[Mapserver-users] PNG Transparency in Internet Explorer -Solution

Fri Dec 19 11:30:07 EST 2003

Dave -

I have not needed to work around the issue because I don't need to
generate output images with transparency.  Obviously, some folks do, but
I haven't and therefore haven't had the problem.  As far as I'm aware,
this is the best available solution for the IE problem.

	- Ed

-----Original Message-----
From: Lowther, David W [mailto:dlowther at ou.edu] 
Sent: Friday, December 19, 2003 9:13 AM
To: Ed McNierney; Doug Cates; Lowther, David W
Cc: mapserver-users at lists.gis.umn.edu
Subject: RE: [Mapserver-users] PNG Transparency in Internet Explorer
-Solution

Ed,

Have you worked around this issue in any other way or does this seem
like the best possible solution at this time?

Dave

> -----Original Message-----
> From: Ed McNierney [mailto:ed at topozone.com]
> Sent: Thursday, December 18, 2003 7:32 PM
> To: Doug Cates; Lowther, David W
> Cc: mapserver-users at lists.gis.umn.edu
> Subject: RE: [Mapserver-users] PNG Transparency in Internet Explorer 
> -Solution
> 
> 
> Doug -
> 
> 1. This fix uses the AlphaImagerLoader filter that is part of Internet

> Explorer 5.5 and above (note: that means this fix only works on IE 5.5

> and above, so check your clients).  It is a client problem and a 
> client fix, so it is independent of the Web server.  The problem, of 
> course, is also independent of the Web server.
> 
> 2. Well, 32-bit PNGs, actually, because it's the alpha-channel that 
> doesn't work and is fixed by this DirectX-based filter.  In some cases

> - like hillshaded topos or color infrared DOQQs, 8-bit output is a 
> serious limitation and produces unacceptable results, so mandating 
> 8-bit output isn't always practical.
> 
> 	- Ed
> 
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com
> ed at topozone.com
> 
> 
> -----Original Message-----
> From: Doug Cates [mailto:doug at moximedia.com]
> Sent: Thursday, December 18, 2003 5:48 PM
> To: Lowther, David W
> Cc: mapserver-users at lists.gis.umn.edu
> Subject: Re: [Mapserver-users] PNG Transparency in Internet Explorer 
> -Solution
> 
> David,
> 
> 1. Is this an IIS server only solution, or will it work with other 
> engines?
> 
> 2. Isn't it only 24-bit PNG that browsers have trouble with? 
> If so, USGS should output the images in 8-bit PNG or GIF in order for 
> their services to be as interoperable as possible.
> The same holds true for people publixhing WMS services using 
> MapServer.
> 
> Doug
> 
> 
> 
> On Thu, 2003-12-18 at 12:59, Lowther, David W wrote:
> > Hi List,
> > 
> > Thought this might prove useful to someone...
> > 
> > Problem:
> > 
> > Internet Explorer does not correctly render transparency in PNG 
> > images.
> > 
> > Solution:
> > 
> > This needs to go in the <head> of the HTML file that will display a
> > PNG:
> > 
> > <style type="text/css">
> > img { behavior: url("pngbehavior.htc"); } </style>
> > 
> > Alternatively, the following line may be included in a CSS
> > (Stylesheet) that is used by the page:
> > img { behavior: url("pngbehavior.htc"); }
> > 
> > It is only required by Internet Explorer, but will not
> cause problems
> > in other browsers.
> > 
> > Also, the attached pngbehaviour.htc file must be present in the 
> > directory of the HTML files displaying PNG images and the
> spacer.gif
> > must be accessible to the pngbehaviour.htc script (default is 
> > images/spacer.gif).
> > 
> > 
> > <<pngbehavior.zip>>  <<spacer.zip>>
> > 
> > We came across this issue when using Mapserver as our WMS
> for the USGS
> 
> > National Map. Our layers obscured everything below them in Internet 
> > Explorer, but were correctly transparent in Mozilla. When USGS 
> > implements this things should be OK in Internet Explorer also.
> > 
> > 
> > David Lowther
> > Software Engineer
> > GEO Information Systems
> > University of Oklahoma
> > dlowther at ou.edu
> > (405) 325-3131
> > http://www.geo.ou.edu
> > 
> > 
> > 
> 
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