1前言
用GraphicsMagick处理svg转png，且背景是透明且没有黑边，由于使用虚拟机的gm版本是1.3.28导致有黑边问题且svg中path中有opacity属性时，加上+antialias也无效,直接使用1.3.31版本就OK了
2 正文
2.1 gm1.3.28版本
gm1.3.28 版本有bug
GraphicsMagick 1.3.28 2018-01-20 Q16 http://www.GraphicsMagick.org/
Copyright (C) 2002-2018 GraphicsMagick Group.
Additional copyrights and licenses apply to this software.
See http://www.GraphicsMagick.org/www/Copyright.html for details.
1.默认转成png格式图片，会默认黑底
//以下三种是等价命令
gm convert -background none img.svg output.png gm convert -background transparent img.svg output.png gm convert -background "#000000ff" img.svg output.png
2.若需要边框是其它颜色的代码（例如蓝色）如下：
gm convert -background "#00ff00ff" img.svg output.png
3.若设置颜色和图形边界颜色一样且path中的属性opacity存在，即使等于1（完全不透明），都会有默认黑色边框
gm convert +antialias -background none img.svg output.png
4.若设置颜色和图形边界颜色一样且path中的属性opacity不存在，即使等于1（完全不透明）也要去除改属性，则没有其它杂色边框
//+antialias 去除 除锯齿功能，则会把锯齿边颜色直接去掉，反之会默认补黑边，除非指定颜色
gm convert +antialias -background none img.svg output.png
5.左图使用-background "#00ff00ff",右图使用+antialias -background none
2.gm1.3.31版本
gm1.3.31 版本则直接使用
gm convert -background none img.svg output.png
就可以的，完美svg转png且保存背景透明
3 小结
gm要使用最新版本，切记！
附注：
svg原图的内容如下：
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47.531,-31 Q 49.656,-31 52.391,-31 L 63.469,-31 Q 65.75,-31 69.547,-31 Q 69.25,-28 69.391,-27 L 69.391,-21 Q 69.25,-18 69.703,-17 Q 66.812,-17 65.609,-17 L 51.172,-17 Q 49.656,-17 47.375,-17 Q 47.688,-19 47.688,-21 L 47.688,-27 Q 47.688,-28 47.531,-31 M 96.281,-8 L 85.047,-8 L 82.156,0 L 78.359,0 L 88.828,-28 L 93.094,-28 L 103.109,0 L 99.016,0 L 96.281,-8 M 86.25,-11 L 94.906,-11 L 90.812,-24 L 90.656,-24 L 86.25,-11 M 123.906,-7 L 119.812,-7 L 119.812,0 L 116.469,0 L 116.469,-7 L 104.469,-7 L 104.469,-10 L 116.922,-27 L 119.812,-27 L 119.812,-10 L 123.906,-10 L 123.906,-7 M 116.312,-22 L 107.656,-10 L 116.469,-10 L 116.469,-22 L 116.312,-22 ' transform="translate(-4,150) scale(1.5)" /> </g> </svg>