Ensure background metadata can be parsed #4090

docs/api-input.md

@@ -31,7 +31,7 @@ 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
+- `background`: Default background colour, if present, for PNG (bKGD) and GIF images
 - `compression`: The encoder used to compress an HEIF file, `av1` (AVIF) or `hevc` (HEIC)
 - `resolutionUnit`: The unit of resolution (density), either `inch` or `cm`, if present
 - `hasProfile`: Boolean indicating the presence of an embedded ICC profile

docs/changelog.md

@@ -10,6 +10,9 @@ Requires libvips v8.16.0-rc2
 
 * Expose WebP `smartDeblock` output option.
 
+* Ensure `background` metadata can be parsed by `color` package.
+  [#4090](https://github.com/lovell/sharp/issues/4090)
+
 * TypeScript: Ensure channel counts use the correct range.
   [#4197](https://github.com/lovell/sharp/pull/4197)
   [@DavidVaness](https://github.com/DavidVaness)

lib/index.d.ts

@@ -1106,8 +1106,8 @@ declare namespace sharp {
         tifftagPhotoshop?: Buffer | undefined;
         /** The encoder used to compress an HEIF file, `av1` (AVIF) or `hevc` (HEIC) */
         compression?: 'av1' | 'hevc';
-        /** Default background colour, if present, for PNG (bKGD) and GIF images, either an RGB Object or a single greyscale value */
+        /** Default background colour, if present, for PNG (bKGD) and GIF images */
-        background?: { r: number; g: number; b: number } | number;
+        background?: { r: number; g: number; b: number } | { gray: number };
         /** Details of each level in a multi-level image provided as an array of objects, requires libvips compiled with support for OpenSlide */
         levels?: LevelMetadata[] | undefined;
         /** Number of Sub Image File Directories in an OME-TIFF image */

lib/input.js

@@ -443,7 +443,7 @@ 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
+ * - `background`: Default background colour, if present, for PNG (bKGD) and GIF images
  * - `compression`: The encoder used to compress an HEIF file, `av1` (AVIF) or `hevc` (HEIC)
  * - `resolutionUnit`: The unit of resolution (density), either `inch` or `cm`, if present
  * - `hasProfile`: Boolean indicating the presence of an embedded ICC profile

src/metadata.cc

@@ -3,6 +3,7 @@
 
 #include <numeric>
 #include <vector>
+#include <cmath>
 
 #include <napi.h>
 #include <vips/vips8>
@@ -226,15 +227,15 @@ class MetadataWorker : public Napi::AsyncWorker {
         info.Set("subifds", baton->subifds);
       }
       if (!baton->background.empty()) {
-        if (baton->background.size() == 3) {
         Napi::Object background = Napi::Object::New(env);
+        if (baton->background.size() == 3) {
           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]);
+          background.Set("gray", round(baton->background[0] * 100 / 255));
         }
+        info.Set("background", background);
       }
       info.Set("hasProfile", baton->hasProfile);
       info.Set("hasAlpha", baton->hasAlpha);

test/fixtures/index.js

@@ -80,6 +80,8 @@ module.exports = {
   inputPngWithGreyAlpha: getPath('grey-8bit-alpha.png'),
   inputPngWithOneColor: getPath('2x2_fdcce6.png'),
   inputPngWithTransparency16bit: getPath('tbgn2c16.png'), // http://www.schaik.com/pngsuite/tbgn2c16.png
+  inputPng8BitGreyBackground: getPath('bgbn4a08.png'), // http://www.schaik.com/pngsuite/bgbn4a08.png
+  inputPng16BitGreyBackground: getPath('bggn4a16.png'), // http://www.schaik.com/pngsuite/bggn4a16.png
   inputPng16BitGreyAlpha: getPath('16-bit-grey-alpha.png'), // CC-BY-NC-SA florc http://www.colourlovers.com/pattern/50713/pat
   inputPngOverlayLayer0: getPath('alpha-layer-0-background.png'),
   inputPngOverlayLayer1: getPath('alpha-layer-1-fill.png'),

test/unit/metadata.js

@@ -201,6 +201,48 @@ describe('Image metadata', function () {
     });
   });
 
+  it('PNG with greyscale bKGD chunk - 8 bit', async () => {
+    const data = await sharp(fixtures.inputPng8BitGreyBackground).metadata();
+    assert.deepStrictEqual(data, {
+      background: {
+        gray: 0
+      },
+      bitsPerSample: 8,
+      channels: 2,
+      density: 72,
+      depth: 'uchar',
+      format: 'png',
+      hasAlpha: true,
+      hasProfile: false,
+      height: 32,
+      isPalette: false,
+      isProgressive: false,
+      space: 'b-w',
+      width: 32
+    });
+  });
+
+  it('PNG with greyscale bKGD chunk - 16 bit', async () => {
+    const data = await sharp(fixtures.inputPng16BitGreyBackground).metadata();
+    assert.deepStrictEqual(data, {
+      background: {
+        gray: 67
+      },
+      bitsPerSample: 16,
+      channels: 2,
+      density: 72,
+      depth: 'ushort',
+      format: 'png',
+      hasAlpha: true,
+      hasProfile: false,
+      height: 32,
+      isPalette: false,
+      isProgressive: false,
+      space: 'grey16',
+      width: 32
+    });
+  });
+
   it('WebP', function (done) {
     sharp(fixtures.inputWebP).metadata(function (err, metadata) {
       if (err) throw err;