That's why approaches such as antialiasing as so useful in resizing imagery. However while that'll give you an asthetically pleasing representation of a resampled raster (like a thumbnail), text labels won't be readable. Last time I looked, Mapserver used a fast (but less asthetic) nearest neighbor algorithm which would give exactly the result Gregor describes.
Sites like Google Maps know this and pre-generate/cache tiles at appropriate resolutions (from vectro data) so that text is rendered at an appropriate resolution. Scans of hardcopy maps will always be best really bad at handling text (there's no easy way to set appropriate scale thresholds for text pixels). We did some bathymetry soundings and they weren't too bad only because the text density wasn't high enough to drown out the non-text content. Something like a majority() image filter could be used to create an overview that sample out text (black) that is not going to be legible anyway. I'm not sure how much effort is needed; I'd like to think this is a legacy issue from the paper map era. Navigation charts are a bit unusual in that the chart is usually a legal document and experssing the legal concepts digitally has taken time. Cheers, Antti P.S. gdaltanslate will do pixel-by-pixel format conversion. Gdalwarp is a raster resampler and therefore by definition a potentially (very!) data destructive tool. Gregor may even be looking at two signiciant resampling events. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rahkonen Jukka Sent: Monday, 21 April 2008 3:30 PM To: Gregor Mosheh; mapserver-users@lists.osgeo.org Subject: Re: [mapserver-users] MapServer's image quality stinks serving uptheseNOAA NRCs Gregor Mosheh wrote: > URL http://ms2.geowake.com/ These were KAP files downloaded from NOAA's Raster Nautical Charts (NRCs), converted to TIFF with gdalwarp. > The image quality there stiiiinks! A second map (no longer available) made of the raw images sliced into PNGs and not run via MapServer, looks very nice. You can make out text in 1 zoom, the high-level maps are less grainy, the quality once you zoom in is better... > Any thoughts on why it'd be so ugly? The images almost look as if they've been downsized, don't they? Aren't they inevidently downsized if you are looking at the whole North American coastline with just something like 800 by 600 pixels on screen? I can see very similar ugly view when I fit on the screen a large OpenStreetMap map (12000 by 12000 pixels) rendered with a lot of details. The map begins to look nice once I zoom in such much that the labels come readable. I have been thinking that it is because the street names and other details every now and then makes some downsampled image pixel to appear black. For the algorithm it might be OK but for the one who is looking at the map it makes just noise. In your case there are whole lot of contour lines and depth values causing the noise. I guess that if you mosaic lots of image tiles together and open it with Photoshop or whatever else viewer your experience would not be much better. I don't believe you can improve the far-away zoom quality much with Mapserver. You may try to filter out digitally some depth values squeesed nos to one pixel only or try some other tricks, but I think that best you could do is to find out another map that is originally made to be be used at nationwide scale. -Jukka Rahkonen- _______________________________________________ mapserver-users mailing list mapserver-users@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/mapserver-users ------IMPORTANT - This message has been issued by The Department of Agriculture, Fisheries and Forestry (DAFF). The information transmitted is for the use of the intended recipient only and may contain confidential and/or legally privileged material. It is your responsibility to check any attachments for viruses and defects before opening or sending them on. Any reproduction, publication, communication, re-transmission, disclosure, dissemination or other use of the information contained in this e-mail by persons or entities other than the intended recipient is prohibited. The taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you have received this e-mail in error please notify the sender and delete all copies of this transmission together with any attachments. If you have received this e-mail as part of a valid mailing list and no longer want to receive a message such as this one advise the sender by return e-mail accordingly. Only e-mail correspondence which includes this footer, has been authorised by DAFF ------ _______________________________________________ mapserver-users mailing list mapserver-users@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/mapserver-users