[OpenLayers-Dev] Are there png8 wms tile problems with IE?

[Andrew Hughes]

Hi Louvy,

I've noticed that the png8's had a problem in several pieces of software...
not just IE. I suspect (and I do stress suspect) that this may be caused not
by a defective image or the inability of IE/Others to handle 8 bit png.. but
I think it has something to do with the HTTP response type of the image from
geoserver. Correct me if I am wrong... but "image/png8" is not an official
mime-type, its likely IE is getting confused by this. PNG was designed as a
wrapper to several compression formats... hence the name Portable Network
Graphics.

In IE, I noticed that I was getting black instead of transparency in the
image inside IE. Perhaps this is the same for you?

In the end, rather than use png (24)  or png8 I switched to gif.

--AH


On 9/21/07, louvy.joseph at gmail.com <louvy.joseph at gmail.com> wrote:
>
> I am cross posting this on both geoserver & openlayers lists..
>
> Recently I was enquiring if any of you have seen the exception issues
> with geoserver 1.5.3. I have further problems with 1.5.3, this time with
> PNG8.
>
> Is the png8 format rendered by geoserver-1.5.3 fully compliant with the
> PNG specs?  Please ignore my lack of knowledge on PNG. Are there any
> limitations or certain features not being implemented for this png8
> format? I am using Openalyers 2.4 on the client side. Everything is fine
> on firefox. But both IE6 & IE7 have problems with the  png8 produced by
> geoserver. This manifests in couple of ways:
>
> 1) Most of the times, the IE gets redirected to some other page when I
> use png8 format for openlayers wms layer. (If I use png instead of png8,
> everything is fine). I am hypothesizing that IE is not able to process
> the geoserver png8 and gets  confused.
>
> 2) Lot of times with png8, the openlayers lands in
> OpenLayers.Util.onImageLoadError() handler. Basically IE thinks that
> there is some problem with image URL; however the IE ends up drawing the
> WMS content of the png8 tile fine (but the tile soon gets replaced by a
> pink tile). Looks like IE thinks that there is something wrong with this
> tile even though it was able to render it fine. The problem does not
> consistently happen with one particular tile; the same tile on refresh
> comes out fine.
>
> The support for png8 is very very important for IE6 since IE6 can't
> handle PNG24 transparency.
>
> Any body has any ideas? Thanks in advance..
> Louvy Joseph
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