Images of formulas look shoddy when opened with gimp

[heber@…]

TracMathplugin (here 0.3) generates the formulas as tiny .png images embedded into the html page. These images look decent when viewed with browsers such as firefox (here 3.6.17). However, if one downloads the image and opens it up in image manipulator such as gimp, the image looks very grainy/pixelated. Only truely black pixel are visible, everything gray is lost (made transparent).

The problem can be remedied within gimp if the color palette (in the gimp menu, that's Image/Mode) is changed from indexed to rgb. Then suddenly gray pixels become visible.

I don't know how the pngs are rendered, so I am not much of a help here but hopefully the palette thing gives a clue to this.

[heber@…]

As a sidenote: I came upon this issue because I am using TracWikiPrintPlugin to generate PDFs from the TRAC pages as a sort layman's way to generate simple and pretty latex pages (we use it here for quickly generating sheets for a molecular dynamics tutorial). However, the formulas looked just plain ugly in the PDF while absolutely acceptable on the TRAC page.

[Kamil Kisiel]

This probably has to do with the png compression. It seems the plugin is using maximum compression for PNGs in order to save space. I can make a version where the compression level is configurable and you can see if setting it to a lower value helps.

[Kamil Kisiel]

Please try version 0.4 of the plugin, it includes a compression option in the [tracmath] section of the config file. You can set the option to a number from 1 - 9, where 1 is lower and 9 is higher. Let me know if it makes any difference.

[heber@…]

That does the trick, although I do not see any change in size of the images representing formulas when changing compression from 1 to 9.

There is one more thing: the formulas might become larger than desired on the webpage compared to a generated PDF (via TracWikiPrintPlugin). We patched your plugin as follows:

der patch:
--- tracmath/tracmath.py	2010-12-21 20:59:02.000000000 +0100
+++ tracmath/tracmath.py	2011-05-24 15:07:42.000000000 +0200
@@ -16,6 +16,7 @@
 from trac.web import IRequestHandler
 from trac.util import escape
 from trac import mimeview
+import Image

 __author__ = 'Reza Lotun'
 __author_email__ = 'rlotun@gmail.com'
@@ -170,8 +171,10 @@
             # Touch the file to keep it live in the cache
             os.utime(imgpath, None)

-        result = '<img src="%s/tracmath/%s" alt="%s" />' %
(req.base_url, imgname, content)
-        if label:
+	im=Image.open(imgpath)
+	height=im.size[1]
+	result = '<img src="%s/tracmath/%s" alt="%s" height="%spx"
class="formula"/>' % (req.base_url, imgname, content, int(height *(1/
(self.mag_factor/1200.0) *1.2) ))
+	if label:
             result = '<a name="%s">(%s)<a/>&nbsp;%s' % (label, label,
result)
         return result

@@ -200,7 +203,9 @@
         latex = '/usr/bin/latex'
         dvipng = '/usr/bin/dvipng'
         max_png = 500
-        mag_factor = 1200
+        #mag_factor = 1200
+	#see dvipng manpage -x for valid values
+        mag_factor = 2488

         if 'tracmath' not in self.config.sections():
             pass    # TODO: do something

That is we changed the variable mag_factor to adapt the size of the formulas to the size of rest of the text.

[Kamil Kisiel]

Glad to hear it worked for you, and thanks for the suggestion. I don't want to introduce a dependency on the Python Imaging Library so I think I'll leave it in your hands for now.

I should note that you can change the mag_factor option in trac.ini

[heber@…]

Thanks for looking into this bug and thanks for the great plugin!