Mapserver/GD JPEGs

[Jeff Hoffmann]

Stephen Davies wrote:
> Last week I posted a request regarding comments in JPEGs and their 
> apparent effect on Motorola 3G telephones.
> 
> Since then I have found that a) the issue seems to affect all WAP phones 
> and b) it is not just comments that cause the problem.
> 
> It seems that these devices can only handle very simple images and those 
> generated by Mapserver/GD fall outside their capabilities.
> 
> I have found that, as well as removing the comments from my map images, 
> I have to go further.
> 
> My current work-around is to use a PERL script to generate the map image 
> to disk and then use the mogrify utility from Image Magik to "clean" 
> it. The mogrify command is simply:
> 
> mogrify -quality 100 image.jpg
> 
> but whatever this does to the image is enough to make it displayable on 
> a telephone when sent as an img src=.
> 
> If anybody knows more about what is happening here and/or what the 
> underlying problem is, I would love to hear it.

I don't really know a lot of details about what you're doing, but I do 
know that in my experience, phones don't like progressive JPEGs so I 
turn that option off (INTERLACE OFF for older versions or FORMATOPTION 
"INTERLACE=OFF" for newer versions that use an OUTPUTFORMAT block).  I 
think it's enabled by default, so if you don't have an INTERLACE 
setting, it's most likely creating progressive JPEGs.  (I'd guess 
mogrify may be re-encoding from progressive to non-progressive, and 
that's why you're seeing the behavior you're seeing.)


--
Jeff Hoffmann
Head Plate Spinner
PropertyKey.com