问题
I've been learning Keras recently and I tried my hand at the CIFAR10 dataset with CNNs. However, the model I trained (you can run the code here) returns the same answer for every input, no matter what. Did I forget something in the model definition?
回答1:
You have forgotten to normalize the images. Currently, the values in x_train are in the range [0,255]. This causes large gradient updates and stalls training process. One simple normalization scheme in this case would be:
x_train = x_train.astype('float32') / 255
x_test = x_test.astype('float32') / 255
This causes the values to fall in the range [0,1]. Then you would surely see that the training progresses.
A more sophisticated normalization scheme involves feature-wise (i.e. pixel-wise) normalization or centering. In this approach we normalize all the images such that each pixel in all the images have a mean of zero and a standard deviation of one (i.e. they mostly fall in the range [-1,1]):
# make sure values are float
x_train = x_train.astype('float32')
x_test = x_test.astype('float32')
x_mean = x_train.mean(axis=0)
x_train -= x_mean
x_std = x_train.std(axis=0)
x_train /= x_std + 1e-8 # add a small constant to prevent division by zero
# normalize test data using the mean and std of training data
x_test -= x_mean
x_test /= x_std + 1e-8
Note the last part: NEVER EVER normalize test data by its own mean and std. Use the training mean and std instead.
回答2:
you are doing prediction on x_test
predictions = model.predict_classes(x_test, batch_size=50)
and than comparing them with y_train
comparison = [(predictions[i], y_train_[i][0]) for i in range(0, len(predictions))]
I think it should be y_test
来源：https://stackoverflow.com/questions/51117763/cnns-on-keras-converge-to-the-same-value-no-matter-the-input