ImageMagick: Convert & Edit Image via Command Line

ImageMagick is a free software that lets you create/edit/convert images via command line. You can download and install ImageMagick for Linux, Windows, and Mac Operating System.

ImageMagick provides a lot of features that you can apply to an image like:

– get detailed image information
– resize, crop image
– flip and rotate image
– blur, sharpen, distort image
– adjust image colors
– draw text, line, and different shapes in image
– overlap one image into another
– add border or frame to an image
– convert an image from one format to another (e.g. PNG to JPEG)
– has support for large size images (mega, giga, tera pixel image size)
– recognize patterns and shapes in image

The basic style of the command of ImageMagick is as follows:

command [options] image1 [options] image2 [options] output_image

The ImageMagick site has lots of good examples of commands to perform various image operations. I will be listing some of the basic examples of the commands over here.

Get Image Information

We can use ImageMagick’s identify program to get the detailed information about any image.

It can:

– describe the format and characteristics of one or more image files
– report if an image is incomplete or corrupt
– get width and height of an image
– check if the image is colormapped or not
– get the number of byets in the image
– get the format of the image (JPEG, PNG, etc.)
– get the number of seconds that ImageMagick took to read and process the image
– get more detailed information using the -verbose option

The identify program can also be used to get the installed version number of ImageMagick itself by running the following command:

magick identify --version

The output will be something like this:

Version: ImageMagick 7.0.7-23 Q16 x86_64 2018-02-19 http://www.imagemagick.org
Copyright: © 1999-2018 ImageMagick Studio LLC
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC HDRI Modules
Delegates (built-in): bzlib freetype jng jpeg ltdl lzma png tiff xml zlib

Get information of an image

magick identify shadow.png

Output will be something like this:

shadow.png PNG 82x58 82x58+0+0 8-bit sRGB 8702B 0.000u 0:00.000

Get verbose information of an image

Get the detailed information of the same image:

magick identify -verbose shadow.png

Output will be something like this:

Image: shadow.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 82x58+0+0
  Units: Undefined
  Colorspace: sRGB
  Type: TrueColorAlpha
  Base type: Undefined
  Endianess: Undefined
  Depth: 8-bit
  Channel depth:
    Red: 8-bit
    Green: 8-bit
    Blue: 8-bit
    Alpha: 8-bit
  Channel statistics:
    Pixels: 4756
    Red:
      min: 0  (0)
      max: 255 (1)
      mean: 98.6529 (0.386874)
      standard deviation: 88.8551 (0.348451)
      kurtosis: -1.25895
      skewness: 0.359817
      entropy: 0.770452
    Green:
      min: 0  (0)
      max: 255 (1)
      mean: 60.4327 (0.236991)
      standard deviation: 60.0569 (0.235517)
      kurtosis: 1.88261
      skewness: 1.31123
      entropy: 0.700643
    Blue:
      min: 24  (0.0941176)
      max: 255 (1)
      mean: 95.8192 (0.375761)
      standard deviation: 50.5063 (0.198064)
      kurtosis: 1.16538
      skewness: 1.07072
      entropy: 0.69015
    Alpha:
      min: 0  (0)
      max: 255 (1)
      mean: 196.743 (0.771542)
      standard deviation: 92.1225 (0.361265)
      kurtosis: -0.347426
      skewness: -1.1676
      entropy: 0.406634
  Image statistics:
    Overall:
      min: 0  (0)
      max: 255 (1)
      mean: 112.912 (0.442792)
      standard deviation: 72.8852 (0.285824)
      kurtosis: -1.18265
      skewness: 0.436057
      entropy: 0.641969
  Alpha: srgba(0,0,128,0)   #00008000
  Rendering intent: Perceptual
  Gamma: 0.45455
  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)
  Matte color: grey74
  Background color: black
  Border color: srgb(223,223,223)
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 82x58+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    date:create: 2018-08-12T16:24:30+06:00
    date:modify: 2018-08-12T16:24:20+06:00
    png:bKGD: chunk was found (see Background color, above)
    png:cHRM: chunk was found (see Chromaticity, above)
    png:gAMA: gamma=0.45454544 (See Gamma, above)
    png:IHDR.bit-depth-orig: 8
    png:IHDR.bit_depth: 8
    png:IHDR.color-type-orig: 6
    png:IHDR.color_type: 6 (RGBA)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 82, 58
    png:sRGB: intent=0 (Perceptual Intent)
    png:text: 2 tEXt/zTXt/iTXt chunks were found
    png:tIME: 2018-08-12T22:24:20Z
    signature: 817abb638e17f28c5ab4549ee9e1328850f1dfb9f23058ddb2150b809ea3ccb3
  Artifacts:
    verbose: true
  Tainted: False
  Filesize: 8702B
  Number pixels: 4756
  Pixels per second: 475600B
  User time: 0.000u
  Elapsed time: 0:01.009
  Version: ImageMagick 7.0.7-23 Q16 x86_64 2018-02-19 http://www.imagemagick.org

Convert an image from one format to another

Here, we convert the image from PNG to JPEG format:

convert shadow.png shadow.jpeg

Resize and convert to another format:

convert shadow.jpeg -resize 50% shadow1.png

Resize Image

Resize image to 100×100 pixels by maintaining the aspect ratio

Suppose, if your input image is 800×600 pixels then the resized output image will be 100×75 pixels in size.

convert input.png -resize 100x100 output.png

Resize image to 100×100 pixels ignoring aspect ration

• the image will be resized exactly into 100×100 pixels

convert input.png -resize 100x100\! output.png

Only resize image that is larger than the resize size

• if we provide 200×200 pixel size image, then it will be resized to 100×100 px
• if we provide 50×50 pix image then it will not resize and remain as it is
• So, this is kind of Image Shrinking feature

convert input.png -resize 100x100\> output.png

Only resize image that is smaller than the resize size

• if we provide 200×200 pixel size image, then it will be resized to 100×100 px
• if we provide 50×50 pix image then it will not resize and remain as it is
• So, this is kind of Image Enlarging feature only

convert input.png -resize 100x100\< output.png

Resize image to percentage size by maintaining the aspect ratio

The following command will resize the image into half of its size.

Suppose, if your input image is 800×600 pixels then the resized output image will be 400×300 pixels in size.

convert input.png -resize 50% output.png

Rotate Image

Rotate image 90 degree clockwise

convert input.png -rotate "90" output.png

Rotate image 45 degree anti-clockwise/counter-clockwise

convert input.png -rotate "-45" output.png

Blur Image

Blur arguments are:

-blur  {radius}x{sigma} 

radius:
– how big an area the operator should look at when spreading pixels
– can be either ‘0’ or at a minimum double that of the sigma value

sigma:
– how much your want the image to ‘spread’ or blur, in pixels
– it’s kind of the size of the brush used to blur the image
– it can have floating point value

convert input.png -blur 0x8 output.png

Sharpen Image

Sharpen arguments are:

-blur  {radius}x{sigma} 

radius:
– can have integer value only
– should be at a minimum 1 or double of the sigma value

sigma:
– it is the real control of the sharpening operation
– it can have floating point value starting from .1
– the larger the sigma, the more it sharpens
– practically, no more than sigma value 3 for server sharpening
– 0.5 to 1 is a good range

convert input.png -sharpen 0x3 output.png

Encrypt and Decrypt an Image

You can scramble the entire image and make it unrecognizable by using the enciphering utility in ImageMagick.

-encipher option is used to scramble/encrypt the image

We will use a passphrase.txt file to scramble the image. The file that is used to scramble the image is required to unscramble the image as well.

Let’s first run a command to create a file named passphrase.txt:

touch passphrase.txt

Scramble the image

convert shadow.jpeg -encipher passphrase.txt shadow-encrypted.jpeg

Unscramble the image

-decipher option is used to unscramble/decrypt the image

convert shadow-encrypted.jpeg -decipher passphrase.txt shadow-decrypted.jpeg

We can also use image file instead of the .txt file to scramble and unscramble any image:

convert shadow.jpeg -encipher my-image.png shadow-encrypted.jpeg

convert shadow-encrypted.jpeg -decipher my-image.png shadow-decrypted.jpeg

Remember that the image named my-image.png should be present in order to scramble and unscramble the image.

Overlap one image over another image

The composite program is used to overlay one image over another.

composite -gravity center smile.gif  rose: rose-over.png

Convert Text into Image

convert -background lightyellow -fill brown  -font TimesNewRoman \
          -size 165x70  -pointsize 24  -gravity center \
          label:Mukesh     label_name.gif

Add multiple words text. But, if the text is long and the size of the image is small then the text will overflow from the image.

convert -background lightyellow -fill brown  -font TimesNewRoman \
          -size 200x100  -pointsize 24  -gravity center \
          label:'My name is Mukesh Chapagain'     label_name.gif

In that case, we can use caption instead of label. This will WordWrap the long text.

convert -background lightyellow -fill brown  -font TimesNewRoman \
          -size 200x100  -pointsize 24  -gravity center \
          caption:'My name is Mukesh Chapagain'     label_name.gif

You can use caption for multiple line words as well. It detects the \n character as new line.

convert -background lightyellow -fill brown  -font TimesNewRoman \
          -size 200x100  -pointsize 24  -gravity center \
          caption:'My name is \n Mukesh Chapagain'     label_name.gif

Draw Shapes in an Image

Using the -draw option in ImageMagick, we can draw various shapes like line, rectangle, circle, etc.

Create an Image and Draw a Point in it

convert -size 10x6 xc:skyblue  -fill black \
          -draw 'point 3,2'  -scale 100x60   draw_point.gif

Create an Image and Draw a Rectangle in it

convert -size 100x60 xc:skyblue -fill white -stroke black \
          -draw "rectangle 20,10 80,50"       draw_rect.gif

convert -size 100x60 xc:skyblue -fill white -stroke black \
          -draw "roundrectangle 20,10 80,50 20,15"  draw_rrect.gif

Create an Image and Draw a Line in it

convert -size 100x60 xc:skyblue -fill white -stroke black \
          -draw "line   20,50 90,10"    draw_line.gif

Draw a line over an Image

The following command will draw a line over an already existing image.

convert rose:  -fill none -stroke white -draw 'line 5,40 65,5'  rose_raw.png

Hope this helps. Thanks.