If you want to give Cairo a try, you could modify mapcairo.c like this:
diff --git a/mapcairo.c b/mapcairo.c
index 0f4cc094..d28947d6 100644
--- a/mapcairo.c
+++ b/mapcairo.c
@@ -517,6 +517,12 @@ imageObj* createImageCairo(int width, int height,
outputFormatObj *format,colorO
cairo_set_line_cap (r->cr,CAIRO_LINE_CAP_ROUND);
cairo_set_line_join(r->cr,CAIRO_LINE_JOIN_ROUND);
+ {
+ const char* antialias = msGetOutputFormatOption(format, "ANTIALIAS",
"TRUE");
+ if (EQUAL(antialias, "OFF") || EQUAL(antialias, "FALSE") ||
EQUAL(antialias, "0")) {
+ cairo_set_antialias(r->cr, CAIRO_ANTIALIAS_NONE);
+ }
+ }
image->img.plugin = (void*)r;
} else {
msSetError(MS_RENDERERERR, "Cannot create cairo image of size %dx%d.",
This adds a FORMATOPTION "ANTIALIAS" to the CAIRO/*-Drivers that defaults to
TRUE. But when explicitly set to 0/OFF/FALSE it calls cairo_set_antialias() to
disable it. The raster buffer created by the CAIRO renderer is passed to the
PNG writer which enables COMPRESSION, PALETTE_FORCE, QUANTIZE_FORCE. So you can
combine it:
OUTPUTFORMAT
NAME "cairopng"
DRIVER CAIRO/PNG
MIMETYPE "image/png"
IMAGEMODE RGB
EXTENSION "png"
FORMATOPTION "ANTIALIAS=FALSE"
FORMATOPTION "QUANTIZE_FORCE=ON"
FORMATOPTION "QUANTIZE_COLORS=256"
FORMATOPTION "COMPRESSION=9"
END
I used the msautotest/renderers/line_simple.map example to test and that
crushed the resulting png from 5920 bytes down to 947 bytes.
HTH, Andreas
-----Ursprüngliche Nachricht-----
Von: Richard Greenwood <richard.greenw...@gmail.com>
Gesendet: Mittwoch, 19. Mai 2021 16:12
An: Eichner, Andreas - SID <andreas.eich...@sid.sachsen.de>
Cc: mapserver <mapserver-users@lists.osgeo.org>
Betreff: Re: [mapserver-users] anti-aliasing (was differing image size with
different mapserver versions)
Andreas,
I have built a version of MapServer without AA enabled in mapagg.cpp as you
have suggested. The reduction in file size is remarkable. In some cases it is
1/2 the size of a GD/GIF or an optimized AGG/PNG8. Aesthetically the images are
pretty bad at first, but by softening the colors in the map file and reducing
the color contrast between adjacent features I'm getting images that are
acceptable. I will try experimenting with Cairo driver modifications next.
Thank you very much for your suggestion and detailed explanation.
Rich
On Wed, May 19, 2021 at 5:38 AM Eichner, Andreas - SID
<andreas.eich...@sid.sachsen.de <mailto:andreas.eich...@sid.sachsen.de> > wrote:
What AGG does with it's sub-pixel accuracy can be viewed as computing
the contribution of the pixels of a virtually larger image to the pixels of the
final image. It uses a gamma function to translate the amount of virtual pixels
into an amount of visual impact on the final pixel - both expressed as a value
in the range 0..1. AGG's default is a linear function that proportionally maps
the range 0..1 onto 0..1 (i.e. y=x). MapServer (where applied) uses a linear
gamma function that proportionally maps the range 0..gamma onto 0..1. All this
results in intermediate color values giving a smoother and visually improved
result as in this example:
https://commons.wikimedia.org/wiki/File:Antialiasing.png#/media/Datei:Antialiasing.png
As PNG uses lossless compression these additional information enlarges
the resulting files. So to reduce the size of your map image files it's best to
turn anti-aliasing off. One way is to compile a special version with modified
typedefs in mapagg.cpp to turn AA off. With Cairo you could use the method
cairo_set_antialias(cairo_t*, CAIRO_ANTIALIAS_NONE) to switch it off. But then
you would loose paletted image and compression control.
With the modified AGG you should still apply the other suggestions with
reduced palette and maximum compression.
HTH
-----Ursprüngliche Nachricht-----
Von: mapserver-users <mapserver-users-boun...@lists.osgeo.org
<mailto:mapserver-users-boun...@lists.osgeo.org> > Im Auftrag von Richard
Greenwood
Gesendet: Dienstag, 18. Mai 2021 18:50
An: mapserver <mapserver-users@lists.osgeo.org
<mailto:mapserver-users@lists.osgeo.org> >
Betreff: [mapserver-users] anti-aliasing (was differing image size with
different mapserver versions)
Thanks to several helpful replies to my previous thread I know that the
increased image size between MapServer 6 with the GD driver and MapServer 7
with the AGG driver is due to differences in anti-aliasing (and lack of) in the
two drivers. (AGG features anti-aliasing and sub-pixel resolution
<https://en.wikipedia.org/wiki/Anti-Grain_Geometry> ).
Gamma setting from 0-1 affects the size of a filled polygon layer by a
factor of almost 3x. But gamma has no effect on text, lines, and polygon
outlines. So images comprised of these types of features are approximately 2x
larger with the AGG/PNG8 driver than with the GD/GIF driver.
Where else should I be looking to reduce my images sizes? I serve rural
areas with poor internet so in my case, smaller image sizes are more important
than higher quality images.
Thanks,
Rich
--
Richard W. Greenwood, PLS
www.greenwoodmap.com <http://www.greenwoodmap.com>
<http://www.greenwoodmap.com>
--
Richard W. Greenwood, PLS
www.greenwoodmap.com <http://www.greenwoodmap.com>
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