Expose libvips affine operation (#2336)

docs/api-operation.md

@@ -65,6 +65,61 @@ The use of `flop` implies the removal of the EXIF `Orientation` tag, if any.
 
 Returns **Sharp** 
 
+## affine
+
+Perform an affine transform on an image. This operation will always occur after resizing, extraction and rotation, if any.
+
+You must provide an array of length 4 or a 2x2 affine transformation matrix.
+By default, new pixels are filled with a black background. You can provide a background color with the `background` option.
+A particular interpolator may also be specified. Set the `interpolator` option to an attribute of the `sharp.interpolator` Object e.g. `sharp.interpolator.nohalo`.
+
+In the case of a 2x2 matrix, the transform is:
+
+-   X = `matrix[0, 0]` \* (x + `idx`) + `matrix[0, 1]` \* (y + `idy`) + `odx`
+-   Y = `matrix[1, 0]` \* (x + `idx`) + `matrix[1, 1]` \* (y + `idy`) + `ody`
+
+where:
+
+-   x and y are the coordinates in input image.
+-   X and Y are the coordinates in output image.
+-   (0,0) is the upper left corner.
+
+### Parameters
+
+-   `matrix` **([Array][7]<[Array][7]<[number][1]>> | [Array][7]<[number][1]>)** affine transformation matrix
+-   `options` **[Object][2]?** if present, is an Object with optional attributes.
+    -   `options.background` **([String][3] \| [Object][2])** parsed by the [color][4] module to extract values for red, green, blue and alpha. (optional, default `"#000000"`)
+    -   `options.idx` **[Number][1]** input horizontal offset (optional, default `0`)
+    -   `options.idy` **[Number][1]** input vertical offset (optional, default `0`)
+    -   `options.odx` **[Number][1]** output horizontal offset (optional, default `0`)
+    -   `options.ody` **[Number][1]** output vertical offset (optional, default `0`)
+    -   `options.interpolator` **[String][3]** interpolator (optional, default `sharp.interpolators.bicubic`)
+
+### Examples
+
+```javascript
+const pipeline = sharp()
+  .affine([[1, 0.3], [0.1, 0.7]], {
+     background: 'white',
+     interpolate: sharp.interpolators.nohalo
+  })
+  .toBuffer((err, outputBuffer, info) => {
+     // outputBuffer contains the transformed image
+     // info.width and info.height contain the new dimensions
+  });
+
+inputStream
+  .pipe(pipeline);
+```
+
+-   Throws **[Error][5]** Invalid parameters
+
+Returns **Sharp** 
+
+**Meta**
+
+-   **since**: 0.27.0
+
 ## sharpen
 
 Sharpen the image.

docs/api-utility.md

@@ -12,6 +12,36 @@ console.log(sharp.format);
 
 Returns **[Object][1]** 
 
+## interpolators
+
+An Object containing the available interpolators and their proper values
+
+Type: [string][2]
+
+### nearest
+
+[Nearest neighbour interpolation][3]. Suitable for image enlargement only.
+
+### bilinear
+
+[Bilinear interpolation][4]. Faster than bicubic but with less smooth results.
+
+### bicubic
+
+[Bicubic interpolation][5] (the default).
+
+### locallyBoundedBicubic
+
+[LBB interpolation][6]. Prevents some "[acutance][7]" but typically reduces performance by a factor of 2.
+
+### nohalo
+
+[Nohalo interpolation][8]. Prevents acutance but typically reduces performance by a factor of 3.
+
+### vertexSplitQuadraticBasisSpline
+
+[VSQBS interpolation][9]. Prevents "staircasing" when enlarging.
+
 ## versions
 
 An Object containing the version numbers of libvips and its dependencies.
@@ -31,10 +61,10 @@ useful for determining how much working memory is required for a particular task
 
 ### Parameters
 
--   `options` **([Object][1] \| [boolean][2])** Object with the following attributes, or boolean where true uses default cache settings and false removes all caching (optional, default `true`)
-    -   `options.memory` **[number][3]** is the maximum memory in MB to use for this cache (optional, default `50`)
-    -   `options.files` **[number][3]** is the maximum number of files to hold open (optional, default `20`)
-    -   `options.items` **[number][3]** is the maximum number of operations to cache (optional, default `100`)
+-   `options` **([Object][1] \| [boolean][10])** Object with the following attributes, or boolean where true uses default cache settings and false removes all caching (optional, default `true`)
+    -   `options.memory` **[number][11]** is the maximum memory in MB to use for this cache (optional, default `50`)
+    -   `options.files` **[number][11]** is the maximum number of files to hold open (optional, default `20`)
+    -   `options.items` **[number][11]** is the maximum number of operations to cache (optional, default `100`)
 
 ### Examples
 
@@ -64,7 +94,7 @@ This method always returns the current concurrency.
 
 ### Parameters
 
--   `concurrency` **[number][3]?** 
+-   `concurrency` **[number][11]?** 
 
 ### Examples
 
@@ -74,7 +104,7 @@ sharp.concurrency(2); // 2
 sharp.concurrency(0); // 4
 ```
 
-Returns **[number][3]** concurrency
+Returns **[number][11]** concurrency
 
 ## queue
 
@@ -116,7 +146,7 @@ by taking advantage of the SIMD vector unit of the CPU, e.g. Intel SSE and ARM N
 
 ### Parameters
 
--   `simd` **[boolean][2]**  (optional, default `true`)
+-   `simd` **[boolean][10]**  (optional, default `true`)
 
 ### Examples
 
@@ -130,10 +160,26 @@ const simd = sharp.simd(false);
 // prevent libvips from using liborc at runtime
 ```
 
-Returns **[boolean][2]** 
+Returns **[boolean][10]** 
 
 [1]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
 
-[2]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
+[2]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
 
-[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number
+[3]: http://en.wikipedia.org/wiki/Nearest-neighbor_interpolation
+
+[4]: http://en.wikipedia.org/wiki/Bilinear_interpolation
+
+[5]: http://en.wikipedia.org/wiki/Bicubic_interpolation
+
+[6]: https://github.com/jcupitt/libvips/blob/master/libvips/resample/lbb.cpp#L100
+
+[7]: http://en.wikipedia.org/wiki/Acutance
+
+[8]: http://eprints.soton.ac.uk/268086/
+
+[9]: https://github.com/jcupitt/libvips/blob/master/libvips/resample/vsqbs.cpp#L48
+
+[10]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
+
+[11]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number

lib/constructor.js

@@ -155,6 +155,13 @@ const Sharp = function (input, options) {
     extendRight: 0,
     extendBackground: [0, 0, 0, 255],
     withoutEnlargement: false,
+    affineMatrix: [],
+    affineBackground: [0, 0, 0, 255],
+    affineIdx: 0,
+    affineIdy: 0,
+    affineOdx: 0,
+    affineOdy: 0,
+    affineInterpolator: this.constructor.interpolators.bilinear,
     kernel: 'lanczos3',
     fastShrinkOnLoad: true,
     // operations

lib/operation.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const { flatten: flattenArray } = require('array-flatten');
 const color = require('color');
 const is = require('./is');
 
@@ -82,6 +83,103 @@ function flop (flop) {
   return this;
 }
 
+/**
+ * Perform an affine transform on an image. This operation will always occur after resizing, extraction and rotation, if any.
+ *
+ * You must provide an array of length 4 or a 2x2 affine transformation matrix.
+ * By default, new pixels are filled with a black background. You can provide a background color with the `background` option.
+ * A particular interpolator may also be specified. Set the `interpolator` option to an attribute of the `sharp.interpolator` Object e.g. `sharp.interpolator.nohalo`.
+ *
+ * In the case of a 2x2 matrix, the transform is:
+ * - X = `matrix[0, 0]` \* (x + `idx`) + `matrix[0, 1]` \* (y + `idy`) + `odx`
+ * - Y = `matrix[1, 0]` \* (x + `idx`) + `matrix[1, 1]` \* (y + `idy`) + `ody`
+ *
+ * where:
+ * - x and y are the coordinates in input image.
+ * - X and Y are the coordinates in output image.
+ * - (0,0) is the upper left corner.
+ *
+ * @since 0.27.0
+ *
+ * @example
+ * const pipeline = sharp()
+ *   .affine([[1, 0.3], [0.1, 0.7]], {
+ *      background: 'white',
+ *      interpolate: sharp.interpolators.nohalo
+ *   })
+ *   .toBuffer((err, outputBuffer, info) => {
+ *      // outputBuffer contains the transformed image
+ *      // info.width and info.height contain the new dimensions
+ *   });
+ *
+ * inputStream
+ *   .pipe(pipeline);
+ *
+ * @param {Array<Array<number>>|Array<number>} matrix - affine transformation matrix
+ * @param {Object} [options] - if present, is an Object with optional attributes.
+ * @param {String|Object} [options.background="#000000"] - parsed by the [color](https://www.npmjs.org/package/color) module to extract values for red, green, blue and alpha.
+ * @param {Number} [options.idx=0] - input horizontal offset
+ * @param {Number} [options.idy=0] - input vertical offset
+ * @param {Number} [options.odx=0] - output horizontal offset
+ * @param {Number} [options.ody=0] - output vertical offset
+ * @param {String} [options.interpolator=sharp.interpolators.bicubic] - interpolator
+ * @returns {Sharp}
+ * @throws {Error} Invalid parameters
+ */
+function affine (matrix, options) {
+  const flatMatrix = flattenArray(matrix);
+  if (flatMatrix.length === 4 && flatMatrix.every(is.number)) {
+    this.options.affineMatrix = flatMatrix;
+  } else {
+    throw is.invalidParameterError('matrix', '1x4 or 2x2 array', matrix);
+  }
+
+  if (is.defined(options)) {
+    if (is.object(options)) {
+      this._setBackgroundColourOption('affineBackground', options.background);
+      if (is.defined(options.idx)) {
+        if (is.number(options.idx)) {
+          this.options.affineIdx = options.idx;
+        } else {
+          throw is.invalidParameterError('options.idx', 'number', options.idx);
+        }
+      }
+      if (is.defined(options.idy)) {
+        if (is.number(options.idy)) {
+          this.options.affineIdy = options.idy;
+        } else {
+          throw is.invalidParameterError('options.idy', 'number', options.idy);
+        }
+      }
+      if (is.defined(options.odx)) {
+        if (is.number(options.odx)) {
+          this.options.affineOdx = options.odx;
+        } else {
+          throw is.invalidParameterError('options.odx', 'number', options.odx);
+        }
+      }
+      if (is.defined(options.ody)) {
+        if (is.number(options.ody)) {
+          this.options.affineOdy = options.ody;
+        } else {
+          throw is.invalidParameterError('options.ody', 'number', options.ody);
+        }
+      }
+      if (is.defined(options.interpolator)) {
+        if (is.inArray(options.interpolator, Object.values(this.constructor.interpolators))) {
+          this.options.affineInterpolator = options.interpolator;
+        } else {
+          throw is.invalidParameterError('options.interpolator', 'valid interpolator name', options.interpolator);
+        }
+      }
+    } else {
+      throw is.invalidParameterError('options', 'object', options);
+    }
+  }
+
+  return this;
+}
+
 /**
  * Sharpen the image.
  * When used without parameters, performs a fast, mild sharpen of the output image.
@@ -482,6 +580,7 @@ module.exports = function (Sharp) {
     rotate,
     flip,
     flop,
+    affine,
     sharpen,
     median,
     blur,

lib/utility.js

@@ -13,6 +13,26 @@ const sharp = require('../build/Release/sharp.node');
  */
 const format = sharp.format();
 
+/**
+ * An Object containing the available interpolators and their proper values
+ * @readonly
+ * @enum {string}
+ */
+const interpolators = {
+  /** [Nearest neighbour interpolation](http://en.wikipedia.org/wiki/Nearest-neighbor_interpolation). Suitable for image enlargement only. */
+  nearest: 'nearest',
+  /** [Bilinear interpolation](http://en.wikipedia.org/wiki/Bilinear_interpolation). Faster than bicubic but with less smooth results. */
+  bilinear: 'bilinear',
+  /** [Bicubic interpolation](http://en.wikipedia.org/wiki/Bicubic_interpolation) (the default). */
+  bicubic: 'bicubic',
+  /** [LBB interpolation](https://github.com/jcupitt/libvips/blob/master/libvips/resample/lbb.cpp#L100). Prevents some "[acutance](http://en.wikipedia.org/wiki/Acutance)" but typically reduces performance by a factor of 2. */
+  locallyBoundedBicubic: 'lbb',
+  /** [Nohalo interpolation](http://eprints.soton.ac.uk/268086/). Prevents acutance but typically reduces performance by a factor of 3. */
+  nohalo: 'nohalo',
+  /** [VSQBS interpolation](https://github.com/jcupitt/libvips/blob/master/libvips/resample/vsqbs.cpp#L48). Prevents "staircasing" when enlarging. */
+  vertexSplitQuadraticBasisSpline: 'vsqbs'
+};
+
 /**
  * An Object containing the version numbers of libvips and its dependencies.
  * @member
@@ -146,6 +166,7 @@ module.exports = function (Sharp) {
     Sharp[f.name] = f;
   });
   Sharp.format = format;
+  Sharp.interpolators = interpolators;
   Sharp.versions = versions;
   Sharp.queue = queue;
 };

package.json

@@ -69,7 +69,8 @@
     "Edward Silverton <e.silverton@gmail.com>",
     "Roman Malieiev <aromaleev@gmail.com>",
     "Tomas Szabo <tomas.szabo@deftomat.com>",
-    "Robert O'Rourke <robert@o-rourke.org>"
+    "Robert O'Rourke <robert@o-rourke.org>",
+    "Guillermo Alfonso Varela Chouciño <guillevch@gmail.com>"
   ],
   "scripts": {
     "install": "(node install/libvips && node install/dll-copy && prebuild-install) || (node-gyp rebuild && node install/dll-copy)",
@@ -112,6 +113,7 @@
     "vips"
   ],
   "dependencies": {
+    "array-flatten": "^3.0.0",
     "color": "^3.1.2",
     "detect-libc": "^1.0.3",
     "node-addon-api": "^3.0.2",

src/common.cc

@@ -54,13 +54,13 @@ namespace sharp {
   bool AttrAsBool(Napi::Object obj, std::string attr) {
     return obj.Get(attr).As<Napi::Boolean>().Value();
   }
-  std::vector<double> AttrAsRgba(Napi::Object obj, std::string attr) {
-    Napi::Array background = obj.Get(attr).As<Napi::Array>();
-    std::vector<double> rgba(background.Length());
-    for (unsigned int i = 0; i < background.Length(); i++) {
-      rgba[i] = AttrAsDouble(background, i);
+  std::vector<double> AttrAsVectorOfDouble(Napi::Object obj, std::string attr) {
+    Napi::Array napiArray = obj.Get(attr).As<Napi::Array>();
+    std::vector<double> vectorOfDouble(napiArray.Length());
+    for (unsigned int i = 0; i < napiArray.Length(); i++) {
+      vectorOfDouble[i] = AttrAsDouble(napiArray, i);
     }
-    return rgba;
+    return vectorOfDouble;
   }
   std::vector<int32_t> AttrAsInt32Vector(Napi::Object obj, std::string attr) {
     Napi::Array array = obj.Get(attr).As<Napi::Array>();
@@ -109,7 +109,7 @@ namespace sharp {
       descriptor->createChannels = AttrAsUint32(input, "createChannels");
       descriptor->createWidth = AttrAsUint32(input, "createWidth");
       descriptor->createHeight = AttrAsUint32(input, "createHeight");
-      descriptor->createBackground = AttrAsRgba(input, "createBackground");
+      descriptor->createBackground = AttrAsVectorOfDouble(input, "createBackground");
     }
     // Limit input images to a given number of pixels, where pixels = width * height
     descriptor->limitInputPixels = AttrAsUint32(input, "limitInputPixels");

src/common.h

@@ -92,7 +92,7 @@ namespace sharp {
   double AttrAsDouble(Napi::Object obj, std::string attr);
   double AttrAsDouble(Napi::Object obj, unsigned int const attr);
   bool AttrAsBool(Napi::Object obj, std::string attr);
-  std::vector<double> AttrAsRgba(Napi::Object obj, std::string attr);
+  std::vector<double> AttrAsVectorOfDouble(Napi::Object obj, std::string attr);
   std::vector<int32_t> AttrAsInt32Vector(Napi::Object obj, std::string attr);
 
   // Create an InputDescriptor instance from a Napi::Object describing an input image

src/pipeline.cc

@@ -485,6 +485,18 @@ class PipelineWorker : public Napi::AsyncWorker {
           baton->leftOffsetPost, baton->topOffsetPost, baton->widthPost, baton->heightPost);
       }
 
+      // Affine transform
+      if (baton->affineMatrix.size() > 0) {
+        std::vector<double> background;
+        std::tie(image, background) = sharp::ApplyAlpha(image, baton->affineBackground);
+        image = image.affine(baton->affineMatrix, VImage::option()->set("background", background)
+          ->set("idx", baton->affineIdx)
+          ->set("idy", baton->affineIdy)
+          ->set("odx", baton->affineOdx)
+          ->set("ody", baton->affineOdy)
+          ->set("interpolate", baton->affineInterpolator));
+      }
+
       // Extend edges
       if (baton->extendTop > 0 || baton->extendBottom > 0 || baton->extendLeft > 0 || baton->extendRight > 0) {
         std::vector<double> background;
@@ -1249,7 +1261,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   // Resize options
   baton->withoutEnlargement = sharp::AttrAsBool(options, "withoutEnlargement");
   baton->position = sharp::AttrAsInt32(options, "position");
-  baton->resizeBackground = sharp::AttrAsRgba(options, "resizeBackground");
+  baton->resizeBackground = sharp::AttrAsVectorOfDouble(options, "resizeBackground");
   baton->kernel = sharp::AttrAsStr(options, "kernel");
   baton->fastShrinkOnLoad = sharp::AttrAsBool(options, "fastShrinkOnLoad");
   // Join Channel Options
@@ -1262,7 +1274,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   }
   // Operators
   baton->flatten = sharp::AttrAsBool(options, "flatten");
-  baton->flattenBackground = sharp::AttrAsRgba(options, "flattenBackground");
+  baton->flattenBackground = sharp::AttrAsVectorOfDouble(options, "flattenBackground");
   baton->negate = sharp::AttrAsBool(options, "negate");
   baton->blurSigma = sharp::AttrAsDouble(options, "blurSigma");
   baton->brightness = sharp::AttrAsDouble(options, "brightness");
@@ -1284,7 +1296,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->useExifOrientation = sharp::AttrAsBool(options, "useExifOrientation");
   baton->angle = sharp::AttrAsInt32(options, "angle");
   baton->rotationAngle = sharp::AttrAsDouble(options, "rotationAngle");
-  baton->rotationBackground = sharp::AttrAsRgba(options, "rotationBackground");
+  baton->rotationBackground = sharp::AttrAsVectorOfDouble(options, "rotationBackground");
   baton->rotateBeforePreExtract = sharp::AttrAsBool(options, "rotateBeforePreExtract");
   baton->flip = sharp::AttrAsBool(options, "flip");
   baton->flop = sharp::AttrAsBool(options, "flop");
@@ -1292,8 +1304,15 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->extendBottom = sharp::AttrAsInt32(options, "extendBottom");
   baton->extendLeft = sharp::AttrAsInt32(options, "extendLeft");
   baton->extendRight = sharp::AttrAsInt32(options, "extendRight");
-  baton->extendBackground = sharp::AttrAsRgba(options, "extendBackground");
+  baton->extendBackground = sharp::AttrAsVectorOfDouble(options, "extendBackground");
   baton->extractChannel = sharp::AttrAsInt32(options, "extractChannel");
+  baton->affineMatrix = sharp::AttrAsVectorOfDouble(options, "affineMatrix");
+  baton->affineBackground = sharp::AttrAsVectorOfDouble(options, "affineBackground");
+  baton->affineIdx = sharp::AttrAsDouble(options, "affineIdx");
+  baton->affineIdy = sharp::AttrAsDouble(options, "affineIdy");
+  baton->affineOdx = sharp::AttrAsDouble(options, "affineOdx");
+  baton->affineOdy = sharp::AttrAsDouble(options, "affineOdy");
+  baton->affineInterpolator = vips::VInterpolate::new_from_name(sharp::AttrAsStr(options, "affineInterpolator").data());
 
   baton->removeAlpha = sharp::AttrAsBool(options, "removeAlpha");
   baton->ensureAlpha = sharp::AttrAsBool(options, "ensureAlpha");
@@ -1392,7 +1411,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->tileSize = sharp::AttrAsUint32(options, "tileSize");
   baton->tileOverlap = sharp::AttrAsUint32(options, "tileOverlap");
   baton->tileAngle = sharp::AttrAsInt32(options, "tileAngle");
-  baton->tileBackground = sharp::AttrAsRgba(options, "tileBackground");
+  baton->tileBackground = sharp::AttrAsVectorOfDouble(options, "tileBackground");
   baton->tileSkipBlanks = sharp::AttrAsInt32(options, "tileSkipBlanks");
   baton->tileContainer = static_cast<VipsForeignDzContainer>(
     vips_enum_from_nick(nullptr, VIPS_TYPE_FOREIGN_DZ_CONTAINER,

src/pipeline.h

@@ -119,6 +119,13 @@ struct PipelineBaton {
   int extendRight;
   std::vector<double> extendBackground;
   bool withoutEnlargement;
+  std::vector<double> affineMatrix;
+  std::vector<double> affineBackground;
+  double affineIdx;
+  double affineIdy;
+  double affineOdx;
+  double affineOdy;
+  vips::VInterpolate affineInterpolator;
   int jpegQuality;
   bool jpegProgressive;
   std::string jpegChromaSubsampling;
@@ -231,6 +238,13 @@ struct PipelineBaton {
     extendRight(0),
     extendBackground{ 0.0, 0.0, 0.0, 255.0 },
     withoutEnlargement(false),
+    affineMatrix{ 1.0, 0.0, 0.0, 1.0 },
+    affineBackground{ 0.0, 0.0, 0.0, 255.0 },
+    affineIdx(0),
+    affineIdy(0),
+    affineOdx(0),
+    affineOdy(0),
+    affineInterpolator(vips::VInterpolate::new_from_name("bicubic")),
     jpegQuality(80),
     jpegProgressive(false),
     jpegChromaSubsampling("4:2:0"),

test/unit/affine.js

@@ -0,0 +1,175 @@
+'use strict';
+
+const assert = require('assert');
+
+const sharp = require('../../');
+const fixtures = require('../fixtures');
+
+describe('Affine transform', () => {
+  describe('Invalid input', () => {
+    it('Missing matrix', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine();
+      });
+    });
+    it('Invalid 1d matrix', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine(['123', 123, 123, 123]);
+      });
+    });
+    it('Invalid 2d matrix', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([[123, 123], [null, 123]]);
+      });
+    });
+    it('Invalid options parameter type', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([[1, 0], [0, 1]], 'invalid options type');
+      });
+    });
+    it('Invalid background color', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([4, 4, 4, 4], { background: 'not a color' });
+      });
+    });
+    it('Invalid idx offset type', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([[4, 4], [4, 4]], { idx: 'invalid idx type' });
+      });
+    });
+    it('Invalid idy offset type', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([4, 4, 4, 4], { idy: 'invalid idy type' });
+      });
+    });
+    it('Invalid odx offset type', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([[4, 4], [4, 4]], { odx: 'invalid odx type' });
+      });
+    });
+    it('Invalid ody offset type', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([[4, 4], [4, 4]], { ody: 'invalid ody type' });
+      });
+    });
+    it('Invalid interpolator', () => {
+      assert.throws(() => {
+        sharp(fixtures.inputJpg)
+          .affine([[4, 4], [4, 4]], { interpolator: 'cubic' });
+      });
+    });
+  });
+  it('Applies identity matrix', done => {
+    const input = fixtures.inputJpg;
+    sharp(input)
+      .affine([[1, 0], [0, 1]])
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(input, data, done);
+      });
+  });
+  it('Applies resize affine matrix', done => {
+    const input = fixtures.inputJpg;
+    const inputWidth = 2725;
+    const inputHeight = 2225;
+    sharp(input)
+      .affine([[0.2, 0], [0, 1.5]])
+      .toBuffer((err, data, info) => {
+        if (err) throw err;
+        fixtures.assertSimilar(input, data, done);
+        assert.strictEqual(info.width, Math.ceil(inputWidth * 0.2));
+        assert.strictEqual(info.height, Math.ceil(inputHeight * 1.5));
+      });
+  });
+  it('Resizes and applies affine transform', done => {
+    const input = fixtures.inputJpg;
+    sharp(input)
+      .resize(500, 500)
+      .affine([[0.5, 1], [1, 0.5]])
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(data, fixtures.expected('affine-resize-expected.jpg'), done);
+      });
+  });
+  it('Extracts and applies affine transform', done => {
+    sharp(fixtures.inputJpg)
+      .extract({ left: 300, top: 300, width: 600, height: 600 })
+      .affine([0.3, 0, -0.5, 0.3])
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(data, fixtures.expected('affine-extract-expected.jpg'), done);
+      });
+  });
+  it('Rotates and applies affine transform', done => {
+    sharp(fixtures.inputJpg320x240)
+      .rotate(90)
+      .affine([[-1.2, 0], [0, -1.2]])
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(data, fixtures.expected('affine-rotate-expected.jpg'), done);
+      });
+  });
+  it('Extracts, rotates and applies affine transform', done => {
+    sharp(fixtures.inputJpg)
+      .extract({ left: 1000, top: 1000, width: 200, height: 200 })
+      .rotate(45, { background: 'blue' })
+      .affine([[2, 1], [2, -0.5]], { background: 'red' })
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(fixtures.expected('affine-extract-rotate-expected.jpg'), data, done);
+      });
+  });
+  it('Applies affine transform with background color', done => {
+    sharp(fixtures.inputJpg320x240)
+      .rotate(180)
+      .affine([[-1.5, 1.2], [-1, 1]], { background: 'red' })
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(fixtures.expected('affine-background-expected.jpg'), data, done);
+      });
+  });
+  it('Applies affine transform with background color and output offsets', done => {
+    sharp(fixtures.inputJpg320x240)
+      .rotate(180)
+      .affine([[-2, 1.5], [-1, 2]], { background: 'blue', odx: 40, ody: -100 })
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(fixtures.expected('affine-background-output-offsets-expected.jpg'), data, done);
+      });
+  });
+  it('Applies affine transform with background color and all offsets', done => {
+    sharp(fixtures.inputJpg320x240)
+      .rotate(180)
+      .affine([[-1.2, 1.8], [-1, 2]], { background: 'yellow', idx: 10, idy: -40, odx: 10, ody: -50 })
+      .toBuffer((err, data) => {
+        if (err) throw err;
+        fixtures.assertSimilar(fixtures.expected('affine-background-all-offsets-expected.jpg'), data, done);
+      });
+  });
+  describe('Interpolations', () => {
+    const input = fixtures.inputJpg320x240;
+    const inputWidth = 320;
+    const inputHeight = 240;
+    for (const interp in sharp.interpolators) {
+      it(`Performs 2x upscale with ${interp} interpolation`, done => {
+        sharp(input)
+          .affine([[2, 0], [0, 2]], { interpolator: sharp.interpolators[interp] })
+          .toBuffer((err, data, info) => {
+            if (err) throw err;
+            assert.strictEqual(info.width, Math.ceil(inputWidth * 2));
+            assert.strictEqual(info.height, Math.ceil(inputHeight * 2));
+            fixtures.assertSimilar(fixtures.expected(`affine-${sharp.interpolators[interp]}-2x-upscale-expected.jpg`), data, done);
+          });
+      });
+    }
+  });
+});