[thelist] PNG support in IE6

Mark Kennedy mark at eurogamer.net
Thu Nov 11 09:04:13 CST 2004

Quick tip for people wanting to experiment with PNGs.

<tip type="PNG Transparency">

PNG-24's give you multiple levels of opacity using an alpha channel, but 
are far too big for web use.  Did you know it's possible to quantise the 
  alpha channel when creating PNG-8's?  Adobe products don't (seem to) 
support this at all, however PNGQuant, which can be found here:


is a handy little tool for palletising PNG-24's into PNG-8's including 
the alpha channel.

Internet Explorer's support for these palletised alpha channels is bad, 
but better than it's non-support for PNG-24 alpha.  In IE, a pixel with 
less than 100% opacity will be rendered fully transparent.

This behaviour makes PNG-8's with quantised alpha channels useful for 
images where you just want an antialiased edge (or tacky drop shadow) 
and aren't too bothered if you get a jagged edge in IE.

For a (pretty awful) example of these in use see:


(please don't offer design criticism -- I know it's horrendous)

Here, PNG-8's are used for the floating logos and box shot.  An image 
rewriter behaviour is used to replace the PNG-8s with PNG-24s once the 
page is loaded.  The PNG-8's are already loaded and rendered at this 
point, so the rewriting occurs in the background while the user is 
reading the page.  This gives the impression that the shadows and smooth 
edges 'pop' into existence later on (more noticeable on a slow connection).

Hope that's useful.



Richard Bennett wrote:
> On Thursday 11 November 2004 00:21, Tim Burgan wrote:
>>Has anyone discovered away for transparent PNG support in IE6?
> You probably mean opacity, since transparency is already supported in IE.
> For opacity see: 
> http://webfx.eae.net/dhtml/pngbehavior/pngbehavior.html
> Cheers,
> Richard.

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