency, alpha transparency where a red, green, blue and transparency level is stored for each pixel and paletted transparency where each palette entry specifies a red, green, blue and transparency value and each pixel is then a reference to an entry in the palette. This means that a paletted (normally a 256 colour PNG) can use multiple transparent colours of different transparency levels (this site give some more details). Very little software supports multiple transparent colours in a paletted image and while Xara X can import these images, it can't export them.

Even with the limitations of some browsers PNG support, PNG is still one of the best formats for the web as it has support for a wide range of file formats and is free from any patent issues.

Jonathan

[pduggan]

Thanks for that, Jonathan...

It was advice about the patent situation that led me to prefer PNGs to GIFs in the first place!

Peter