imagemagick:修改图片的dpi(分辨率/Resolution)(ImageMagick 6.9.10)

一，如何查看图片的dpi?

[lhdop@blog test3]$ identify -verbose 8.jpg
Image: 8.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Mime type: image/jpeg
  Class: DirectClass
  Geometry: 1333x1867+0+0
  Resolution: 150x150
  Print size: 8.88667x12.4467
  Units: PixelsPerInch
  Colorspace: sRGB
  Type: TrueColor
  Base type: Undefined
  Endianess: Undefined
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
  Channel statistics:
    Pixels: 2488711
    Red:
      min: 0  (0)
      max: 255 (1)
      mean: 172.019 (0.674585)
      standard deviation: 61.9397 (0.242901)
      kurtosis: -0.690127
      skewness: -0.678042
      entropy: 0.912948
    Green:
      min: 0  (0)
      max: 255 (1)
      mean: 137.225 (0.538138)
      standard deviation: 66.6771 (0.261479)
      kurtosis: -1.17921
      skewness: -0.0919349
      entropy: 0.923473
    Blue:
      min: 0  (0)
      max: 255 (1)
      mean: 93.0464 (0.364888)
      standard deviation: 74.6528 (0.292756)
      kurtosis: -1.29616
      skewness: 0.574976
      entropy: 0.879247
  Image statistics:
    Overall:
      min: 0  (0)
      max: 255 (1)
      mean: 134.097 (0.52587)
      standard deviation: 67.7565 (0.265712)
      kurtosis: -1.40475
      skewness: -0.134471
      entropy: 0.905222
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgb(223,223,223)
  Matte color: grey74
  Transparent color: black
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 1333x1867+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: JPEG
  Quality: 92
  Orientation: Undefined
  Profiles:
    Profile-8bim: 28 bytes
    Profile-icc: 3144 bytes
  Properties:
    date:create: 2022-04-26T00:42:59+00:00
    date:modify: 2020-08-18T03:12:51+00:00
    icc:copyright: Copyright (c) 1998 Hewlett-Packard Company
    icc:description: sRGB IEC61966-2.1
    icc:manufacturer: IEC http://www.iec.ch
    icc:model: IEC 61966-2.1 Default RGB colour space - sRGB
    jpeg:colorspace: 2
    jpeg:sampling-factor: 1x1,1x1,1x1
    signature: cc865a4d4f34d8ebe21978885849dfe3d98f06b501fe140c8f265f0344a891a4
  Artifacts:
    filename: 8.jpg
    verbose: true
  Tainted: False
  Filesize: 1.13321MiB
  Number pixels: 2.48871M
  Pixels per second: 65.5681MB
  User time: 0.030u
  Elapsed time: 0:01.037
  Version: ImageMagick 6.9.10-86 Q16 x86_64 2020-01-13 https://imagemagick.org

可以看到dpi：

Resolution: 150x150

两个150分别是水平和垂直方向的分辨率

 

只查看图片的宽高:

[lhdop@blog test3]$ identify 8.jpg
8.jpg JPEG 1333x1867 1333x1867+0+0 8-bit sRGB 1.13321MiB 0.000u 0:00.000

也可以用软件查看，例如 XnViewMp:

说明：刘宏缔的架构森林是一个专注架构的博客，

网站：https://blog.imgtouch.com
本文: https://blog.imgtouch.com/index.php/2023/06/01/imagemagick-xiu-gai-tu-pian-de-dpi-fen-bian-lyu-resolution/

         对应的源码可以访问这里获取： https://github.com/liuhongdi/
         或: https://gitee.com/liuhongdi

说明：作者:刘宏缔 邮箱: 371125307@qq.com

二，用convert修改dpi

1,从命令行修改

[lhdop@blog test3]$ convert 8.jpg -density 300 8_300.jpg

2,修改后查看dpi:

[lhdop@blog test3]$ identify -verbose 8_300.jpg
Image: 8_300.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Mime type: image/jpeg
  Class: DirectClass
  Geometry: 1333x1867+0+0
  Resolution: 300x300
  Print size: 4.44333x6.22333
  Units: PixelsPerInch
  Colorspace: sRGB
  Type: TrueColor
  Base type: Undefined
  Endianess: Undefined
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
  Channel statistics:
    Pixels: 2488711
    Red:
      min: 0  (0)
      max: 255 (1)
      mean: 172.02 (0.674589)
      standard deviation: 61.9966 (0.243124)
      kurtosis: -0.685443
      skewness: -0.680275
      entropy: 0.913934
    Green:
      min: 0  (0)
      max: 255 (1)
      mean: 137.224 (0.538135)
      standard deviation: 66.7195 (0.261645)
      kurtosis: -1.17922
      skewness: -0.0924288
      entropy: 0.924804
    Blue:
      min: 0  (0)
      max: 255 (1)
      mean: 93.053 (0.364914)
      standard deviation: 74.6826 (0.292873)
      kurtosis: -1.29582
      skewness: 0.575793
      entropy: 0.8809
  Image statistics:
    Overall:
      min: 0  (0)
      max: 255 (1)
      mean: 134.099 (0.525879)
      standard deviation: 67.7996 (0.265881)
      kurtosis: -1.40557
      skewness: -0.134436
      entropy: 0.906546
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgb(223,223,223)
  Matte color: grey74
  Transparent color: black
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 1333x1867+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: JPEG
  Quality: 92
  Orientation: Undefined
  Profiles:
    Profile-8bim: 28 bytes
    Profile-icc: 3144 bytes
  Properties:
    date:create: 2022-06-04T08:01:33+00:00
    date:modify: 2022-06-04T08:01:33+00:00
    icc:copyright: Copyright (c) 1998 Hewlett-Packard Company
    icc:description: sRGB IEC61966-2.1
    icc:manufacturer: IEC http://www.iec.ch
    icc:model: IEC 61966-2.1 Default RGB colour space - sRGB
    jpeg:colorspace: 2
    jpeg:sampling-factor: 1x1,1x1,1x1
    signature: 26f0ecbbec90899865350b3e9ab5dc84b621cf047a0465ce5c06da8d85ffb06d
  Artifacts:
    filename: 8_300.jpg
    verbose: true
  Tainted: False
  Filesize: 1.253MiB
  Number pixels: 2.48871M
  Pixels per second: 65.669MB
  User time: 0.030u
  Elapsed time: 0:01.037
  Version: ImageMagick 6.9.10-86 Q16 x86_64 2020-01-13 https://imagemagick.org

可以看到:dpi已变为:

Resolution: 300x300

在本地用xnviewmp查看:

可以看到图片的dpi已修改为 300x300

 

总结:修改图片dpi后，图片的长宽没有变，

可以看到图片的打印尺寸发生了变化：

相同的长宽像素时，更高的DPI表现为物理尺寸更小 - 这个很好理解，同样多的像素点，由于DPI高，所以需要的物理尺寸更少

以上图为例:

高度为 1867, 1867/300 = 6.22英寸

1867/150 = 12.45英寸,

所以dpi越高，则打印尺寸越小

三，查看imagemagick的版本:

[lhdop@blog ~]$ identify -version
Version: ImageMagick 6.9.10-86 Q16 x86_64 2020-01-13 https://imagemagick.org
Copyright: © 1999-2020 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP(4.5)
Delegates (built-in): bzlib cairo fftw fontconfig freetype gslib gvc jbig jng jp2 
jpeg lcms ltdl lzma openexr pangocairo png ps raqm raw rsvg tiff webp wmf x xml zlib