Expose reoptimise palette option for GIF output

docs/api-output.md

@@ -321,10 +321,14 @@ Use these GIF options for the output image.
 
 The first entry in the palette is reserved for transparency.
 
+The palette of the input image will be re-used if possible.
+
 ### Parameters
 
 *   `options` **[Object][6]?** output options
 
+    *   `options.reoptimise` **[boolean][10]** always generate new palettes (slow), re-use existing by default (optional, default `false`)
+    *   `options.reoptimize` **[boolean][10]** alternative spelling of `options.reoptimise` (optional, default `false`)
     *   `options.colours` **[number][12]** maximum number of palette entries, including transparency, between 2 and 256 (optional, default `256`)
     *   `options.colors` **[number][12]** alternative spelling of `options.colours` (optional, default `256`)
     *   `options.effort` **[number][12]** CPU effort, between 1 (fastest) and 10 (slowest) (optional, default `7`)

docs/changelog.md

@@ -8,6 +8,8 @@ Requires libvips v8.13.0
 
 * Drop support for Node.js 12, now requires Node.js >= 14.15.0.
 
+* GIF output now re-uses input palette if possible. Use `reoptimise` option to generate a new palette.
+
 * Add WebP `minSize` and `mixed` options for greater control over animation frames.
 
 * Use combined bounding box of alpha and non-alpha channels for `trim` operation.

lib/constructor.js

@@ -256,6 +256,7 @@ const Sharp = function (input, options) {
     gifBitdepth: 8,
     gifEffort: 7,
     gifDither: 1,
+    gifReoptimise: false,
     tiffQuality: 80,
     tiffCompression: 'jpeg',
     tiffPredictor: 'horizontal',

lib/output.js

@@ -524,6 +524,8 @@ function webp (options) {
  *
  * The first entry in the palette is reserved for transparency.
  *
+ * The palette of the input image will be re-used if possible.
+ *
  * @since 0.30.0
  *
  * @example
@@ -545,6 +547,8 @@ function webp (options) {
  *   .toBuffer();
  *
  * @param {Object} [options] - output options
+ * @param {boolean} [options.reoptimise=false] - always generate new palettes (slow), re-use existing by default
+ * @param {boolean} [options.reoptimize=false] - alternative spelling of `options.reoptimise`
  * @param {number} [options.colours=256] - maximum number of palette entries, including transparency, between 2 and 256
  * @param {number} [options.colors=256] - alternative spelling of `options.colours`
  * @param {number} [options.effort=7] - CPU effort, between 1 (fastest) and 10 (slowest)
@@ -557,6 +561,11 @@ function webp (options) {
  */
 function gif (options) {
   if (is.object(options)) {
+    if (is.defined(options.reoptimise)) {
+      this._setBooleanOption('gifReoptimise', options.reoptimise);
+    } else if (is.defined(options.reoptimize)) {
+      this._setBooleanOption('gifReoptimise', options.reoptimize);
+    }
     const colours = options.colours || options.colors;
     if (is.defined(colours)) {
       if (is.integer(colours) && is.inRange(colours, 2, 256)) {

src/pipeline.cc

@@ -888,6 +888,7 @@ class PipelineWorker : public Napi::AsyncWorker {
             ->set("strip", !baton->withMetadata)
             ->set("bitdepth", baton->gifBitdepth)
             ->set("effort", baton->gifEffort)
+            ->set("reoptimise", baton->gifReoptimise)
             ->set("dither", baton->gifDither)));
           baton->bufferOut = static_cast<char*>(area->data);
           baton->bufferOutLength = area->length;
@@ -1053,6 +1054,7 @@ class PipelineWorker : public Napi::AsyncWorker {
             ->set("strip", !baton->withMetadata)
             ->set("bitdepth", baton->gifBitdepth)
             ->set("effort", baton->gifEffort)
+            ->set("reoptimise", baton->gifReoptimise)
             ->set("dither", baton->gifDither));
           baton->formatOut = "gif";
         } else if (baton->formatOut == "tiff" || (mightMatchInput && isTiff) ||
@@ -1537,6 +1539,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->gifBitdepth = sharp::AttrAsUint32(options, "gifBitdepth");
   baton->gifEffort = sharp::AttrAsUint32(options, "gifEffort");
   baton->gifDither = sharp::AttrAsDouble(options, "gifDither");
+  baton->gifReoptimise = sharp::AttrAsBool(options, "gifReoptimise");
   baton->tiffQuality = sharp::AttrAsUint32(options, "tiffQuality");
   baton->tiffPyramid = sharp::AttrAsBool(options, "tiffPyramid");
   baton->tiffBitdepth = sharp::AttrAsUint32(options, "tiffBitdepth");

src/pipeline.h

@@ -162,6 +162,7 @@ struct PipelineBaton {
   int gifBitdepth;
   int gifEffort;
   double gifDither;
+  bool gifReoptimise;
   int tiffQuality;
   VipsForeignTiffCompression tiffCompression;
   VipsForeignTiffPredictor tiffPredictor;
@@ -306,6 +307,10 @@ struct PipelineBaton {
     webpEffort(4),
     webpMinSize(false),
     webpMixed(false),
+    gifBitdepth(8),
+    gifEffort(7),
+    gifDither(1.0),
+    gifReoptimise(false),
     tiffQuality(80),
     tiffCompression(VIPS_FOREIGN_TIFF_COMPRESSION_JPEG),
     tiffPredictor(VIPS_FOREIGN_TIFF_PREDICTOR_HORIZONTAL),

test/unit/gif.js

@@ -80,6 +80,22 @@ describe('GIF input', () => {
     assert.strictEqual(true, reduced.length < original.length);
   });
 
+  it('valid optimise', () => {
+    assert.doesNotThrow(() => sharp().gif({ reoptimise: true }));
+    assert.doesNotThrow(() => sharp().gif({ reoptimize: true }));
+  });
+
+  it('invalid reoptimise throws', () => {
+    assert.throws(
+      () => sharp().gif({ reoptimise: -1 }),
+      /Expected boolean for gifReoptimise but received -1 of type number/
+    );
+    assert.throws(
+      () => sharp().gif({ reoptimize: 'fail' }),
+      /Expected boolean for gifReoptimise but received fail of type string/
+    );
+  });
+
   it('invalid loop throws', () => {
     assert.throws(() => {
       sharp().gif({ loop: -1 });