[image classifier ] Fix memory leak in image classifier (#697)

* uses tidy to fix mem leak in imageClassifier

* sends in raw image vs tensor to predict

* send in processed tensor to classify

Author: joeyklee

src/ImageClassifier/index.js

@@ -130,7 +130,7 @@ class ImageClassifier {
    * @return {object} an object with {label, confidence}.
    */
   async classifyInternal(imgToPredict, numberOfClasses) {
-
+    
     // Wait for the model to be ready
     await this.ready;
     await tf.nextFrame();
@@ -152,14 +152,15 @@ class ImageClassifier {
 
     // Process the images
     const imageResize = [IMAGE_SIZE, IMAGE_SIZE];
-    const processedImg = imgToTensor(imgToPredict, imageResize);
-
+    
     if (this.modelUrl) {
       await tf.nextFrame();
       const predictedClasses = tf.tidy(() => {
+        const processedImg = imgToTensor(imgToPredict, imageResize);
         const predictions = this.model.predict(processedImg);
         return Array.from(predictions.as1D().dataSync());
       });
+      
       const results = await predictedClasses.map((confidence, index) => {
         const label = (this.mapStringToIndex.length > 0 && this.mapStringToIndex[index]) ? this.mapStringToIndex[index] : index;
         return {
@@ -168,15 +169,16 @@ class ImageClassifier {
         };
       }).sort((a, b) => b.confidence - a.confidence);
       return results;
-    }
+    } 
 
-    const result = this.model
+    const processedImg = imgToTensor(imgToPredict, imageResize);
+    const results = this.model
       .classify(processedImg, numberOfClasses)
       .then(classes => classes.map(c => ({ label: c.className, confidence: c.probability })));
 
     processedImg.dispose();
-
-    return result;
+    
+    return results;
   }
 
   /**