Add withGainMap to process HDR JPEGs with embedded gain map #4314

test/fixtures/index.js

@@ -70,6 +70,7 @@ module.exports = {
   inputJpgRandom: getPath('random.jpg'), // convert -size 200x200 xc:   +noise Random   random.jpg
   inputJpgThRandom: getPath('thRandom.jpg'), // convert random.jpg  -channel G -threshold 5% -separate +channel -negate thRandom.jpg
   inputJpgLossless: getPath('testimgl.jpg'), // Lossless JPEG from ftp://ftp.fu-berlin.de/unix/X11/graphics/ImageMagick/delegates/ljpeg-6b.tar.gz
+  inputJpgWithGainMap: getPath('gain-map.jpg'), // https://github.com/libvips/libvips/issues/3799
 
   inputPng: getPath('50020484-00001.png'), // http://c.searspartsdirect.com/lis_png/PLDM/50020484-00001.png
   inputPngGradients: getPath('gradients-rgb8.png'),

test/unit/gain-map.js

@@ -0,0 +1,69 @@
+/*!
+  Copyright 2013 Lovell Fuller and others.
+  SPDX-License-Identifier: Apache-2.0
+*/
+
+const { describe, it } = require('node:test');
+
+const sharp = require('../../');
+const fixtures = require('../fixtures');
+
+describe('Gain maps', () => {
+  it('Metadata contains gainMap', async (t) => {
+    t.plan(4);
+
+    const { format, gainMap } = await sharp(
+      fixtures.inputJpgWithGainMap,
+    ).metadata();
+    t.assert.strictEqual(format, 'jpeg');
+    t.assert.strictEqual(typeof gainMap, 'object');
+    t.assert.ok(Buffer.isBuffer(gainMap.image));
+    t.assert.strictEqual(gainMap.image.length, 31738);
+  });
+
+  it('Can be regenerated', async (t) => {
+    t.plan(4);
+
+    const data = await sharp(fixtures.inputJpgWithGainMap)
+      .withGainMap()
+      .toBuffer();
+    const metadata = await sharp(data).metadata();
+    t.assert.strictEqual(metadata.format, 'jpeg');
+    t.assert.strictEqual(typeof metadata.gainMap, 'object');
+    t.assert.ok(Buffer.isBuffer(metadata.gainMap.image));
+
+    const {
+      format,
+      width,
+      height,
+      channels,
+      depth,
+      space,
+      hasProfile,
+      chromaSubsampling,
+    } = await sharp(metadata.gainMap.image).metadata();
+
+    t.assert.deepEqual(
+      {
+        format,
+        width,
+        height,
+        channels,
+        depth,
+        space,
+        hasProfile,
+        chromaSubsampling,
+      },
+      {
+        format: 'jpeg',
+        width: 1920,
+        height: 1080,
+        channels: 1,
+        depth: 'uchar',
+        space: 'b-w',
+        hasProfile: true,
+        chromaSubsampling: '4:4:4',
+      },
+    );
+  });
+});