linux 修改图片的尺寸

# convert -sample 500x500! 512.png 500.png #把512*512的图片修改为500*500的图片
# which convert
/usr/bin/convert
# rpm -qf /usr/bin/convert 
ImageMagick-6.7.8.9-15.el7_2.x86_64
# yum search ImageMagick
Loaded plugins: fastestmirror, langpacks
Determining fastest mirrors
 * base: mirrors.tuna.tsinghua.edu.cn
 * epel: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirror.vodien.com
=========================== N/S matched: ImageMagick ===========================
ImageMagick-c++.i686 : ImageMagick Magick++ library (C++ bindings)
ImageMagick-c++.x86_64 : ImageMagick Magick++ library (C++ bindings)
ImageMagick-c++-devel.i686 : C++ bindings for the ImageMagick library
ImageMagick-c++-devel.x86_64 : C++ bindings for the ImageMagick library
ImageMagick-devel.i686 : Library links and header files for ImageMagick app
                       : development
ImageMagick-devel.x86_64 : Library links and header files for ImageMagick app
                         : development
ImageMagick-doc.x86_64 : ImageMagick html documentation
ImageMagick-perl.x86_64 : ImageMagick perl bindings
GraphicsMagick.i686 : An ImageMagick fork, offering faster image generation and
                    : better quality
GraphicsMagick.x86_64 : An ImageMagick fork, offering faster image generation
                      : and better quality
ImageMagick.i686 : An X application for displaying and manipulating images
ImageMagick.x86_64 : An X application for displaying and manipulating images
php-magickwand.x86_64 : PHP API for ImageMagick
php-pecl-imagick.x86_64 : Provides a wrapper to the ImageMagick library

  Name and summary matches only, use "search all" for everything.