Legacy ImageMagick Discussions Archive

I get pretty strange output trying to generate outlined text with imagemagick, even for very simple commands:

convert -size 320x100 xc:black -gravity center -stroke black -fill white -strokewidth 1 -font Arial-Bold -pointsize 40 -annotate +0+0 "This is a bridge" output.png

Here it is zoomed in to the g in bridge:

Does anyone know what causes this kind of bleed-through?

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$ convert -version
Version: ImageMagick 6.7.7-10 2014-03-06 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2012 ImageMagick Studio LLC
Features: OpenMP

Thanks!

First your IM version 6.7.7.10 is ancient (about 150 versions old). You might get better results if you can upgrade.

The issue you see is from antialiasing, especially with a stroke added and one that is not the same as the fill color.

You will get a better result if you leave off the -stroke and -strokewidth

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convert -size 320x100 xc:black -gravity center -fill white -font Arial-Bold -pointsize 40 -annotate +0+0 "This is a bridge" output.png

or use a stroke color the same as the fill color

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convert -size 320x100 xc:black -gravity center -stroke white -fill white -strokewidth 1 -font Arial-Bold -pointsize 40 -annotate +0+0 "This is a bridge" output.png

or add +antialias to the command without the stroke and strokewidth

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convert -size 320x100 xc:black -gravity center -fill white -font Arial-Bold -pointsize 40 +antialias -annotate +0+0 "This is a bridge" output.png

Hi, fmw42;

This imagemagick version is whatever comes on the latest ubuntu LTS; that's what our servers are running. It would be difficult to upgrade our servers to a nonstandard version, but it's something I can look into if it fixes the issue. (can you reproduce it on the latest version?)

I'm not sure I understand your advice to leave off the stroke. In my actual program, this text will be rendered overtop of an arbitrary photograph instead of a black background, so I want to have an outline around the text to prevent it from blending into whatever features might be in that area of the photograph.

Thanks for the help!

I get the same results as you on IM 6.9.2.7 Q16. It is an anti-aliasing issue.

It is working correct at normal viewing size as far as I can see. Why do you need to enlarge the text to the point that the antialiasing is visible?

Add +antialias to remove the antialiasing gray. Here I put it on a transparent background. But it will look more blocky.

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convert -size 320x100 xc:none -gravity center -stroke black -fill white -strokewidth 1 -font Arial-Bold -pointsize 40 +antialias -annotate +0+0 "This is a bridge" output.png

The issue is very visible at normal size. I notice that some png rendering engines expose it to a lesser or greater extent. Firefox's seems to be pretty good; imagemagick's seems to be particularly bad.

Here I've opened the image with the 'display' command and took a screenshot of the results. The result seems pretty noticeable to me. Do you see it here?

No not really. I only see the smooth edges from the antialiasing. see https://en.wikipedia.org/wiki/Aliasing

You can inquire further from the developers on the Developer's forum.

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