[Ghostscript]裁剪pdf页面

hbghlyj

Linux下ghostscript的指令是gs, Windows下则是gswin32c.exe .(以下示例为linux)
首先用wget从Internet下载pdf文件到当前目录:

1. wget http://pcjohnson.net/312/Sqrt.pdf

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提取第9页到outfile_9.pdf

1. gs -sDEVICE=pdfwrite -dNOPAUSE -dBATCH -dSAFER -dFirstPage=9  -dLastPage=9 -sOutputFile=outfile_9.pdf Sqrt.pdf

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得到:

再进行裁剪.参数顺序:左框到原左框的距离121,下框到原下框的距离120,右框到原左框的距离523,上框到原下框的距离359. 单位都是postscript point,即1/72 inch.

1. gs -o cropped.pdf -sDEVICE=pdfwrite -c "[/CropBox [121 120 523 359]" -c " /PAGES pdfmark" -f outfile_9.pdf

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参考:stackoverflow.com/questions/6183479/cropping-a-pdf-using-ghostscript-9-01
再将pdf转换为svg

1. pdftocairo -svg cropped.pdf Sqrt.svg

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Sqrt.svg (38.23 KB, 下载次数: 88)

2022-5-18 01:10 上传

点击文件名下载附件

注1.
如果参数顺序错了,gs不会报错,但是会输出空的pdf(只有一条缝).如果使用pdfcrop,它就会报错
!!!Warning: Empty Bounding Box is returned by Ghostscript!
!!!   Page 1: 121 120 121 432
!!! Either there is a problem with the page or with Ghostscript.
!!! Recovery is tried by embedding the page in its original size.

注2.
另外,gs可以从pdf中分离image,vector,text三者.在这个例子中,“坐标轴”,“函数曲线”,“分数线”,“分隔线”都属于vector(矢量图).
参考:stackoverflow.com/questions/29657335/how-can-i-remove-all-images-from-a-pdf/37858893#37858893

关于“PDF”格式的资料:

Many PDF documents may contain vector artwork or line-art. However, due to the nature of PDF, it is not always possible for a computer program to determine where on a page such artwork occurs since each page is stored as a general mix of text, images and line-art.

hbghlyj

本楼将SVG附件转换为svg并替换附件

1. async function startconvert(){const url = $('attach_11673').firstElementChild.href;
2. const response = await fetch(url);
3. const decoder = new TextDecoder();
4. const reader = response.body.getReader();
5. str = '';
6. while (true) {
7. const { value, done } = await reader.read();
8. if (done) break;
9. str += decoder.decode(value);
10. }
11. $('attach_11673').parentNode.outerHTML = str}
12. startconvert()

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hbghlyj

developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Statements/async_function

async函数可能包含0个或者多个await表达式。await表达式会暂停整个async函数的执行进程并出让其控制权，只有当其等待的基于promise的异步操作被兑现或被拒绝之后才会恢复进程。

hbghlyj

在SumatraPDF中,按M可以显示光标位置, 再按M就会切换单位 (有mm,in,pt三种单位)
用in(英寸)的数值乘以72就得到bp的数值了


在Inkscape中,如果另存为optimized svg,在几何图中,标记顶点用的黑色的“圆点”就不见了,但是另存为“plain svg”是正常的.

hbghlyj

2022.08.11更新:
在1楼, 用"pdftocairo -svg cropped.pdf Sqrt.svg"替换了"pdf2svg cropped.pdf Sqrt.svg"
因为pdfsvg的作者写道:

Note: since this utility was written, the maintainers of Poppler have written a utility that works on the same principle: pdftocairo. I recommend that you use their utility since it is better maintained than mine.

他推荐用pdftocairo, 因为它比pdf2svg的维护得更好。

hbghlyj

Crop PDF files with Ghostscript
Normally, with the following command and justifications on the CropBox parameters, it should work.

1. gs -o cropped.pdf -sDEVICE=pdfwrite -dFirstPage=150 -dLastPage=180 -c "[/CropBox [100 100 500 500]" -f in.pdf

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in case the pdf file has no CropBox property, which can be checked with

1. pdfinfo in.pdf

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then the following command can be used instead

1. gs -o cropped.pdf -sDEVICE=pdfwrite -dFirstPage=150 -dLastPage=180 -dDEVICEWIDTHPOINTS=200 -dDEVICEHEIGHTPOINTS=250 -dFIXEDMEDIA -c "<</PageOffset [-21 -32]>> setpagedevice" -f in.pdf

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hbghlyj

Adobe Acrobat: Compress PDF online for free
Optimizing PDFs with Ghostscript By Ken Sharp - Thursday, September 29, 2022
How to compress PDF using ghostscript
I also added a function to my .bash_profile to make a shorthand that will compress and rename file.pdf to file.pdf.compressed.pdf:

1. pdfcompress ()
2. {
3.    gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dCompatibilityLevel=1.3 -dPDFSETTINGS=/screen -dEmbedAllFonts=true -dSubsetFonts=true -dColorImageDownsampleType=/Bicubic -dColorImageResolution=144 -dGrayImageDownsampleType=/Bicubic -dGrayImageResolution=144 -dMonoImageDownsampleType=/Bicubic -dMonoImageResolution=144 -sOutputFile=$1.compressed.pdf $1;
4. }

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use it: pdfcompress somefile.pdf