[mapserver-users] strange png alpha behavior

[Charlton Galvarino]

Hi, all.  I'm stumped, and I've tried everything I can think of.  Rebuilding gdal, rebuilding libpng, rebuilding mapserver.  Even the version of mapserver doesn't really matter to me, but I have tried the latest and greatest.

MapServer version 5.2.0 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=FREETYPE SUPPORTS=ICONV SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=GEOS INPUT=EPPL7 INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE

If I pass b.png thru a normal WMS request, it looks beautimous.  If I pass a, it is incorrect.  a.png and b.png were made on different boxes against the same source data, and in spite of my best efforts to make those boxes' builds identical wrt gdal, ogr, etc. something is still different.

for b . . .

Driver: PNG/Portable Network Graphics
Files: /home/charlton/Temp/b.png
Size is 640, 720
Coordinate System is `'
Origin = (-100.003428819444423,49.999956597222223)
Pixel Size = (0.062413194444444,-0.062413194444444)
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (-100.0034288,  49.9999566)
Lower Left  (-100.0034288,   5.0624566)
Upper Right ( -60.0589844,  49.9999566)
Lower Right ( -60.0589844,   5.0624566)
Center      ( -80.0312066,  27.5312066)
Band 1 Block=640x1 Type=Byte, ColorInterp=Red
  Mask Flags: PER_DATASET ALPHA
Band 2 Block=640x1 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET ALPHA
Band 3 Block=640x1 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET ALPHA
Band 4 Block=640x1 Type=Byte, ColorInterp=Alpha

for a . . .

Driver: PNG/Portable Network Graphics
Files: /home/charlton/Temp/a.png
Size is 640, 720
Coordinate System is `'
Origin = (-100.003428819444423,49.999956597222223)
Pixel Size = (0.062413194444444,-0.062413194444444)
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (-100.0034288,  49.9999566)
Lower Left  (-100.0034288,   5.0624566)
Upper Right ( -60.0589844,  49.9999566)
Lower Right ( -60.0589844,   5.0624566)
Center      ( -80.0312066,  27.5312066)
Band 1 Block=640x1 Type=UInt16, ColorInterp=Red Band 2 Block=640x1 Type=UInt16, ColorInterp=Green Band 3 Block=640x1 Type=UInt16, ColorInterp=Blue Band 4 Block=640x1 Type=UInt16, ColorInterp=Alpha

I don't know enough about PNG to know what PER_DATASET ALPHA is.  But is this what might be upsetting the final product?

Plugging a or b into udig directly looks fine, and the a,b images look great.  But you can see that after I pass it thru a WMS request, I get bad_output.png.

Any ideas?

TIA,

Charlton





Charlton Galvarino
1 (803) 233-6205 : voice
1 (803) 223-9579 :   fax
charlton at 2creek.com

P.O. Box 50960
Columbia, SC 29250
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