Add default background metadata for PNG and GIF images

docs/api-input.md

@@ -22,6 +22,7 @@ A `Promise` is returned when `callback` is not provided.
 *   `pagePrimary`: Number of the primary page in a HEIF image
 *   `levels`: Details of each level in a multi-level image provided as an array of objects, requires libvips compiled with support for OpenSlide
 *   `subifds`: Number of Sub Image File Directories in an OME-TIFF image
+*   `background`: Default background colour, if present, for PNG (bKGD) and GIF images, either an RGB Object or a single greyscale value
 *   `compression`: The encoder used to compress an HEIF file, `av1` (AVIF) or `hevc` (HEIC)
 *   `hasProfile`: Boolean indicating the presence of an embedded ICC profile
 *   `hasAlpha`: Boolean indicating the presence of an alpha transparency channel

docs/changelog.md

@@ -8,6 +8,8 @@ Requires libvips v8.11.2
 
 * Drop support for Node.js 10, now requires Node.js >= 12.13.0.
 
+* Add `background` property to PNG and GIF image metadata.
+
 * Add `compression` property to HEIF image metadata.
   [#2504](https://github.com/lovell/sharp/issues/2504)
 

lib/input.js

@@ -271,6 +271,7 @@ function _isStreamInput () {
  * - `pagePrimary`: Number of the primary page in a HEIF image
  * - `levels`: Details of each level in a multi-level image provided as an array of objects, requires libvips compiled with support for OpenSlide
  * - `subifds`: Number of Sub Image File Directories in an OME-TIFF image
+ * - `background`: Default background colour, if present, for PNG (bKGD) and GIF images, either an RGB Object or a single greyscale value
  * - `compression`: The encoder used to compress an HEIF file, `av1` (AVIF) or `hevc` (HEIC)
  * - `hasProfile`: Boolean indicating the presence of an embedded ICC profile
  * - `hasAlpha`: Boolean indicating the presence of an alpha transparency channel

src/metadata.cc

@@ -90,6 +90,9 @@ class MetadataWorker : public Napi::AsyncWorker {
         baton->subifds = image.get_int(VIPS_META_N_SUBIFDS);
       }
       baton->hasProfile = sharp::HasProfile(image);
+      if (image.get_typeof("background") == VIPS_TYPE_ARRAY_DOUBLE) {
+        baton->background = image.get_array_double("background");
+      }
       // Derived attributes
       baton->hasAlpha = sharp::HasAlpha(image);
       baton->orientation = sharp::ExifOrientation(image);
@@ -209,6 +212,17 @@ class MetadataWorker : public Napi::AsyncWorker {
       if (baton->subifds > 0) {
         info.Set("subifds", baton->subifds);
       }
+      if (!baton->background.empty()) {
+        if (baton->background.size() == 3) {
+          Napi::Object background = Napi::Object::New(env);
+          background.Set("r", baton->background[0]);
+          background.Set("g", baton->background[1]);
+          background.Set("b", baton->background[2]);
+          info.Set("background", background);
+        } else {
+          info.Set("background", baton->background[0]);
+        }
+      }
       info.Set("hasProfile", baton->hasProfile);
       info.Set("hasAlpha", baton->hasAlpha);
       if (baton->orientation > 0) {

src/metadata.h

@@ -42,6 +42,7 @@ struct MetadataBaton {
   std::string compression;
   std::vector<std::pair<int, int>> levels;
   int subifds;
+  std::vector<double> background;
   bool hasProfile;
   bool hasAlpha;
   int orientation;

test/unit/metadata.js

@@ -256,6 +256,7 @@ describe('Image metadata', function () {
       assert.strictEqual('undefined', typeof metadata.orientation);
       assert.strictEqual('undefined', typeof metadata.exif);
       assert.strictEqual('undefined', typeof metadata.icc);
+      assert.deepStrictEqual(metadata.background, { r: 138, g: 148, b: 102 });
       done();
     });
   });
@@ -285,7 +286,7 @@ describe('Image metadata', function () {
       .then(({
         format, width, height, space, channels, depth,
         isProgressive, pages, pageHeight, loop, delay,
-        hasProfile, hasAlpha
+        background, hasProfile, hasAlpha
       }) => {
         assert.strictEqual(format, 'gif');
         assert.strictEqual(width, 80);
@@ -298,6 +299,7 @@ describe('Image metadata', function () {
         assert.strictEqual(pageHeight, 80);
         assert.strictEqual(loop, 0);
         assert.deepStrictEqual(delay, Array(30).fill(30));
+        assert.deepStrictEqual(background, { r: 0, g: 0, b: 0 });
         assert.strictEqual(hasProfile, false);
         assert.strictEqual(hasAlpha, true);
       })