Expose libvips centre option, mimics *magick +0.5px convention

lovell · Nov 4, 2016 · 2c7a846 · 2c7a846
1 parent deb978b
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Showing 9 changed files with 202 additions and 164 deletions.
diff --git a/docs/api-output.md b/docs/api-output.md
@@ -68,6 +68,7 @@ Use these JPEG options for output image.
 -   `trellisQuantisation` **\[[Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)]** apply trellis quantisation, requires mozjpeg (optional, default `false`)
 -   `overshootDeringing` **\[[Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)]** apply overshoot deringing, requires mozjpeg (optional, default `false`)
 -   `optimiseScans` **\[[Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)]** optimise progressive scans, forces progressive, requires mozjpeg (optional, default `false`)
+-   `optimizeScans` **\[[Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)]** alternative spelling of optimiseScans (optional, default `false`)
 
 
 -   Throws **[Error](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)** Invalid options

diff --git a/docs/api-resize.md b/docs/api-resize.md
@@ -27,6 +27,8 @@ Possible enlargement interpolators are:
 -   `options` **\[[Object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)]** 
     -   `options.kernel` **\[[String](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)]** the kernel to use for image reduction. (optional, default `'lanczos3'`)
     -   `options.interpolator` **\[[String](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)]** the interpolator to use for image enlargement. (optional, default `'bicubic'`)
+    -   `options.centreSampling` **\[[Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)]** use \*magick centre sampling convention instead of corner sampling. (optional, default `false`)
+    -   `options.centerSampling` **\[[Boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)]** alternative spelling of centreSampling. (optional, default `false`)
 
 **Examples**
 

diff --git a/docs/changelog.md b/docs/changelog.md
@@ -15,6 +15,9 @@ Requires libvips v8.4.2.
   Access to these is now via output format functions, for example `quality(n)`
     is now `jpeg({quality: n})` and/or `webp({quality: n})`.
 
+* Expose libvips' "centre" resize option to mimic *magick's +0.5px convention.
+  [#568](https://github.com/lovell/sharp/issues/568)
+
 * Ensure support for embedded base64 PNG and JPEG images within an SVG.
   [#601](https://github.com/lovell/sharp/issues/601)
   [@dynamite-ready](https://github.com/dynamite-ready)

diff --git a/lib/constructor.js b/lib/constructor.js
@@ -102,6 +102,7 @@ const Sharp = function (input, options) {
     withoutEnlargement: false,
     kernel: 'lanczos3',
     interpolator: 'bicubic',
+    centreSampling: false,
     // operations
     background: [0, 0, 0, 255],
     flatten: false,

diff --git a/lib/output.js b/lib/output.js
@@ -115,14 +115,14 @@ const jpeg = function jpeg (options) {
         throw new Error('Invalid chromaSubsampling (4:2:0, 4:4:4) ' + options.chromaSubsampling);
       }
     }
-    options.trellisQuantisation = options.trellisQuantisation || options.trellisQuantization;
+    options.trellisQuantisation = is.bool(options.trellisQuantization) ? options.trellisQuantization : options.trellisQuantisation;
     if (is.defined(options.trellisQuantisation)) {
       this._setBooleanOption('jpegTrellisQuantisation', options.trellisQuantisation);
     }
     if (is.defined(options.overshootDeringing)) {
       this._setBooleanOption('jpegOvershootDeringing', options.overshootDeringing);
     }
-    options.optimiseScans = is.bool(options.optimiseScans) ? options.optimiseScans : options.optimizeScans;
+    options.optimiseScans = is.bool(options.optimizeScans) ? options.optimizeScans : options.optimiseScans;
     if (is.defined(options.optimiseScans)) {
       this._setBooleanOption('jpegOptimiseScans', options.optimiseScans);
       if (options.optimiseScans) {

diff --git a/lib/resize.js b/lib/resize.js
@@ -94,6 +94,8 @@ const interpolator = {
  * @param {Object} [options]
  * @param {String} [options.kernel='lanczos3'] - the kernel to use for image reduction.
  * @param {String} [options.interpolator='bicubic'] - the interpolator to use for image enlargement.
+ * @param {Boolean} [options.centreSampling=false] - use *magick centre sampling convention instead of corner sampling.
+ * @param {Boolean} [options.centerSampling=false] - alternative spelling of centreSampling.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
  */
@@ -133,6 +135,11 @@ const resize = function resize (width, height, options) {
         throw new Error('Invalid interpolator ' + options.interpolator);
       }
     }
+    // Centre sampling
+    options.centreSampling = is.bool(options.centerSampling) ? options.centerSampling : options.centreSampling;
+    if (is.defined(options.centreSampling)) {
+      this._setBooleanOption('centreSampling', options.centreSampling);
+    }
   }
   return this;
 };

diff --git a/src/pipeline.cc b/src/pipeline.cc
@@ -388,10 +388,16 @@ class PipelineWorker : public Nan::AsyncWorker {
             throw vips::VError("Unknown kernel");
           }
           if (yresidual < 1.0) {
-            image = image.reducev(1.0 / yresidual, VImage::option()->set("kernel", kernel));
+            image = image.reducev(1.0 / yresidual, VImage::option()
+              ->set("kernel", kernel)
+              ->set("centre", baton->centreSampling)
+            );
           }
           if (xresidual < 1.0) {
-            image = image.reduceh(1.0 / xresidual, VImage::option()->set("kernel", kernel));
+            image = image.reduceh(1.0 / xresidual, VImage::option()
+              ->set("kernel", kernel)
+              ->set("centre", baton->centreSampling)
+            );
           }
         }
         // Perform affine enlargement
@@ -1063,6 +1069,7 @@ NAN_METHOD(pipeline) {
   baton->crop = AttrTo<int32_t>(options, "crop");
   baton->kernel = AttrAsStr(options, "kernel");
   baton->interpolator = AttrAsStr(options, "interpolator");
+  baton->centreSampling = AttrTo<bool>(options, "centreSampling");
   // Join Channel Options
   if(HasAttr(options, "joinChannelIn")) {
     v8::Local<v8::Object> joinChannelObject = Nan::Get(options, Nan::New("joinChannelIn").ToLocalChecked())

diff --git a/src/pipeline.h b/src/pipeline.h
@@ -50,6 +50,7 @@ struct PipelineBaton {
   int cropCalcTop;
   std::string kernel;
   std::string interpolator;
+  bool centreSampling;
   double background[4];
   bool flatten;
   bool negate;
@@ -119,6 +120,7 @@ struct PipelineBaton {
     crop(0),
     cropCalcLeft(-1),
     cropCalcTop(-1),
+    centreSampling(false),
     flatten(false),
     negate(false),
     blurSigma(0.0),