Add support for custom GraphicsMagick output arguments (e.g. sharpen)

This will help support thumbsup/thumbsup#89

README.md

@@ -71,6 +71,14 @@ opts = {
     tile: false
   }
 }
+
+// custom post-processing using GraphicsMagick output arguments
+options = {
+  args: [
+    '-unsharp 2 0.5 0.7 0',
+    '-modulate 120'
+  ]
+}
 ```
 
 Note: watermarks are not compatible with cropped images.

lib/gmargs.js

@@ -0,0 +1,18 @@
+/*
+  Applies an array of GraphicsMagick string arguments to a <gm> instance
+  e.g. apply(image, ['--modulate 120'])
+*/
+exports.apply = function (image, args) {
+  if (args && args.length) {
+    args.forEach(arg => {
+      const index = arg.indexOf(' ')
+      if (index === -1) {
+        image.out(arg)
+      } else {
+        const command = arg.substr(0, index)
+        const values = arg.substr(index + 1)
+        image.out(command, values)
+      }
+    })
+  }
+}

lib/index.js

@@ -2,6 +2,7 @@ const async = require('async')
 const gm = require('gm')
 const mkdirp = require('mkdirp')
 const path = require('path')
+const gmargs = require('./gmargs')
 const ffmpeg = require('./ffmpeg')
 
 /*
@@ -41,6 +42,8 @@ exports.image = function (source, target, options, callback) {
   }
   // default quality, for typical web-friendly sizes
   image.quality(options.quality || 90)
+  // apply custom post-processing arguments (sharpen, brightness...)
+  gmargs.apply(image, options.args)
   // write the output image
   image.write(target, callback)
 }

test/gmargs.js

@@ -0,0 +1,69 @@
+const gmargs = require('../lib/gmargs')
+const sinon = require('sinon')
+const tape = require('tape')
+
+function gm () {
+  return {
+    out: sinon.stub()
+  }
+}
+
+tape('no arguments', t => {
+  t.plan(1)
+  const image = gm()
+  gmargs.apply(image, undefined)
+  t.equal(image.out.callCount, 0)
+  t.end()
+})
+
+tape('empty array of arguments', t => {
+  t.plan(1)
+  const image = gm()
+  gmargs.apply(image, [])
+  t.equal(image.out.callCount, 0)
+  t.end()
+})
+
+tape('single argument with no values', t => {
+  t.plan(2)
+  const image = gm()
+  gmargs.apply(image, ['-equalize'])
+  t.equal(image.out.callCount, 1)
+  t.deepEqual(image.out.args[0], ['-equalize'])
+  t.end()
+})
+
+tape('single argument with one value', t => {
+  t.plan(2)
+  const image = gm()
+  gmargs.apply(image, ['-modulate 120'])
+  t.equal(image.out.callCount, 1)
+  t.deepEqual(image.out.args[0], ['-modulate', '120'])
+  t.end()
+})
+
+tape('single argument with space-separated values', t => {
+  t.plan(2)
+  const image = gm()
+  gmargs.apply(image, ['-unsharp 2 0.5 0.5 0'])
+  t.equal(image.out.callCount, 1)
+  t.deepEqual(image.out.args[0], ['-unsharp', '2 0.5 0.5 0'])
+  t.end()
+})
+
+tape('multiple arguments', t => {
+  t.plan(2)
+  const image = gm()
+  gmargs.apply(image, [
+    '-equalize',
+    '-modulate 120',
+    '-unsharp 2 0.5 0.5 0'
+  ])
+  t.equal(image.out.callCount, 3)
+  t.deepEqual(image.out.args, [
+    ['-equalize'],
+    ['-modulate', '120'],
+    ['-unsharp', '2 0.5 0.5 0']
+  ])
+  t.end()
+})

test/image.js

@@ -140,6 +140,16 @@ tape('ignores the watermark when cropping', (test) => {
   })
 })
 
+tape('can add custom post-processing arguments', (test) => {
+  diff.image(test, {
+    input: 'images/desk.jpg',
+    expect: 'images/desk.processed.jpg',
+    options: {
+      args: ['-equalize', '-modulate 120']
+    }
+  })
+})
+
 const ORIENTATIONS = [1, 2, 3, 4, 5, 6, 7, 8]
 
 ORIENTATIONS.forEach((orientation) => {