Add support for withoutReduction operation.

Do this both for the sharp engine as of the support for it introduced
in 0.30.0 as well as emulation glue to gm which uses resize with '<'.

src/engines/gm.js

@@ -10,6 +10,7 @@ function createGmOperations(pipeline, operations) {
   let resize;
   let crop;
   let withoutEnlargement;
+  let withoutReduction;
   let ignoreAspectRatio;
 
   for (const requestedOperation of operations) {
@@ -22,6 +23,9 @@ function createGmOperations(pipeline, operations) {
     } else if (operation.name === 'withoutEnlargement') {
       withoutEnlargement = operation;
       continue;
+    } else if (operation.name === 'withoutReduction') {
+      withoutReduction = operation;
+      continue;
     } else if (operation.name === 'ignoreAspectRatio') {
       ignoreAspectRatio = operation;
       continue;
@@ -92,6 +96,9 @@ function createGmOperations(pipeline, operations) {
   if (withoutEnlargement && resize) {
     resize.args[2] = '>';
   }
+  if (withoutReduction && resize) {
+    resize.args[2] = '<';
+  }
   if (ignoreAspectRatio && resize) {
     resize.args[2] = '!';
   }
@@ -121,6 +128,7 @@ module.exports = {
         'extract',
         'progressive',
         'withoutEnlargement',
+        'withoutReduction',
         'ignoreAspectRatio',
       ].concat(
         Object.keys(gm.prototype).filter(
@@ -136,6 +144,7 @@ module.exports = {
     switch (name) {
       // Operations that emulate sharp's API:
       case 'withoutEnlargement':
+      case 'withoutReduction':
       case 'ignoreAspectRatio':
       case 'progressive':
         return args.length === 0;

src/engines/sharp.js

@@ -28,6 +28,7 @@ const optionsToOutputType = {
 };
 const optionsToResize = {
   withoutEnlargement: () => ({ withoutEnlargement: true }),
+  withoutReduction: () => ({ withoutReduction: true }),
   ignoreAspectRatio: () => ({ fit: 'fill' }),
 };
 const variationsToResize = {
@@ -53,6 +54,7 @@ module.exports = {
     'flip',
     'flop',
     'withoutEnlargement',
+    'withoutReduction',
     'ignoreAspectRatio',
     'blur',
     'sharpen',

test/impro.spec.js

@@ -949,6 +949,29 @@ describe('impro', () => {
       ]);
     });
 
+    it('should throw on withoutReduction without resize', () =>
+      expect(
+        () => {
+          impro.withoutReduction().flush();
+        },
+        'to throw',
+        'sharp: withoutReduction() operation must follow resize'
+      ));
+
+    it('should support withoutReduction', () => {
+      return expect(
+        'turtle.jpg',
+        'when piped through',
+        impro.resize(10, 10).withoutReduction(),
+        'to yield output satisfying',
+        'to have metadata satisfying',
+        {
+          format: 'JPEG',
+          size: { width: 481, height: 424 }, // unchanged
+        }
+      );
+    });
+
     it('should throw on ignoreAspectRatio without resize', () =>
       expect(
         () => {
@@ -1258,6 +1281,16 @@ describe('impro', () => {
       ]);
     });
 
+    it('should support withoutReduction', () => {
+      const executeSpy = sinon.spy(impro.engineByName.gm, 'execute');
+
+      impro.gm().resize(10, 10).withoutReduction().flush();
+
+      return expect(executeSpy.returnValues[0], 'to equal', [
+        { name: 'resize', args: [10, 10, '<'] },
+      ]);
+    });
+
     it('should support ignoreAspectRatio', () => {
       const executeSpy = sinon.spy(impro.engineByName.gm, 'execute');
 
@@ -1293,6 +1326,22 @@ describe('impro', () => {
       });
     });
 
+    describe('with executed conversions', () => {
+      it('should support withoutReduction', () => {
+        return expect(
+          'turtle.jpg',
+          'when piped through',
+          impro.gm().resize(10, 10).withoutReduction(),
+          'to yield output satisfying',
+          'to have metadata satisfying',
+          {
+            format: 'JPEG',
+            size: { width: 481, height: 424 }, // unchanged
+          }
+        );
+      });
+    });
+
     describe('with a maxOutputPixels setting in place', () => {
       it('should support resize (only width)', () => {
         const executeSpy = sinon.spy(impro.engineByName.gm, 'execute');