frontend.py

from keras.models import Model
from keras.layers import Reshape, Activation, Conv2D, Input, MaxPooling2D, BatchNormalization, Flatten, Dense, Lambda
from keras.layers.advanced_activations import LeakyReLU
import tensorflow as tf
import numpy as np
import os
import cv2
from keras.applications.mobilenet import MobileNet
from keras.layers.merge import concatenate
from keras.optimizers import SGD, Adam, RMSprop
from preprocessing import BatchGenerator
from keras.callbacks import EarlyStopping, ModelCheckpoint, TensorBoard
from utils import BoundBox
from backend import TinyYoloFeature, FullYoloFeature, MobileNetFeature, SqueezeNetFeature, Inception3Feature, VGG16Feature, ResNet50Feature

class YOLO(object):
    def __init__(self, architecture,
                       input_size, 
                       labels, 
                       max_box_per_image,
                       anchors):

        self.input_size = input_size
        
        self.labels   = list(labels)
        self.nb_class = len(self.labels)
        self.nb_box   = len(anchors)/2
        self.class_wt = np.ones(self.nb_class, dtype='float32')
        self.anchors  = anchors

        self.max_box_per_image = max_box_per_image

        ##########################
        # Make the model
        ##########################

        # make the feature extractor layers
        input_image     = Input(shape=(self.input_size, self.input_size, 3))
        self.true_boxes = Input(shape=(1, 1, 1, max_box_per_image , 4))  

        if architecture == 'Inception3':
            self.feature_extractor = Inception3Feature(self.input_size)  
        elif architecture == 'SqueezeNet':
            self.feature_extractor = SqueezeNetFeature(self.input_size)        
        elif architecture == 'MobileNet':
            self.feature_extractor = MobileNetFeature(self.input_size)
        elif architecture == 'Full Yolo':
            self.feature_extractor = FullYoloFeature(self.input_size)
        elif architecture == 'Tiny Yolo':
            self.feature_extractor = TinyYoloFeature(self.input_size)
        elif architecture == 'VGG16':
            self.feature_extractor = VGG16Feature(self.input_size)
        elif architecture == 'ResNet50':
            self.feature_extractor = ResNet50Feature(self.input_size)
        else:
            raise Exception('Architecture not supported! Only support Full Yolo, Tiny Yolo, MobileNet, SqueezeNet, VGG16, ResNet50, and Inception3 at the moment!')

        print self.feature_extractor.get_output_shape()    
        self.grid_h, self.grid_w = self.feature_extractor.get_output_shape()        
        features = self.feature_extractor.extract(input_image)            

        # make the object detection layer
        output = Conv2D(self.nb_box * (4 + 1 + self.nb_class), 
                        (1,1), strides=(1,1), 
                        padding='same', 
                        name='conv_23', 
                        kernel_initializer='lecun_normal')(features)
        output = Reshape((self.grid_h, self.grid_w, self.nb_box, 4 + 1 + self.nb_class))(output)
        output = Lambda(lambda args: args[0])([output, self.true_boxes])

        self.model = Model([input_image, self.true_boxes], output)
        
        # initialize the weights of the detection layer
        layer = self.model.layers[-4]
        weights = layer.get_weights()

        new_kernel = np.random.normal(size=weights[0].shape)/(self.grid_h*self.grid_w)
        new_bias   = np.random.normal(size=weights[1].shape)/(self.grid_h*self.grid_w)

        layer.set_weights([new_kernel, new_bias])

        # print a summary of the whole model
        self.model.summary()

    def custom_loss(self, y_true, y_pred):
        mask_shape = tf.shape(y_true)[:4]
        
        cell_x = tf.to_float(tf.reshape(tf.tile(tf.range(self.grid_w), [self.grid_h]), (1, self.grid_h, self.grid_w, 1, 1)))
        cell_y = tf.transpose(cell_x, (0,2,1,3,4))

        cell_grid = tf.tile(tf.concat([cell_x,cell_y], -1), [self.batch_size, 1, 1, self.nb_box, 1])
        
        coord_mask = tf.zeros(mask_shape)
        conf_mask  = tf.zeros(mask_shape)
        class_mask = tf.zeros(mask_shape)
        
        seen = tf.Variable(0.)
        total_recall = tf.Variable(0.)
        
        """
        Adjust prediction
        """
        ### adjust x and y      
        pred_box_xy = tf.sigmoid(y_pred[..., :2]) + cell_grid
        
        ### adjust w and h
        pred_box_wh = tf.exp(y_pred[..., 2:4]) * np.reshape(self.anchors, [1,1,1,self.nb_box,2])
        
        ### adjust confidence
        pred_box_conf = tf.sigmoid(y_pred[..., 4])
        
        ### adjust class probabilities
        pred_box_class = y_pred[..., 5:]
        
        """
        Adjust ground truth
        """
        ### adjust x and y
        true_box_xy = y_true[..., 0:2] # relative position to the containing cell
        
        ### adjust w and h
        true_box_wh = y_true[..., 2:4] # number of cells accross, horizontally and vertically
        
        ### adjust confidence
        true_wh_half = true_box_wh / 2.
        true_mins    = true_box_xy - true_wh_half
        true_maxes   = true_box_xy + true_wh_half
        
        pred_wh_half = pred_box_wh / 2.
        pred_mins    = pred_box_xy - pred_wh_half
        pred_maxes   = pred_box_xy + pred_wh_half       
        
        intersect_mins  = tf.maximum(pred_mins,  true_mins)
        intersect_maxes = tf.minimum(pred_maxes, true_maxes)
        intersect_wh    = tf.maximum(intersect_maxes - intersect_mins, 0.)
        intersect_areas = intersect_wh[..., 0] * intersect_wh[..., 1]
        
        true_areas = true_box_wh[..., 0] * true_box_wh[..., 1]
        pred_areas = pred_box_wh[..., 0] * pred_box_wh[..., 1]

        union_areas = pred_areas + true_areas - intersect_areas
        iou_scores  = tf.truediv(intersect_areas, union_areas)
        
        true_box_conf = iou_scores * y_true[..., 4]
        
        ### adjust class probabilities
        true_box_class = tf.argmax(y_true[..., 5:], -1)
        
        """
        Determine the masks
        """
        ### coordinate mask: simply the position of the ground truth boxes (the predictors)
        coord_mask = tf.expand_dims(y_true[..., 4], axis=-1) * self.coord_scale
        
        ### confidence mask: penelize predictors + penalize boxes with low IOU
        # penalize the confidence of the boxes, which have IOU with some ground truth box < 0.6
        true_xy = self.true_boxes[..., 0:2]
        true_wh = self.true_boxes[..., 2:4]
        
        true_wh_half = true_wh / 2.
        true_mins    = true_xy - true_wh_half
        true_maxes   = true_xy + true_wh_half
        
        pred_xy = tf.expand_dims(pred_box_xy, 4)
        pred_wh = tf.expand_dims(pred_box_wh, 4)
        
        pred_wh_half = pred_wh / 2.
        pred_mins    = pred_xy - pred_wh_half
        pred_maxes   = pred_xy + pred_wh_half    
        
        intersect_mins  = tf.maximum(pred_mins,  true_mins)
        intersect_maxes = tf.minimum(pred_maxes, true_maxes)
        intersect_wh    = tf.maximum(intersect_maxes - intersect_mins, 0.)
        intersect_areas = intersect_wh[..., 0] * intersect_wh[..., 1]
        
        true_areas = true_wh[..., 0] * true_wh[..., 1]
        pred_areas = pred_wh[..., 0] * pred_wh[..., 1]

        union_areas = pred_areas + true_areas - intersect_areas
        iou_scores  = tf.truediv(intersect_areas, union_areas)

        best_ious = tf.reduce_max(iou_scores, axis=4)
        conf_mask = conf_mask + tf.to_float(best_ious < 0.6) * (1 - y_true[..., 4]) * self.no_object_scale
        
        # penalize the confidence of the boxes, which are reponsible for corresponding ground truth box
        conf_mask = conf_mask + y_true[..., 4] * self.object_scale
        
        ### class mask: simply the position of the ground truth boxes (the predictors)
        class_mask = y_true[..., 4] * tf.gather(self.class_wt, true_box_class) * self.class_scale       
        
        """
        Warm-up training
        """
        no_boxes_mask = tf.to_float(coord_mask < self.coord_scale/2.)
        seen = tf.assign_add(seen, 1.)
        
        true_box_xy, true_box_wh, coord_mask = tf.cond(tf.less(seen, self.warmup_bs), 
                              lambda: [true_box_xy + (0.5 + cell_grid) * no_boxes_mask, 
                                       true_box_wh + tf.ones_like(true_box_wh) * np.reshape(self.anchors, [1,1,1,self.nb_box,2]) * no_boxes_mask, 
                                       tf.ones_like(coord_mask)],
                              lambda: [true_box_xy, 
                                       true_box_wh,
                                       coord_mask])
        
        """
        Finalize the loss
        """
        nb_coord_box = tf.reduce_sum(tf.to_float(coord_mask > 0.0))
        nb_conf_box  = tf.reduce_sum(tf.to_float(conf_mask  > 0.0))
        nb_class_box = tf.reduce_sum(tf.to_float(class_mask > 0.0))
        
        loss_xy    = tf.reduce_sum(tf.square(true_box_xy-pred_box_xy)     * coord_mask) / (nb_coord_box + 1e-6) / 2.
        loss_wh    = tf.reduce_sum(tf.square(true_box_wh-pred_box_wh)     * coord_mask) / (nb_coord_box + 1e-6) / 2.
        loss_conf  = tf.reduce_sum(tf.square(true_box_conf-pred_box_conf) * conf_mask)  / (nb_conf_box  + 1e-6) / 2.
        loss_class = tf.nn.sparse_softmax_cross_entropy_with_logits(labels=true_box_class, logits=pred_box_class)
        loss_class = tf.reduce_sum(loss_class * class_mask) / (nb_class_box + 1e-6)
        
        loss = loss_xy + loss_wh + loss_conf + loss_class
        
        if self.debug:
            nb_true_box = tf.reduce_sum(y_true[..., 4])
            nb_pred_box = tf.reduce_sum(tf.to_float(true_box_conf > 0.5) * tf.to_float(pred_box_conf > 0.3))
            
            current_recall = nb_pred_box/(nb_true_box + 1e-6)
            total_recall = tf.assign_add(total_recall, current_recall) 

            loss = tf.Print(loss, [tf.zeros((1))], message='Dummy Line \t', summarize=1000)
            loss = tf.Print(loss, [loss_xy], message='Loss XY \t', summarize=1000)
            loss = tf.Print(loss, [loss_wh], message='Loss WH \t', summarize=1000)
            loss = tf.Print(loss, [loss_conf], message='Loss Conf \t', summarize=1000)
            loss = tf.Print(loss, [loss_class], message='Loss Class \t', summarize=1000)
            loss = tf.Print(loss, [loss], message='Total Loss \t', summarize=1000)
            loss = tf.Print(loss, [current_recall], message='Current Recall \t', summarize=1000)
            loss = tf.Print(loss, [total_recall/seen], message='Average Recall \t', summarize=1000)
        
        return loss

    def load_weights(self, weight_path):
        self.model.load_weights(weight_path)

    def predict(self, image):
        image = cv2.resize(image, (self.input_size, self.input_size))
        image = self.feature_extractor.normalize(image)

        input_image = image[:,:,::-1]
        input_image = np.expand_dims(input_image, 0)
        dummy_array = dummy_array = np.zeros((1,1,1,1,self.max_box_per_image,4))

        netout = self.model.predict([input_image, dummy_array])[0]
        boxes  = self.decode_netout(netout)
        
        return boxes

    def bbox_iou(self, box1, box2):
        x1_min  = box1.x - box1.w/2
        x1_max  = box1.x + box1.w/2
        y1_min  = box1.y - box1.h/2
        y1_max  = box1.y + box1.h/2
        
        x2_min  = box2.x - box2.w/2
        x2_max  = box2.x + box2.w/2
        y2_min  = box2.y - box2.h/2
        y2_max  = box2.y + box2.h/2
        
        intersect_w = self.interval_overlap([x1_min, x1_max], [x2_min, x2_max])
        intersect_h = self.interval_overlap([y1_min, y1_max], [y2_min, y2_max])
        
        intersect = intersect_w * intersect_h
        
        union = box1.w * box1.h + box2.w * box2.h - intersect
        
        return float(intersect) / union
        
    def interval_overlap(self, interval_a, interval_b):
        x1, x2 = interval_a
        x3, x4 = interval_b

        if x3 < x1:
            if x4 < x1:
                return 0
            else:
                return min(x2,x4) - x1
        else:
            if x2 < x3:
                return 0
            else:
                return min(x2,x4) - x3          

    def decode_netout(self, netout, obj_threshold=0.3, nms_threshold=0.3):
        grid_h, grid_w, nb_box = netout.shape[:3]

        boxes = []
        
        # decode the output by the network
        netout[..., 4]  = self.sigmoid(netout[..., 4])
        netout[..., 5:] = netout[..., 4][..., np.newaxis] * self.softmax(netout[..., 5:])
        netout[..., 5:] *= netout[..., 5:] > obj_threshold
        
        for row in range(grid_h):
            for col in range(grid_w):
                for b in range(nb_box):
                    # from 4th element onwards are confidence and class classes
                    classes = netout[row,col,b,5:]
                    
                    if np.sum(classes) > 0:
                        # first 4 elements are x, y, w, and h
                        x, y, w, h = netout[row,col,b,:4]

                        x = (col + self.sigmoid(x)) / grid_w # center position, unit: image width
                        y = (row + self.sigmoid(y)) / grid_h # center position, unit: image height
                        w = self.anchors[2 * b + 0] * np.exp(w) / grid_w # unit: image width
                        h = self.anchors[2 * b + 1] * np.exp(h) / grid_h # unit: image height
                        confidence = netout[row,col,b,4]
                        
                        box = BoundBox(x, y, w, h, confidence, classes)
                        
                        boxes.append(box)

        # suppress non-maximal boxes
        for c in range(self.nb_class):
            sorted_indices = list(reversed(np.argsort([box.classes[c] for box in boxes])))

            for i in xrange(len(sorted_indices)):
                index_i = sorted_indices[i]
                
                if boxes[index_i].classes[c] == 0: 
                    continue
                else:
                    for j in xrange(i+1, len(sorted_indices)):
                        index_j = sorted_indices[j]
                        
                        if self.bbox_iou(boxes[index_i], boxes[index_j]) >= nms_threshold:
                            boxes[index_j].classes[c] = 0
                            
        # remove the boxes which are less likely than a obj_threshold
        boxes = [box for box in boxes if box.get_score() > obj_threshold]
        
        return boxes

    def sigmoid(self, x):
        return 1. / (1. + np.exp(-x))

    def softmax(self, x, axis=-1, t=-100.):
        x = x - np.max(x)
        
        if np.min(x) < t:
            x = x/np.min(x)*t
            
        e_x = np.exp(x)
        
        return e_x / e_x.sum(axis, keepdims=True)

    def train(self, train_imgs,     # the list of images to train the model
                    valid_imgs,     # the list of images used to validate the model
                    train_times,    # the number of time to repeat the training set, often used for small datasets
                    valid_times,    # the number of times to repeat the validation set, often used for small datasets
                    nb_epoch,       # number of epoches
                    learning_rate,  # the learning rate
                    batch_size,     # the size of the batch
                    warmup_epochs,  # number of initial batches to let the model familiarize with the new dataset
                    object_scale,
                    no_object_scale,
                    coord_scale,
                    class_scale,
                    saved_weights_name='best_weights.h5',
                    debug=False):     

        self.batch_size = batch_size
        self.warmup_bs  = warmup_epochs * (train_times*(len(train_imgs)/batch_size+1) + valid_times*(len(valid_imgs)/batch_size+1))

        self.object_scale    = object_scale
        self.no_object_scale = no_object_scale
        self.coord_scale     = coord_scale
        self.class_scale     = class_scale

        self.debug = debug

        if warmup_epochs > 0: nb_epoch = warmup_epochs # if it's warmup stage, don't train more than warmup_epochs

        ############################################
        # Compile the model
        ############################################

        optimizer = Adam(lr=learning_rate, beta_1=0.9, beta_2=0.999, epsilon=1e-08, decay=0.0)
        self.model.compile(loss=self.custom_loss, optimizer=optimizer)

        ############################################
        # Make train and validation generators
        ############################################

        generator_config = {
            'IMAGE_H'         : self.input_size, 
            'IMAGE_W'         : self.input_size,
            'GRID_H'          : self.grid_h,  
            'GRID_W'          : self.grid_w,
            'BOX'             : self.nb_box,
            'LABELS'          : self.labels,
            'CLASS'           : len(self.labels),
            'ANCHORS'         : self.anchors,
            'BATCH_SIZE'      : self.batch_size,
            'TRUE_BOX_BUFFER' : self.max_box_per_image,
        }    

        train_batch = BatchGenerator(train_imgs, 
                                     generator_config, 
                                     norm=self.feature_extractor.normalize)
        valid_batch = BatchGenerator(valid_imgs, 
                                     generator_config, 
                                     norm=self.feature_extractor.normalize,
                                     jitter=False)

        ############################################
        # Make a few callbacks
        ############################################

        early_stop = EarlyStopping(monitor='val_loss', 
                           min_delta=0.001, 
                           patience=3, 
                           mode='min', 
                           verbose=1)
        checkpoint = ModelCheckpoint(saved_weights_name, 
                                     monitor='val_loss', 
                                     verbose=1, 
                                     save_best_only=True, 
                                     mode='min', 
                                     period=1)
        tb_counter  = len([log for log in os.listdir(os.path.expanduser('~/logs/')) if 'yolo' in log]) + 1
        tensorboard = TensorBoard(log_dir=os.path.expanduser('~/logs/') + 'yolo' + '_' + str(tb_counter), 
                                  histogram_freq=0, 
                                  #write_batch_performance=True,
                                  write_graph=True, 
                                  write_images=False)

        ############################################
        # Start the training process
        ############################################        

        self.model.fit_generator(generator        = train_batch, 
                                 steps_per_epoch  = len(train_batch) * train_times, 
                                 epochs           = nb_epoch, 
                                 verbose          = 1,
                                 validation_data  = valid_batch,
                                 validation_steps = len(valid_batch) * valid_times,
                                 callbacks        = [early_stop, checkpoint, tensorboard], 
                                 workers          = 3,
                                 max_queue_size   = 8)