[Mapserver-users] Raster support - JPG problem

[Lowell Filak]

Yes.
The format is reported readable & writeable via GDAL but the quality of the images (color) that I have seen once reduced to fit 8-bit were no good compared to the original tiffs.
That was prior to 24-bit color support in MS.
Lowell F.

The following message was sent by "Lowther, David W" <dlowther at ou.edu> on Thu, 16 Jan 2003 09:29:46 -0600.

> Have you guys considered ECW instead of JPEG?
> 
> -----Original Message-----
> From: Lowell Filak [mailto:lfilak at medinaco.org]
> Sent: Wednesday, January 15, 2003 3:57 PM
> To: Hankley, Chip; 'Zatorsky.MichaelP at police.qld.gov.au';
> mapserver-users at lists.gis.umn.edu
> Subject: RE: [Mapserver-users] Raster support - JPG problem
> 
> 
> I would have to agree with Chip's performance findings.
> We originally received all our orthophotography in TIFF format and planned
> on converting the images to JPEG to enable us to load the dataset on smaller
> machines.
> However the performance hit was major in every application (Mapserver,
> Arc/INFO, & Arcview) because the entire JPEG tile had to be decompressed
> before the software could determine which pixels of the image needed
> rendered.
> You can save space by flattening the source images to 8-bit WITH space
> reserved for 256 colors (some applications flatten to 8-bit but reserve
> space for 1000+ colors and that doesn't save any space).
> If truly needed you can always save space by resampling the data to a larger
> pixel size, ie. 1' -> 2'.
> Lowell F.
> 
> The following message was sent by "Hankley, Chip" <Chip.Hankley at GASAI.Com>
> on Wed, 15 Jan 2003 12:46:00 -0600.
> 
> > Michael,
> > 
> > As Norman and Daniel pointed out, there are known issues with JPEG and
> > MapServer.
> > 
> > That said, I had a similar problem some months back trying to serve up
> JPEG
> > images to MapServer. I did some experimenting and was finally able to get
> a
> > JPEG image to come up in MS (sorry, I can't remember exactly what I did),
> > but the performance was terrible.
> > 
> > My assumption is that MapServer has to somehow uncompress the JPEG images
> > before rendering them as part of the final image, and that this was the
> > cause of the performance hit (if I simply swapped the data source to a
> TIF,
> > there was no performance problem). I have no idea if my assessment of how
> > the mechanics of JPEG rendering is correct... but in the end, I concluded
> > that the trade-off for space savings with JPEG didn't make up for the
> > performance hit I was taking.
> > 
> > ...just my experience.
> > 
> > Chip
> > _______________________________________________
> > Mapserver-users mailing list
> > Mapserver-users at lists.gis.umn.edu
> > http://lists.gis.umn.edu/mailman/listinfo/mapserver-users
> 
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