materials for object detection

https://github.com/fizyr/keras-retinanet
https://hackernoon.com/visualizing-parts-of-convolutional-neural-networks-using-keras-and-cats-5cc01b214e59

https://www.researchgate.net/post/In_Keras_How_can_I_extract_the_exact_location_of_the_detected_object_or_objects_within_image_that_includes_a_background
https://github.com/endernewton/tf-faster-rcnn