melody-rain opened a new issue #7398: inconsistent results when infering
URL: https://github.com/apache/incubator-mxnet/issues/7398
 
 
   I trained a model with VGG16 on a dataset with accuracy of 96% on the 
validation set. However when I infer with the model I trained on the same 
validation set image by image and calculate the accuracy, I got 87%, which is 
quite smaller than 96%.
   
   You know when training we make the dataset in .rec format, and for inference 
we read the image with cv2.imread().
   
   What might be the reasons that I cannot get the same accuracy? All images 
have been resized to (224, 224) and subtracted by the mean.
   
   FYI:
   ```
   96%: mod.forward(batch, is_train=False), batch is from ImageRecordIter
   87%: prob = mod.forward(Batch([mx.nd.array(img)])), img is from cv2.imread()
   ```
   
   image preprocessing to get 96%
   ```
       data = mx.io.ImageRecordIter(
           data_name          = 'data',
           label_name         = 'softmax_label',
           path_imgrec        = data_val,
           label_width        = 1,
           data_shape         = data_shape,
           preprocess_threads = data_nthreads,
           batch_size         = batch_size,
           mean_r             = rgb_mean[0],
           mean_g             = rgb_mean[1],
           mean_b             = rgb_mean[2],
           )
   ```
   
   image preprocessing to get 87%
   ```
   def get_image(file_name):
       img = cv2.cvtColor(cv2.imread(file_name), cv2.COLOR_BGR2RGB)
       if img is None:
            return None
   
       # convert into format (batch, RGB, width, height)
       img = cv2.resize(img, (224, 224))
       img = np.swapaxes(img, 0, 2)
       img = np.swapaxes(img, 1, 2)
       img = img.astype(np.float32)
       img -= mean_img
       img = img[np.newaxis, :]
       return img
   
   ```
   
   Thanks.
   
   
   
   
 
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