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I recently upgraded my Colab instance to TensorFlow 2.0 and have attempted to train a Sequential Classification model on a batch of PNG images. I have used the !tf_upgrade_v2 command listed on tensorflow.org to upgrade the script from TensorFlow 1.14 to 2.0 format.

When I attempt to train the model using model.fit_generator code below I get a re-occurring non-fatal UserWarning line after line as the model runs through each epoch. 

# Train the model
history = model.fit_generator(
    train_generator,
    steps_per_epoch=nb_train_samples // batch_size,
    epochs=epochs,
    validation_data=validation_generator,
    validation_steps=nb_validation_samples // batch_size)

An example of the warning is:

1/449 [..............................] - ETA: 12:04 - loss: 3.0403 - accuracy: 0.1250
/usr/local/lib/python3.6/dist-packages/PIL/Image.py:914: UserWarning: Palette images 
with Transparency expressed in bytes should be converted to RGBA images to RGBA
images')

This warning did not appear when using TensorFlow 1.14 when trained on the same batch of PNG images. The TF2.0 model does continue to train, however it is slowing the training process significantly as it keeps printing to the warning.

I have gone back to the dataset and tried converting the PNGs ensuring that they are in RGB format not RGBA using the example listed here however this has failed to resolve the problem.

EQNX
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  • I amot sure if this helps or not but RGBA is something and RGB is another, RGBA is an image composed of 4 channels Red, Green, Blue, Alpha, and the other dont have the alpha channel. What is the Alpha Channel? this is the channel responsible for the opacity of the image. Apart from that, given the warning it is a user warning nothing much to be afraid of IMHO, if it works with TF 1.14 normally then give the TF2.0 and this warning wont be there. I hope I added something to you, – ElSheikh Nov 07 '19 at 20:12

1 Answers1

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After further research I found further details about the ImageDataGenerator and specifically the flow_from_dataframe method in the TensorFlow Core r2.0 documentation.

The UserWarning described can be resolved by adding the color_mode='rgba' parameter to the flow_from_dataframe method.

For example:

from tensorflow.python.keras.preprocessing.image import ImageDataGenerator

train_datagen = ImageDataGenerator(
    rotation_range=10,
    width_shift_range=0.1,
    height_shift_range=0.1,
    rescale=1. / 255,
    shear_range=0.1,
    zoom_range=0.2,
    horizontal_flip=False,
    fill_mode='nearest')

train_generator = train_datagen.flow_from_directory(
    train_data_dir,
    target_size=(150, 150),
    batch_size=16,
    save_format='png',
    class_mode='sparse',
    color_mode='rgba')
EQNX
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