piiswrong commented on a change in pull request #7345: add std_rgba to 
normalize options
URL: https://github.com/apache/incubator-mxnet/pull/7345#discussion_r132511245
 
 

 ##########
 File path: src/io/iter_normalize.h
 ##########
 @@ -129,33 +129,58 @@ class ImageNormalizeIter : public IIterator<DataInst> {
     if (param_.mean_r > 0.0f || param_.mean_g > 0.0f ||
         param_.mean_b > 0.0f || param_.mean_a > 0.0f) {
       // subtract mean per channel
-      data[0] -= param_.mean_r;
-      if (data.shape_[0] >= 3) {
-        data[1] -= param_.mean_g;
-        data[2] -= param_.mean_b;
-      }
-      if (data.shape_[0] == 4) {
-        data[3] -= param_.mean_a;
-      }
-      if ((param_.rand_mirror && coin_flip(rnd_)) || param_.mirror) {
-        outimg_ = mirror(data * contrast + illumination) * param_.scale;
-      } else {
-        outimg_ = (data * contrast + illumination) * param_.scale;
+      switch (data.shape_[0]) {
+        case 4: {
+          data[3] -= param_.mean_a;
+        }
+        case 3: {
+          data[2] -= param_.mean_b;
+        }
+        case 2: {
+          data[1] -= param_.mean_g;
+        }
+        case 1: {
+          data[0] -= param_.mean_r;
+          break;
+        }
+        default: {
+          // possible?
+        }
       }
     } else if (!meanfile_ready_ || param_.mean_img.length() == 0) {
       // do not subtract anything
-      if ((param_.rand_mirror && coin_flip(rnd_)) || param_.mirror) {
-        outimg_ = mirror(data) * param_.scale;
-      } else {
-        outimg_ = F<mshadow::op::identity>(data) * param_.scale;
-      }
     } else {
       CHECK(meanfile_ready_);
-      if ((param_.rand_mirror && coin_flip(rnd_)) || param_.mirror) {
-        outimg_ = mirror((data - meanimg_) * contrast + illumination) * 
param_.scale;
-      } else {
-        outimg_ = ((data - meanimg_) * contrast + illumination) * param_.scale;
+      data -= meanimg_;
+    }
+    // apply contrast and illumination jitter
+    data = data * contrast + illumination;
+    // apply std per channel
+    switch (data.shape_[0]) {
+      case 4: {
+        if (param_.std_a > 0.0f) data[3] /= param_.std_a;
       }
+      case 3: {
+        if (param_.std_b > 0.0f) data[2] /= param_.std_b;
+      }
+      case 2: {
+        if (param_.std_g > 0.0f) data[1] /= param_.std_g;
+      }
+      case 1: {
+        if (param_.std_r > 0.0f) data[0] /= param_.std_r;
+        break;
+      }
+      default: {
+        // possible?
+      }
+    }
+    // scale the values globally
+    data *= param_.scale;
 
 Review comment:
   The computation was condensed in one line because its faster that way.
   
   Are you sure contrast and illumination should happen after std?
 
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