imagemagick-查找透明png轮廓的坐标(非边框) [英] imagemagick - find coordinates of outline of transparent png (not border)

问题描述

虽然很容易在视觉上绘制轮廓，但是imagemagick是否可以输出透明图像轮廓的坐标?

While it's easily done to visually outline, is it possible to have imagemagick output the coordinates of the outline of a transparent image?

请注意，通过轮廓线，我不仅指边界框的边界，还指任意形状的透明图像几何体周围的实际轮廓.

Note, by outline, I don't mean just the bounding box border, but the actual contour around an arbitrarily shaped transparent image geometry.

推荐答案

假设您从这张具有透明背景的图片开始:

Let's say you start with this image, which has a transparent background:

您可以提取透明度并找到边缘，如下所示:

You can extract the transparency and find the edges like this:

convert penguin.png -alpha extract -edge 1 -threshold 50% edges.png

如果要获取轮廓坐标(即白色像素)的列表而不是图像，则可以执行以下操作:

If, rather than an image, you want a list of the coordinates of the contour (i.e. the white pixels), you could do this instead:

convert penguin.png -alpha extract -edge 1 -threshold 50% -depth 8 txt: | awk -F: '/white/{print $1}'
256,0
253,1
254,1
255,1
257,1
258,1
259,1
253,2
259,2
252,3
253,3
...
...

用 more 替换 awk 及其之后的所有内容，以查看 awk 的实际作用-它只是打印每个像素的坐标那是白色的.

Replace awk and everything after it with more to see what the awk is actually doing - it is just printing the coordinates of every pixel that is white.

以上像素按行顺序显示，不像相邻像素一起显示的轮廓.如果需要，您可能更喜欢使用 potrace 这样的透明度生成SVG，如下所示:

The above pixels come out in row order, not like a contour where adjacent pixels come out together. If you want that, you might prefer to generate an SVG of the transparency with potrace like this:

convert penguin.png -alpha extract -threshold 50% pgm:- | potrace - --svg < alpha.pgm > result.svg

输出

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
 "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
<svg version="1.0" xmlns="http://www.w3.org/2000/svg"
 width="500.000000pt" height="577.000000pt" viewBox="0 0 500.000000 577.000000"
 preserveAspectRatio="xMidYMid meet">
<metadata>
Created by potrace 1.13, written by Peter Selinger 2001-2015
</metadata>
<g transform="translate(0.000000,577.000000) scale(0.100000,-0.100000)"
fill="#000000" stroke="none">
<path d="M0 3294 l0 -2476 25 16 c31 20 104 21 152 1 20 -8 38 -14 40 -12 2 2
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<path d="M4971 3138 c-20 -33 -89 -96 -165 -153 -23 -17 -103 -92 -179 -168
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</svg>

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