Add resolutionUnit to metadata and as tiff option #3023

Co-authored-by: Lovell Fuller <github@lovell.info>

lib/constructor.js

@@ -262,6 +262,7 @@ const Sharp = function (input, options) {
     tiffTileWidth: 256,
     tiffXres: 1.0,
     tiffYres: 1.0,
+    tiffResolutionUnit: 'inch',
     heifQuality: 50,
     heifLossless: false,
     heifCompression: 'av1',

lib/output.js

@@ -704,6 +704,7 @@ function trySetAnimationOptions (source, target) {
  * @param {number} [options.tileHeight=256] - vertical tile size
  * @param {number} [options.xres=1.0] - horizontal resolution in pixels/mm
  * @param {number} [options.yres=1.0] - vertical resolution in pixels/mm
+ * @param {string} [options.resolutionUnit='inch'] - resolution unit options: inch, cm
  * @param {number} [options.bitdepth=8] - reduce bitdepth to 1, 2 or 4 bit
  * @returns {Sharp}
  * @throws {Error} Invalid options
@@ -777,6 +778,14 @@ function tiff (options) {
         throw is.invalidParameterError('predictor', 'one of: none, horizontal, float', options.predictor);
       }
     }
+    // resolutionUnit
+    if (is.defined(options.resolutionUnit)) {
+      if (is.string(options.resolutionUnit) && is.inArray(options.resolutionUnit, ['inch', 'cm'])) {
+        this.options.tiffResolutionUnit = options.resolutionUnit;
+      } else {
+        throw is.invalidParameterError('resolutionUnit', 'one of: inch, cm', options.resolutionUnit);
+      }
+    }
   }
   return this._updateFormatOut('tiff', options);
 }