将PDF转换为具有透明背景的PNG [英] Converting PDF to PNG with transparent background

问题描述

我们有一个Ruby on Rails应用程序，需要将PDF转换为具有透明背景的PNG.我们正在使用rmagick 2.13.1.在我们的开发机器上，以下代码可以完全按照我们的要求工作.

We have a Ruby on Rails application that needs to convert a PDF into a PNG with a transparent background. We're using rmagick 2.13.1. On our development machines the following code works exactly how we want it.

pages = Magick::Image.from_blob(book.to_pdf.render){ self.density = 300 }
page = pages[0]

image_file = Tempfile.new(['preview_image', '.png'])
image_file.binmode
image_file.write( page.to_blob { |opt| opt.format = "PNG" } )

然后我们保存image_file，所有内容都是桃红色的.但是，当我们部署到Heroku上的评论服务器时，生成的图像具有白色背景.事实证明，Heroku的雪松堆栈使用的是imagemagick ImageMagick 6.5.7-8 2010-12-02，我们在开发机器上使用的是ImageMagick 6.7.5-7 2012-05-08.

We thens save the image_file and all is peachy. When we deployed to a review server on Heroku, though, the generated image has a white background. It turns out that Heroku's cedar stack is using imagemagick ImageMagick 6.5.7-8 2010-12-02 where we're using ImageMagick 6.7.5-7 2012-05-08 on our development machines.

我已经在网上搜寻了较旧的帖子，这些帖子可能适用于较旧的版本，以尝试弄清楚如何生成透明的PNG.它肯定受支持，但是到目前为止，我还无法弄清楚设置的正确组合.

I've scoured the net for older posts that might apply to the older version to try and figure out how to generate the transparent PNGs. It's surely supported, but, so far I haven't been able to figure out the right combination of settings.

为验证不是问题的是PDF生成，我下载了在Heroku上生成的PDF，并使用上述代码(将其稍作修改以读取文件而不是生成文件)成功地将其转换为透明的PNG

To verify that it wasn't the PDF generation that was the problem, I downloaded a PDF generated on Heroku and successfully converted it using the above code (slightly modified to read the file in instead of generate it) to a transparent PNG.

我尝试过各种组合的一些东西是:

Some of the things I've tried in various combinations are:

• page.matte = true
• page.format = "PNG32"
• page.background_color = "none"
• page.transparent_color = "white"
• page.transparent("white")

• page.matte = true
• page.format = "PNG32"
• page.background_color = "none"
• page.transparent_color = "white"
• page.transparent("white")

因此，问题是这可能吗?".如果是这样，在写出图像之前我需要在图像上进行哪些设置?

So, the question is "is this possible?". If so, which settings do I need to set on the image before writing it out?

我还正在研究在Heroku上包含更新的Imagemagick的已编译二进制文件.

I'm also investigating including a compiled binary of a more up to date Imagemagick on Heroku.

感谢您的帮助.

推荐答案

这不再是问题，因为Heroku在其各个堆栈上都有ImageMagick 6.7-6.9版本.

This should no longer be an issue, as Heroku has ImageMagick versions 6.7-6.9 on their various stacks.

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