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

lib/output.js

@@ -319,6 +319,30 @@ function withIccProfile (icc, options) {
   return this;
 }
 
+/**
+ * If the input contains gain map metadata, use it to convert the main image to HDR (High Dynamic Range) before further processing.
+ * The input gain map is discarded.
+ *
+ * If the output is JPEG, generate and attach a new ISO 21496-1 gain map.
+ * JPEG output options other than `quality` are ignored.
+ *
+ * This feature is experimental and the API may change.
+ *
+ * @since 0.35.0
+ *
+ * @example
+ * const outputWithGainMap = await sharp(inputWithGainMap)
+ *   .withGainMap()
+ *   .toBuffer();
+ *
+ * @returns {Sharp}
+ */
+function withGainMap() {
+  this.options.withGainMap = true;
+  this.options.colourspace = 'scrgb';
+  return this;
+}
+
 /**
  * Keep XMP metadata from the input image in the output image.
  *
@@ -1640,6 +1664,7 @@ module.exports = (Sharp) => {
     withExifMerge,
     keepIccProfile,
     withIccProfile,
+    withGainMap,
     keepXmp,
     withXmp,
     keepMetadata,