[Mapserver-users] TRANSPARENCY problem

Mon Mar 10 13:46:36 PST 2003

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Aaron -

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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:

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PROCESSING "COLOR_MATCH_THRESHOLD=3D3"

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To the LAYER block for the orthos.  Alternatively, use the OUTPUTFORMAT
option to create a 24-bit output image.

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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.

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            - Ed

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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>

-----Original =
Message----- 
From: Aaron D. Hunt
[mailto:hunt at zedxinc.com] 
Sent: Monday, March 10, =
2003 3:39
PM 
To:
mapserver-users at lists.gis.umn.edu 
Subject: =
[Mapserver-users]
TRANSPARENCY problem

<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>

</div>

</div>

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