[Mapserver-users] TRANSPARENCY problem
Ed McNierney
ed at topozone.com
Mon Mar 10 16:46:36 EST 2003
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Aaron -
=20
This subject was just discussed on this list - the title was
"COLOR_MATCH_THRESHOLD"
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If you are using GDAL to read your source raster data, add:
=20
PROCESSING "COLOR_MATCH_THRESHOLD=3D3"
=20
To the LAYER block for the orthos. Alternatively, use the OUTPUTFORMAT
option to create a 24-bit output image.
=20
The basic problem is that you're running out of colors. Your original
grayscale color image is (presumably) a 256-color (256 shades of gray)
image, and MapServer uses almost all available colors in an 8-bit
paletter to render it. When it comes time to create NEW colors by
blending the highlight, there's no room.
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Think of it this way - a 256-color grayscale image with a transparent
red overlay can create up to 256 MORE colors, meaning a total of 512.
=20
- Ed
=20
Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA 01863
Phone: (978) 251-4242 Fax: (978) 251-1396
ed at topozone.com
=20
-----Original Message-----
From: Aaron D. Hunt [mailto:hunt at zedxinc.com]=20
Sent: Monday, March 10, 2003 3:39 PM
To: mapserver-users at lists.gis.umn.edu
Subject: [Mapserver-users] TRANSPARENCY problem
=20
When I try to do a transparency of 50 on a ortho background with a red
polygon I get the attached?=20
=20
=20
Aaron D. Hunt
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<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Aaron –</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>This subject was just discussed on this list – =
the title
was “COLOR_MATCH_THRESHOLD”</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>If you are using GDAL to read your source raster =
data, add:</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal style=3D'text-indent:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>PROCESSING
"COLOR_MATCH_THRESHOLD=3D3"</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>To the LAYER block for the orthos. =
Alternatively, use
the OUTPUTFORMAT option to create a 24-bit output =
image.</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>The basic problem is that you’re running out of
colors. Your original grayscale color image is (presumably) a =
256-color
(256 shades of gray) image, and MapServer uses almost all available =
colors in
an 8-bit paletter to render it. When it comes time to create NEW =
colors
by blending the highlight, there’s no room.</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Think of it this way – a 256-color grayscale =
image
with a transparent red overlay can create up to 256 MORE colors, meaning =
a
total of 512.</span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> =
-
Ed</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<div>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>Ed McNierney</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>President and Chief =
Mapmaker</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>TopoZone.com / Maps a la carte, =
Inc.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>73 Princeton Street, Suite =
305</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>North Chelmsford, MA =
01863</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>Phone: (978) 251-4242 Fax: =
(978)
251-1396</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'>ed at topozone.com</span></font></p>
</div>
<p class=3DMsoNormal><font size=3D2 color=3Dnavy face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DTahoma><span
style=3D'font-size:10.0pt;font-family:Tahoma'>-----Original =
Message-----<br>
<b><span style=3D'font-weight:bold'>From:</span></b> Aaron D. Hunt
[mailto:hunt at zedxinc.com] <br>
<b><span style=3D'font-weight:bold'>Sent:</span></b> Monday, March 10, =
2003 3:39
PM<br>
<b><span style=3D'font-weight:bold'>To:</span></b>
mapserver-users at lists.gis.umn.edu<br>
<b><span style=3D'font-weight:bold'>Subject:</span></b> =
[Mapserver-users]
TRANSPARENCY problem</span></font></p>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>When I try to do a =
transparency of
50 on a ortho background with a red polygon I get the =
attached? </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>Aaron D. =
Hunt</span></font></p>
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=00
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