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https://github.com/maxim/skeptick

Better ImageMagick for Ruby
https://github.com/maxim/skeptick

image-processing imagemagick ruby

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Better ImageMagick for Ruby

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# Skeptick: Better ImageMagick for Ruby



[![Build Status](https://travis-ci.org/maxim/skeptick.png?branch=master)](https://travis-ci.org/maxim/skeptick)

[![Code Climate](https://codeclimate.com/github/maxim/skeptick.png)](https://codeclimate.com/github/maxim/skeptick)

[![Dependency Status](https://gemnasium.com/maxim/skeptick.png)](https://gemnasium.com/maxim/skeptick)



Skeptick is an all-purpose DSL for building and running ImageMagick commands.

It helps you build any transformations, from trivial resizes to complex mask

algorithms and free drawing. In a nutshell, Skeptick is nothing more than a

string manipulator and a process spawner. That's all it's meant to be. However,

with Skeptick you get quite a few advantages over using plain shell-out or other

libraries.



## What you get



* Clean Ruby syntax to build ImageMagick commands

* Composable Image objects

* ImageMagick's `STDERR` output revealed in a Ruby exception

* Ability to save intermediate images for debugging

* Minimal memory consumption on shell-outs thanks to

[posix-spawn](https://github.com/rtomayko/posix-spawn)

* Emphasis on performing the whole transformation in a single command



## Installation



Add this line to your application's Gemfile:



    gem 'skeptick'



And then execute:



    $ bundle



Or install it yourself as:



    $ gem install skeptick



## Usage



To use Skeptick, you simply require it and include the module into your class.



```ruby

require 'skeptick'



class MyClass

  include Skeptick



  def convert_some_image

    cmd = convert(to: 'result.png') do

      # ...

    end



    cmd.run

  end

end

```



The `cmd` object seen in above example can be inspected to see the exact command

that Skeptick will run. Simply use `cmd.inspect` or `cmd.to_s`. Skeptick never

runs anything until you call `run` (except for one very special case), so you

can inspect commands all you want before executing them.



If you don't want to require all of Skeptick, you can just require the core, and

and select any specific sugar you want.



```ruby

require 'skeptick/core'

require 'skeptick/sugar/resized_image'

require 'skeptick/sugar/compose'

```



See the `lib/skeptick/sugar` dir for all the goodies.



In Rails Skeptick will automatically use `Rails.logger` and `Rails.root` as

`cd_path`. You can also configure your own.



```ruby

Skeptick.logger  = MyLogger.new

Skeptick.cd_path = '/some/dir'

```



You can enable `debug_mode` to display every executed command in the log.



```ruby

Skeptick.debug_mode = true

```



## Security Note



*Never* insert any user input into any of Skeptick's commands. This should be

obvious. Skeptick executes strings in your shell.



## DSL



![Skeptick Logo](https://raw.github.com/maxim/skeptick/master/logo.png)



Take a look at [logo.rb](logo.rb) to see thow this logo was generated.



A lot is going on in the above script, no worries, it's just a showcase. I bet

the first thing you noticed is a shitstorm of little method names like `canvas`,

`font`, `write`, `draw`, etc. Well, they are all sugar. We will cover sugar

below.



There are actually only 2 useful methods in all of Skeptick: `convert` and

`set`.



### Convert



`convert` can be used both standalone and inside another `convert`. You could

say this.



```ruby

command = convert('image1.png', to: 'image2.png') do

  set :resize, '200x200'

end



# OUTPUT:

# convert image1.png -resize 200x200 image2.png

```



Or you could put it inside, and it will become a parenthesized subcommand.



```ruby

command = convert('image1.png', to: 'image2.png') do

  convert do

    set '+clone'           # pull in image1 into parentheses

    set :resize, '100x100' # resize image1's clone in memory

  end



  set '-compose', 'over'

  set '-composite'

end



# OUTPUT:

# convert image1.png ( +clone -resize 100x100 )

#   -compose over -composite image2.png

```



If you love parentheses a lot, you could nest `convert` infinitely. However,

ImageMagick's `clone`, `delete`, and `swap` are your friends, learn them to

cure parenthethitis.



Oh, speaking of nesting — we can reuse that whole command inside another command

by passing it to `convert` in place of an image filepath.



```ruby

new_command = convert(command, to: 'whatever.png') do

  set '-resize', '300x300'

end



# OUTPUT:

# convert

#   ( image1.png ( +clone -resize 100x100 ) -compose over -composite )

#   -resize 300x300 whatever.png

```



See what I did there? The `command` from previous snippet is passed into

`convert`. If you have a `convert` object in a variable, you can use it inside

another `convert` object down the line. Nesting possibilities are endless.



The same snippet could also be written like this.

```ruby

new_command = convert(to: 'whatever.png') do

  image command

  set :resize, '300x300'

end

```



2 differences: 1 - instead of passing in `command` as argument we declare it

inside the block. 2 - resize is a symbol. Any symbol passed into `set`

automatically becomes a string with dash in front of it. Speaking of set.



### Set



`set` adds stuff to your command. You can give it any various arguments, it

doesn't care.



```ruby

# Works the same way:

set '-resize', '100x100'

set :resize, '100x100'



# bad, won't work

set '-resize 100x100'

```



Watch out for the fact that it shell-escapes every argument, so if you write `set '-resize foo'`, you will get an error, since the space will be escaped, and shell would treat that whole string as single word.`



In addition to `set` there are also `prepend` and `append` to put stuff at the

beginning or end of a command, but they are rarely useful, and mostly for

implementing your own sugar.



## Sugar



Skeptick comes with a bunch of sugar. When you require Skeptick, you can simply

require everything. This includes all the sugar functionality.



```ruby

require 'skeptick'

```



However, you can require just the core stuff described above, and select any

sugar you want.



```ruby

require 'skeptick/core'

require 'skeptick/sugar/compose'

```



### Compose Sugar



Compose is sugar that adds `compose` shortcut to Skeptick's DSL.



```ruby

command = compose(:multiply, 'a.png', 'b.png', to: 'out.png') do

  set :resize, '200x200'

end



# OUTPUT:

# convert a.png b.png -compose multiply -resize 200x200 -composite out.png

```



It takes the blending type as the first argument, and injects some extra stuff

into the resulting command.



As with `convert`, you don't have to list your images as method arguments.

Instead you could declare them inside the block using the `image` method. The

following command does the same thing.



```ruby

command = compose(:multiply, to: 'out.png') do

  image 'a.png'

  convert 'b.png'

  set :resize, '200x200'

end

```



*Note:* `image` is alias of `convert`.



Since most of Skeptick's power comes from the ability to infinitely nest things,

here's an example involving a nested `compose`.



```ruby

command = convert('image1.png', to: 'result.png') do

  compose(:multiply) do

    image 'image2.png[200x200]'



    convert 'image3.png' do

      set :unsharp, '0x5'

    end

  end

end



# OUTPUT:

# convert

#   image1.png image2.png[200x200] ( image3.png -unsharp 0x5 ) -compose

#   multiply -composite result.png"

```



Notice how we nest `compose` inside of `convert`, and then `convert` inside of

`compose`.



### Compose Operators



This is more of a gimmick than a real feature, but you can use math operators

like `+`, `-`, `*`, `/`, `&`, `|` to compose images. These are all based on

`compose` method. Here's a multiply example.



```ruby

image1 = image('foo.png')

image2 = image('bar.png')

result = convert(image1 * image2, to: 'baz.png')



# OUTPUT:

# convert foo.png bar.png -compose multiply -composite baz.png

```



As you can see, this is equivalent of simply using `compose`.



```ruby

# Same thing

result = compose(:multiply, 'foo.png', 'bar.png', to: 'baz.png')

```



Check out [lib/skeptick/sugar/compose.rb](lib/skeptick/sugar/compose.rb) for

what these operators do.



### clone, delete, swap



Skeptick provides methods `clone`, `delete`, and `swap` to

manipulate declared images in a sequence, just like in ImageMagick CLI.



```ruby

command = compose(:over, 'image1.png', to: 'result.png') do

  # You could think of image sequence as a ruby array. Here's what it would

  # look like right now.

  # [ 'image1.png' ]



  compose(:multiply) do

    image 'mask.png' # loading another image for this operation

    clone(0)         # cloning image1.png from outside "into parentheses"

  end



  # Sequence at this point:

  # [ 'image1.png', 'result of compose(:multiply)' ]



  delete(0) # deleting image1.png from the sequence and from memory



  # Sequence at this point:

  # [ 'result of compose(:multiply)' ]



  # At this point the only image loaded in memory is the one produced by the

  # compose(:multiply) command above. Let's load another one.



  image 'image2.png'



  # Sequence at this point:

  # [ 'result of compose(:multiply)', 'image2.png' ]



  # Now we have two images in the sequence. We can swap them in case we need

  # to change their order.



  swap



  # Sequence at this point:

  # [ 'image2.png', 'result of compose(:multiply)' ]



  # Now image2.png is first in the sequence, and the output of

  # compose(:multiply) is second. Since our outermost command is compose(:over),

  # at this point these 2 images will be composed over each other, and the

  # result written to result.png.

end



# OUTPUT

# convert

#  image1.png ( mask.png -clone 0 -compose multiply -composite )

#  -delete 0 image2.png +swap -compose over -composite result.png

```



You can use `clone` and `delete` to refer to multiple images at once by passing

mutliple indexes as arguments, like `clone(0,1,2)` or `delete(0,1)`. Ranges are

also accepted. Without any arguments `clone` and `delete` are translated to

ImageMagick's `+clone` and `+delete`. They then refer to the last image in the

sequence. Same with `swap` - you can provide two indexes in arguments like

`swap(1,3)` to swap any 2 images in the sequence, or without arguments it'll

act as `+swap` - which swaps last two images.



### Write



Sometimes you might want to take a look at an intermediate image that's being

generated inside parentheses, nested somewhere in your command. You can do so

with the help of `write '/path/to/img.png'`, which is defined in

`skeptick/sugar/write.rb`.



```ruby

command = convert(to: 'result.png') do

  compose(:multiply, 'a.png', 'b.png') do

    write '~/Desktop/debug.png'

  end



  set :resize, '200x200'

end

```



In this case the result of inner `compose` command will be saved to desktop

without affecting anything else. This is a feature that already exists in

ImageMagick, as you can see for yourself from generated command:



    convert

      ( a.png b.png -compose multiply -composite -write ~/Desktop/debug.png )

      -resize 200x200 result.png



Documentation is to be continued...



## Contributing



1. Fork it

2. Create your feature branch (`git checkout -b my-new-feature`)

3. Commit your changes (`git commit -am 'Add some feature'`)

4. Push to the branch (`git push origin my-new-feature`)

5. Create new Pull Request