问题描述
我正在尝试将pdf图转换为png或jpeg文件.原因是我想将图像用于演示，并且我需要这两种格式，它们具有完全相同的尺寸/缩放比例.
I'm trying to convert a pdf plot to a png or jpeg file.The reason is that I want to use the images for presentations and I need both formats, having exactly the same dimensions/scaling.
我尝试了动画包中的函数im.convert()，但是输出看起来真的很差，无论是png还是jpeg.
I tried the function im.convert() in the animation package, but the output looks really bad, in both png and jpeg.
要运行以下代码，您需要动画"程序包和ImageMagick软件( http://www.imagemagick.org/script/convert.php )
To be able to run the following code you need the "animation" package and the ImageMagick software (http://www.imagemagick.org/script/convert.php)
library("animation")
ani.options(outdir = getwd())
pdf("bm.pdf")
plot(1:10)
dev.off()
im.convert("bm.pdf", output = "bm.jpeg")
im.convert("bm.pdf", output = "bm.png")
推荐答案
im.convert的结果可能不令人满意，因为它使用默认分辨率，即74 dpi.您可以通过传递额外的参数来提高分辨率:
The result of im.convert is probably not satisfactory because it uses the default resolution, which is 74 dpi. You can increase the resolution by passing an extra parameter:
im.convert("bm.pdf", output = "bm.png", extra.opts="-density 150")
-density 150将使分辨率提高一倍，并且您的PNG和JPEG看起来会更好.
-density 150 will double the resolution and your PNGs and JPEGs will look nicer.
但是通常，最好使用png()和jpeg()生成图并使用适当的参数来获得与pdf()相同的结果.例如:
But in general it is probably better to use png() and jpeg() to generate the plots and use appropiate parameters to get the same results as with pdf(). For example:
pdf(width=5, height=5)
plot(1:10)
dev.off()
png(width=5, height=5, units="in", res=150)
plot(1:10)
dev.off()
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