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如何将彩色pdf转换为黑白pdf？

tag-icon • tag-icon pdf imagemagick ghostscript color-management
如何将彩色pdf转换为黑白pdf？

我想将一个带有一些彩色文本和图像的pdf转换为另一个只有黑白的pdf，以减少其尺寸。此外，我想将文本保留为文本，而不转换图片中的页面元素。我尝试了以下命令：

convert -density 150 -threshold 50% input.pdf output.pdf

在另一个问题中发现，一条链接，但它做了我不想要的事情：输出中的文本被转换成糟糕的图像，并且不再可选。我尝试使用 Ghostscript：

gs      -sOutputFile=output.pdf \
        -q -dNOPAUSE -dBATCH -dSAFER \
        -sDEVICE=pdfwrite \
        -dCompatibilityLevel=1.3 \
        -dPDFSETTINGS=/screen \
        -dEmbedAllFonts=true \
        -dSubsetFonts=true \
        -sColorConversionStrategy=/Mono \
        -sColorConversionStrategyForImages=/Mono \
        -sProcessColorModel=/DeviceGray \
        $1

但它给了我以下错误消息：

./script.sh: 19: ./script.sh: output.pdf: not found

还有其他方法来创建该文件吗？

答案1

GS 示例

gs您上面运行的命令有一个尾随，$1通常用于将命令行参数传递到脚本中。所以我不确定您实际尝试过什么，但我猜测您尝试将该命令放入脚本中script.sh：

#!/bin/bash

gs      -sOutputFile=output.pdf \
        -q -dNOPAUSE -dBATCH -dSAFER \
        -sDEVICE=pdfwrite \
        -dCompatibilityLevel=1.3 \
        -dPDFSETTINGS=/screen \
        -dEmbedAllFonts=true \
        -dSubsetFonts=true \
        -sColorConversionStrategy=/Mono \
        -sColorConversionStrategyForImages=/Mono \
        -sProcessColorModel=/DeviceGray \
        $1

并像这样运行它：

$ ./script.sh: 19: ./script.sh: output.pdf: not found

不确定如何设置此脚本，但它需要可执行。

$ chmod +x script.sh

不过这个脚本肯定有什么不对劲的地方。当我尝试它时，我得到了这个错误：

不可恢复的错误：.putdeviceprops 中的 rangecheck

替代

我会使用 SU 问题中的这个脚本来代替该脚本。

#!/bin/bash

gs \
 -sOutputFile=output.pdf \
 -sDEVICE=pdfwrite \
 -sColorConversionStrategy=Gray \
 -dProcessColorModel=/DeviceGray \
 -dCompatibilityLevel=1.4 \
 -dNOPAUSE \
 -dBATCH \
 $1

然后像这样运行它：

$ ./script.bash LeaseContract.pdf 
GPL Ghostscript 8.71 (2010-02-10)
Copyright (C) 2010 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
Processing pages 1 through 2.
Page 1
Page 2

答案2

我找到了一个脚本这里可以做到这一点。它要求gs你似乎拥有但也pdftk。您没有提到您的发行版，但在基于 Debian 的系统上，您应该能够使用以下命令安装它

sudo apt-get install pdftk

您可以找到它的 RPM这里。

安装后pdftk，将脚本另存为graypdf.sh并运行，如下所示：

./greypdf.sh input.pdf

它将创建一个名为input-gray.pdf.我在此处包含整个脚本以避免链接失效：

# convert pdf to grayscale, preserving metadata
# "AFAIK graphicx has no feature for manipulating colorspaces. " http://groups.google.com/group/latexusersgroup/browse_thread/thread/5ebbc3ff9978af05
# "> Is there an easy (or just standard) way with pdflatex to do a > conversion from color to grayscale when a PDF file is generated? No." ... "If you want to convert a multipage document then you better have pdftops from the xpdf suite installed because Ghostscript's pdf to ps doesn't produce nice Postscript." http://osdir.com/ml/tex.pdftex/2008-05/msg00006.html
# "Converting a color EPS to grayscale" - http://en.wikibooks.org/wiki/LaTeX/Importing_Graphics
# "\usepackage[monochrome]{color} .. I don't know of a neat automatic conversion to monochrome (there might be such a thing) although there was something in Tugboat a while back about mapping colors on the fly. I would probably make monochrome versions of the pictures, and name them consistently. Then conditionally load each one" http://newsgroups.derkeiler.com/Archive/Comp/comp.text.tex/2005-08/msg01864.html
# "Here comes optional.sty. By adding \usepackage{optional} ... \opt{color}{\includegraphics[width=0.4\textwidth]{intro/benzoCompounds_color}} \opt{grayscale}{\includegraphics[width=0.4\textwidth]{intro/benzoCompounds}} " - http://chem-bla-ics.blogspot.com/2008/01/my-phd-thesis-in-color-and-grayscale.html
# with gs:
# http://handyfloss.net/2008.09/making-a-pdf-grayscale-with-ghostscript/
# note - this strips metadata! so:
# http://etutorials.org/Linux+systems/pdf+hacks/Chapter+5.+Manipulating+PDF+Files/Hack+64+Get+and+Set+PDF+Metadata/
COLORFILENAME=$1
OVERWRITE=$2
FNAME=${COLORFILENAME%.pdf}
# NOTE: pdftk does not work with logical page numbers / pagination;
# gs kills it as well;
# so check for existence of 'pdfmarks' file in calling dir;
# if there, use it to correct gs logical pagination
# for example, see
# http://askubuntu.com/questions/32048/renumber-pages-of-a-pdf/65894#65894
PDFMARKS=
if [ -e pdfmarks ] ; then
PDFMARKS="pdfmarks"
echo "$PDFMARKS exists, using..."
# convert to gray pdf - this strips metadata!
gs -sOutputFile=$FNAME-gs-gray.pdf -sDEVICE=pdfwrite \
-sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray \
-dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH "$COLORFILENAME" "$PDFMARKS"
else # not really needed ?!
gs -sOutputFile=$FNAME-gs-gray.pdf -sDEVICE=pdfwrite \
-sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray \
-dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH "$COLORFILENAME"
fi
# dump metadata from original color pdf
## pdftk $COLORFILENAME dump_data output $FNAME.data.txt
# also: pdfinfo -meta $COLORFILENAME
# grep to avoid BookmarkTitle/Level/PageNumber:
pdftk $COLORFILENAME dump_data output | grep 'Info\|Pdf' > $FNAME.data.txt
# "pdftk can take a plain-text file of these same key/value pairs and update a PDF's Info dictionary to match. Currently, it does not update the PDF's XMP stream."
pdftk $FNAME-gs-gray.pdf update_info $FNAME.data.txt output $FNAME-gray.pdf
# (http://wiki.creativecommons.org/XMP_Implementations : Exempi ... allows reading/writing XMP metadata for various file formats, including PDF ... )
# clean up
rm $FNAME-gs-gray.pdf
rm $FNAME.data.txt
if [ "$OVERWRITE" == "y" ] ; then
echo "Overwriting $COLORFILENAME..."
mv $FNAME-gray.pdf $COLORFILENAME
fi
# BUT NOTE:
# Mixing TEX & PostScript : The GEX Model - http://www.tug.org/TUGboat/Articles/tb21-3/tb68kost.pdf
# VTEX is a (commercial) extended version of TEX, sold by MicroPress, Inc. Free versions of VTEX have recently been made available, that work under OS/2 and Linux. This paper describes GEX, a fast fully-integrated PostScript interpreter which functions as part of the VTEX code-generator. Unless specified otherwise, this article describes the functionality in the free- ware version of the VTEX compiler, as available on CTAN sites in systems/vtex.
# GEX is a graphics counterpart to TEX. .. Since GEX may exercise subtle influence on TEX (load fonts, or change TEX registers), GEX is op- tional in VTEX implementations: the default oper- ation of the program is with GEX off; it is enabled by a command-line switch.
# \includegraphics[width=1.3in, colorspace=grayscale 256]{macaw.jpg}
# http://mail.tug.org/texlive/Contents/live/texmf-dist/doc/generic/FAQ-en/html/FAQ-TeXsystems.html
# A free version of the commercial VTeX extended TeX system is available for use under Linux, which among other things specialises in direct production of PDF from (La)TeX input. Sadly, it���s no longer supported, and the ready-built images are made for use with a rather ancient Linux kernel.
# NOTE: another way to capture metadata; if converting via ghostscript:
# http://compgroups.net/comp.text.pdf/How-to-specify-metadata-using-Ghostscript
# first:
# grep -a 'Keywo' orig.pdf
# /Author(xxx)/Title(ttt)/Subject()/Creator(LaTeX)/Producer(pdfTeX-1.40.12)/Keywords(kkkk)
# then - copy this data in a file prologue.ini:
#/pdfmark where {pop} {userdict /pdfmark /cleartomark load put} ifelse
#[/Author(xxx)
#/Title(ttt)
#/Subject()
#/Creator(LaTeX with hyperref package + gs w/ prologue)
#/Producer(pdfTeX-1.40.12)
#/Keywords(kkkk)
#/DOCINFO pdfmark
#
# finally, call gs on the orig file,
# asking to process pdfmarks in prologue.ini:
# gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
# -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -dDOPDFMARKS \
# -sOutputFile=out.pdf in.pdf prologue.ini
# then the metadata will be in output too (which is stripped otherwise;
# note bookmarks are preserved, however).

答案3

我还有一些扫描的彩色 pdf 和灰度 pdf，我想将其转换为黑白。我尝试gs与此处列出的代码，图像质量良好，pdf 文本仍然存在。但是，该 gs 代码仅转换为灰度（如问题中所要求的）并且文件大小仍然很大。convert直接使用时效果很差。

我想要具有良好图像质量和较小文件大小的黑白 pdf。我本想尝试 terdon 的解决方案，但我无法pdftk使用 yum 进入 centOS 7（在撰写本文时）。

我的解决方案用于gs从pdf中提取灰度bmp文件，convert将这些bmp阈值设置为bw并将它们保存为tiff文件，然后图像2pdf压缩 tiff 图像并将它们全部合并到一个 pdf 中。

我尝试直接从 pdf 转到 tiff，但质量不一样，所以我将每个页面保存为 bmp。对于一页 pdf 文件，convert从 bmp 到 pdf 的效果非常好。例子：

gs -sDEVICE=bmpgray -dNOPAUSE -dBATCH -r300x300 \
   -sOutputFile=./pdf_image.bmp ./input.pdf

convert ./pdf_image.bmp -threshold 40% -compress zip ./bw_out.pdf

对于多页，gs可以将多个 pdf 文件合并为一个，但img2pdf生成的文件大小比 gs 小。 tiff 文件必须解压缩作为 img2pdf 的输入。请记住，对于大量页面，中间 bmp 和 tiff 文件的大小往往很大。pdftk或者joinpdf如果他们可以合并压缩的 pdf 文件，那就更好了convert。

我想有一个更优雅的解决方案。然而，我的方法产生的结果具有非常好的图像质量和更小的文件大小。要将文本恢复到黑白 pdf 中，请再次运行 OCR。

我的 shell 脚本使用 gs、convert 和 img2pdf。根据需要更改开头列出的参数（页数、扫描 dpi、阈值 % 等），然后运行chmod +x ./pdf2bw.sh。这是完整的脚本（pdf2bw.sh）：

#!/bin/bash

num_pages=12
dpi_res=300
input_pdf_name=color_or_grayscale.pdf
bw_threshold=40%
output_pdf_name=out_bw.pdf
#-------------------------------------------------------------------------
gs -sDEVICE=bmpgray -dNOPAUSE -dBATCH -q -r$dpi_res \
   -sOutputFile=./%d.bmp ./$input_pdf_name
#-------------------------------------------------------------------------
for file_num in `seq 1 $num_pages`
do
  convert ./$file_num.bmp -threshold $bw_threshold \
          ./$file_num.tif
done
#-------------------------------------------------------------------------
input_files=""

for file_num in `seq 1 $num_pages`
do
  input_files+="./$file_num.tif "
done

img2pdf -o ./$output_pdf_name --dpi $dpi_res $input_files
#-------------------------------------------------------------------------
# clean up bmp and tif files used in conversion

for file_num in `seq 1 $num_pages`
do
  rm ./$file_num.bmp
  rm ./$file_num.tif
done

答案4

RHEL6 和 RHEL5（两者都以 8.70 为 Ghostscript 的基线）无法使用上面给出的命令的形式。假设脚本或函数期望 PDF 文件作为第一个参数“$1”，则以下内容应该更可移植：

gs \
    -sOutputFile="grey_$1" \
    -sDEVICE=pdfwrite \
    -sColorConversionStrategy=Mono \
    -sColorConversionStrategyForImages=/Mono \
    -dProcessColorModel=/DeviceGray \
    -dCompatibilityLevel=1.3 \
    -dNOPAUSE -dBATCH \
    "$1"

输出文件将以“grey_”为前缀。

RHEL6和5都可以使用兼容性级别=1.4这要快得多，但我的目标是便携性。

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