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在文章《使用TinyPNG来优化您的网站图片》介绍过TinyPNG提供的压缩服务，效果非常棒。ImgURL 图床也是使用TinyPNG来提供图片压缩，不过TinyPNG有免费次数限制。于是xiaoz寻找了Linux系统下的其它图片压缩方案，希望后期能够用到。

OptiPNG

OptiPNG是一种PNG优化器，可将图像文件重新压缩为更小的尺寸，而不会丢失任何信息。同时还可以压缩.bmp .gif等格式，安装方法如下：

#请先确保已经安装epel源，然后直接yum安装
yum -y install optipng
#也可以下载源码编译安装
#下载OptiPNG源码
wget -O optipng.tar.gz http://prdownloads.sourceforge.net/optipng/optipng-0.7.7.tar.gz?download
#解压
tar -zxvf optipng.tar.gz
#进入目录
cd optipng-0.7.7/
#编译安装
./configure
make && make install

如果不出意外，安装成功后可以输入optipng -V查看当前版本，如下截图。

直接输入命令optipng xxx.png来压缩一张.png的图片，optipng 还有更多的参数，可以输入optipng -h来查看帮助。

Synopsis:
    optipng [options] files ...
Files:
    Image files of type: PNG, BMP, GIF, PNM or TIFF
Basic options:
    -?, -h, -help   show this help
    -o <level>      optimization level (0-7)        [default: 2]
    -v          run in verbose mode / show copyright and version info
General options:
    -backup, -keep  keep a backup of the modified files
    -clobber        overwrite existing files
    -fix        enable error recovery
    -force      enforce writing of a new output file
    -preserve       preserve file attributes if possible
    -quiet, -silent run in quiet mode
    -simulate       run in simulation mode
    -out <file>     write output file to <file>
    -dir <directory>    write output file(s) to <directory>
    -log <file>     log messages to <file>
    --          stop option switch parsing
Optimization options:
    -f <filters>    PNG delta filters (0-5)         [default: 0,5]
    -i <type>       PNG interlace type (0-1)
    -zc <levels>    zlib compression levels (1-9)       [default: 9]
    -zm <levels>    zlib memory levels (1-9)        [default: 8]
    -zs <strategies>    zlib compression strategies (0-3)   [default: 0-3]
    -zw <size>      zlib window size (256,512,1k,2k,4k,8k,16k,32k)
    -full       produce a full report on IDAT (might reduce speed)
    -nb         no bit depth reduction
    -nc         no color type reduction
    -np         no palette reduction
    -nx         no reductions
    -nz         no IDAT recoding
Editing options:
    -snip       cut one image out of multi-image or animation files
    -strip <objects>    strip metadata objects (e.g. "all")
Optimization levels:
    -o0     <=> -o1 -nx -nz             (0 or 1 trials)
    -o1     <=> -zc9 -zm8 -zs0 -f0          (1 trial)
            (or...) -zc9 -zm8 -zs1 -f5          (1 trial)
    -o2     <=> -zc9 -zm8 -zs0-3 -f0,5          (8 trials)
    -o3     <=> -zc9 -zm8-9 -zs0-3 -f0,5        (16 trials)
    -o4     <=> -zc9 -zm8 -zs0-3 -f0-5          (24 trials)
    -o5     <=> -zc9 -zm8-9 -zs0-3 -f0-5        (48 trials)
    -o6     <=> -zc1-9 -zm8 -zs0-3 -f0-5        (120 trials)
    -o7     <=> -zc1-9 -zm8-9 -zs0-3 -f0-5      (240 trials)
    -o7 -zm1-9  <=> -zc1-9 -zm1-9 -zs0-3 -f0-5      (1080 trials)
Notes:
    The combination for -o1 is chosen heuristically.
    Exhaustive combinations such as "-o7 -zm1-9" are not generally recommended.
Examples:
    optipng file.png                        (default speed)
    optipng -o5 file.png                    (slow)
    optipng -o7 file.png                    (very slow)

OptiPNG主页：http://optipng.sourceforge.net/

jpegoptim

jpegoptim是一款开源的图片压缩工具，只能压缩.jpg格式，直接使用yum命令安装,安装完毕后可以输入jpegoptim -V查看版本。

yum -y install jpegoptim

输入命令jpegoptim -m 80 xxx.jpg来压缩图片，-m指的优化质量，可选值从0-100，数值越大速度越快、质量越好，但压缩效果更差，更多参数可以输入jpegoptim -h查看。

jpegoptim v1.4.6  Copyright (C) 1996-2018, Timo Kokkonen
Usage: jpegoptim [options] <filenames> 

  -d<path>, --dest=<path>
                    specify alternative destination directory for 
                    optimized files (default is to overwrite originals)
  -f, --force       force optimization
  -h, --help        display this help and exit
  -m<quality>, --max=<quality>
                    set maximum image quality factor (disables lossless
                    optimization mode, which is by default on)
                    Valid quality values: 0 - 100
  -n, --noaction    don't really optimize files, just print results
  -S<size>, --size=<size>
                    Try to optimize file to given size (disables lossless
                    optimization mode). Target size is specified either in
                    kilo bytes (1 - n) or as percentage (1% - 99%)
  -T<threshold>, --threshold=<threshold>
                    keep old file if the gain is below a threshold (%)
  -b, --csv         print progress info in CSV format
  -o, --overwrite   overwrite target file even if it exists (meaningful
                    only when used with -d, --dest option)
  -p, --preserve    preserve file timestamps
  -P, --preserve-perms
                    preserve original file permissions by overwriting it
  -q, --quiet       quiet mode
  -t, --totals      print totals after processing all files
  -v, --verbose     enable verbose mode (positively chatty)
  -V, --version     print program version

  -s, --strip-all   strip all markers from output file
  --strip-none      do not strip any markers
  --strip-com       strip Comment markers from output file
  --strip-exif      strip Exif markers from output file
  --strip-iptc      strip IPTC/Photoshop (APP13) markers from output file
  --strip-icc       strip ICC profile markers from output file
  --strip-xmp       strip XMP markers markers from output file

  --all-normal      force all output files to be non-progressive
  --all-progressive force all output files to be progressive
  --stdout          send output to standard output (instead of a file)
  --stdin           read input from standard input (instead of a file)

jpegoptim项目地址：https://github.com/tjko/jpegoptim

Google webp

WebP是一种现代图像格式，可为Web上的图像提供出色的无损和有损压缩。使用WebP，网站管理员和Web开发人员可以创建更小，更丰富的图像，使网络更快。

CentOS可以使用yum安装：

yum -y install libwebp-devel libwebp-tools

使用cwebp命令行上PNG或JPEG图像文件转换为WebP的格式。您可以使用以下命令将PNG图像文件转换为质量范围为80的WebP图像：

cwebp -q 80 image.png -o image.webp

更多关于webp的使用说明可以参考Google官方文档： new image format for the Web，顺带一提，国内的又拍云CDN 已经支持自动将图片转换为webp格式。

总结

无论哪种图片压缩方案都无法真正做到100%无损，只能尽可能不降低图片质量的情况下减小图片体积。建议大家对网站图片进行适当压缩，提高网站速度。如果您还有更优秀的压缩方案，请留言推荐。