[ka-Map-users] PNG transparency in IE - some conclusions

Shoaib Burq hydromap at gmail.com
Mon Apr 10 09:56:19 EDT 2006

Well done Ehud, yea please can post the diffs... is there any reason
why the PNG's not created with alpha channel currently -- perhaps

On 4/9/06, Ehud Shabtai <eshabtai at gmail.com> wrote:
> Hi all,
> I just spent some hours playing with different PNG variants using
> ka-map and displaying them on IE.
> Here's what I learned:
> 1. IE supports PNG transparency for indexed color PNGs (i.e. not true
> color PNGs).
> 2. Using the famous hack, IE can display RGBA PNGs (the hack only
> works on true color with alpha channel PNG).
> ka-map point of view:
> The png files of ka-map's icons should be converted to indexed color
> to be displayed correctly. I converted the sun_white.png icon file and
> now it displays fine on IE.
> Displaying PNG layers with transparency on IE:
> This is possible if you use RGBA PNG (24 bits for colors + 8 bit for
> alpha channel).
> Some changes are required in ka-map:
> 1. tile.php - when it cuts a meta tile into the smaller tiles it does
> not copy the alpha channel. This should be changed so if the generated
> mapserver PNG image contains alpha channel it is copied to the tiles.
> 2. Currently the IE hack is never called in ka-map even for png files.
> In addition the actual hack must be issued after the image has been
> loaded (i.e. in kaMap_imgOnLoad), otherwise panning is really bad in
> IE.
> If there's interest i can provide my diffs.
> --
> Ehud Shabtai
> http://www.freemap.co.il/map/
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> ka-Map-users at lists.maptools.org
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