Add premultiplied boolean flag for raw pixel data input (#2685)

docs/api-constructor.md

@@ -37,6 +37,8 @@ Implements the [stream.Duplex][1] class.
         *   `options.raw.width` **[number][8]?** integral number of pixels wide.
         *   `options.raw.height` **[number][8]?** integral number of pixels high.
         *   `options.raw.channels` **[number][8]?** integral number of channels, between 1 and 4.
+        *   `options.raw.premultiplied` **[boolean][7]?** specifies that the raw input has already been premultiplied, set to `true`
+            to avoid sharp premultiplying the image. (optional, default `false`)
     *   `options.create` **[Object][6]?** describes a new image to be created.
 
         *   `options.create.width` **[number][8]?** integral number of pixels wide.

lib/constructor.js

@@ -139,6 +139,8 @@ const debuglog = util.debuglog('sharp');
  * @param {number} [options.raw.width] - integral number of pixels wide.
  * @param {number} [options.raw.height] - integral number of pixels high.
  * @param {number} [options.raw.channels] - integral number of channels, between 1 and 4.
+ * @param {boolean} [options.raw.premultiplied] - specifies that the raw input has already been premultiplied, set to `true`
+ *  to avoid sharp premultiplying the image. (optional, default `false`)
  * @param {Object} [options.create] - describes a new image to be created.
  * @param {number} [options.create.width] - integral number of pixels wide.
  * @param {number} [options.create.height] - integral number of pixels high.

lib/input.js

@@ -103,6 +103,7 @@ function _createInputDescriptor (input, inputOptions, containerOptions) {
         inputDescriptor.rawWidth = inputOptions.raw.width;
         inputDescriptor.rawHeight = inputOptions.raw.height;
         inputDescriptor.rawChannels = inputOptions.raw.channels;
+        inputDescriptor.rawPremultiplied = !!inputOptions.raw.premultiplied;
       } else {
         throw new Error('Expected width, height and channels for raw pixel input');
       }

package.json

@@ -75,7 +75,8 @@
     "Manan Jadhav <manan@motionden.com>",
     "Leon Radley <leon@radley.se>",
     "alza54 <alza54@thiocod.in>",
-    "Jacob Smith <jacob@frende.me>"
+    "Jacob Smith <jacob@frende.me>",
+    "Michael Nutt <michael@nutt.im>"
   ],
   "scripts": {
     "install": "(node install/libvips && node install/dll-copy && prebuild-install) || (node-gyp rebuild && node install/dll-copy)",

src/common.cc

@@ -95,6 +95,7 @@ namespace sharp {
       descriptor->rawChannels = AttrAsUint32(input, "rawChannels");
       descriptor->rawWidth = AttrAsUint32(input, "rawWidth");
       descriptor->rawHeight = AttrAsUint32(input, "rawHeight");
+      descriptor->rawPremultiplied = AttrAsBool(input, "rawPremultiplied");
     }
     // Multi-page input (GIF, TIFF, PDF)
     if (HasAttr(input, "pages")) {
@@ -302,6 +303,9 @@ namespace sharp {
         } else {
           image.get_image()->Type = VIPS_INTERPRETATION_sRGB;
         }
+        if (descriptor->rawPremultiplied) {
+          image = image.unpremultiply();
+        }
         imageType = ImageType::RAW;
       } else {
         // Compressed data

src/common.h

@@ -57,6 +57,7 @@ namespace sharp {
     int rawChannels;
     int rawWidth;
     int rawHeight;
+    bool rawPremultiplied;
     int pages;
     int page;
     int level;
@@ -80,6 +81,7 @@ namespace sharp {
       rawChannels(0),
       rawWidth(0),
       rawHeight(0),
+      rawPremultiplied(false),
       pages(1),
       page(0),
       level(0),

test/fixtures/index.js

@@ -90,6 +90,7 @@ module.exports = {
   inputPngEmbed: getPath('embedgravitybird.png'), // Released to sharp under a CC BY 4.0
   inputPngRGBWithAlpha: getPath('2569067123_aca715a2ee_o.png'), // http://www.flickr.com/photos/grizdave/2569067123/ (same as inputJpg)
   inputPngImageInAlpha: getPath('image-in-alpha.png'), // https://github.com/lovell/sharp/issues/1597
+  inputPngSolidAlpha: getPath('with-alpha.png'), // https://github.com/lovell/sharp/issues/1599
 
   inputWebP: getPath('4.webp'), // http://www.gstatic.com/webp/gallery/4.webp
   inputWebPWithTransparency: getPath('5_webp_a.webp'), // http://www.gstatic.com/webp/gallery3/5_webp_a.webp

test/unit/raw.js

@@ -107,6 +107,52 @@ describe('Raw pixel data', function () {
         });
     });
 
+    it('RGBA premultiplied', function (done) {
+      // Convert to raw pixel data
+      sharp(fixtures.inputPngSolidAlpha)
+        .resize(256)
+        .raw()
+        .toBuffer(function (err, data, info) {
+          if (err) throw err;
+          assert.strictEqual(256, info.width);
+          assert.strictEqual(192, info.height);
+          assert.strictEqual(4, info.channels);
+
+          const originalData = Buffer.from(data);
+
+          // Premultiply image data
+          for (let i = 0; i < data.length; i += 4) {
+            const alpha = data[i + 3];
+            const norm = alpha / 255;
+
+            if (alpha < 255) {
+              data[i] = Math.round(data[i] * norm);
+              data[i + 1] = Math.round(data[i + 1] * norm);
+              data[i + 2] = Math.round(data[i + 2] * norm);
+            }
+          }
+
+          // Convert back to PNG
+          sharp(data, {
+            raw: {
+              width: info.width,
+              height: info.height,
+              channels: info.channels,
+              premultiplied: true
+            }
+          })
+            .raw()
+            .toBuffer(function (err, data, info) {
+              if (err) throw err;
+              assert.strictEqual(256, info.width);
+              assert.strictEqual(192, info.height);
+              assert.strictEqual(4, info.channels);
+              assert.equal(data.compare(originalData), 0, 'output buffer matches unpremultiplied input buffer');
+              done();
+            });
+        });
+    });
+
     it('JPEG to raw Stream and back again', function (done) {
       const width = 32;
       const height = 24;