dataloader.py

import math
from random import shuffle

import cv2
import numpy as np
from PIL import Image
from tensorflow import keras
from tensorflow.keras.applications.imagenet_utils import preprocess_input

from utils.utils import cvtColor


class SSDDatasets(keras.utils.Sequence):
    def __init__(self, annotation_lines, input_shape, anchors, batch_size, num_classes, train, overlap_threshold = 0.5):
        self.annotation_lines   = annotation_lines
        self.length             = len(self.annotation_lines)
        
        self.input_shape        = input_shape
        self.anchors            = anchors
        self.num_anchors        = len(anchors)
        self.batch_size         = batch_size
        self.num_classes        = num_classes
        self.train              = train
        self.overlap_threshold  = overlap_threshold

    def __len__(self):
        return math.ceil(len(self.annotation_lines) / float(self.batch_size))

    def __getitem__(self, index):
        image_data  = []
        box_data    = []
        for i in range(index * self.batch_size, (index + 1) * self.batch_size):  
            i = i % self.length
            #---------------------------------------------------#
            #   训练时进行数据的随机增强
            #   验证时不进行数据的随机增强
            #---------------------------------------------------#
            image, box  = self.get_random_data(self.annotation_lines[i], self.input_shape, random = self.train)
            if len(box)!=0:
                boxes               = np.array(box[:,:4] , dtype=np.float32)
                boxes[:, [0, 2]]    = boxes[:,[0, 2]] / self.input_shape[1]
                boxes[:, [1, 3]]    = boxes[:,[1, 3]] / self.input_shape[0]
                one_hot_label   = np.eye(self.num_classes - 1)[np.array(box[:,4], np.int32)]
                box             = np.concatenate([boxes, one_hot_label], axis=-1)
            box = self.assign_boxes(box)

            image_data.append(image)               
            box_data.append(box)
            #print(preprocess_input(np.array(image_data)), np.array(box_data))
            break

        return preprocess_input(np.array(image_data)), np.array(box_data)

    def generate(self):
        i = 0
        while True:
            image_data  = []
            box_data    = []
            for b in range(self.batch_size):
                if i==0:
                    np.random.shuffle(self.annotation_lines)
                #---------------------------------------------------#
                #   训练时进行数据的随机增强
                #   验证时不进行数据的随机增强
                #---------------------------------------------------#
                image, box  = self.get_random_data(self.annotation_lines[i], self.input_shape, random = self.train)
                i           = (i+1) % self.length
                if len(box)!=0:
                    boxes               = np.array(box[:,:4] , dtype=np.float32)
                    boxes[:, [0, 2]]    = boxes[:,[0, 2]] / self.input_shape[1]
                    boxes[:, [1, 3]]    = boxes[:,[1, 3]] / self.input_shape[0]
                    one_hot_label   = np.eye(self.num_classes - 1)[np.array(box[:,4], np.int32)]
                    box             = np.concatenate([boxes, one_hot_label], axis=-1)
                box = self.assign_boxes(box)

                image_data.append(image)               
                box_data.append(box)
            yield preprocess_input(np.array(image_data)), np.array(box_data)

    def rand(self, a=0, b=1):
        return np.random.rand()*(b-a) + a

    def get_random_data(self, annotation_line, input_shape, jitter=.3, hue=.1, sat=1.5, val=1.5, random=True):
        line = annotation_line.split()
        #------------------------------#
        #   读取图像并转换成RGB图像
        #------------------------------#
        image   = Image.open(line[0])
        image   = cvtColor(image)
        #------------------------------#
        #   获得图像的高宽与目标高宽
        #------------------------------#
        iw, ih  = image.size
        h, w    = input_shape
        #------------------------------#
        #   获得预测框
        #------------------------------#
        box     = np.array([np.array(list(map(int,box.split(',')))) for box in line[1:]])

        if not random:
            scale = min(w/iw, h/ih)
            nw = int(iw*scale)
            nh = int(ih*scale)
            dx = (w-nw)//2
            dy = (h-nh)//2

            #---------------------------------#
            #   将图像多余的部分加上灰条
            #---------------------------------#
            image       = image.resize((nw,nh), Image.BICUBIC)
            new_image   = Image.new('RGB', (w,h), (128,128,128))
            new_image.paste(image, (dx, dy))
            image_data  = np.array(new_image, np.float32)

            #---------------------------------#
            #   对真实框进行调整
            #---------------------------------#
            if len(box)>0:
                np.random.shuffle(box)
                box[:, [0,2]] = box[:, [0,2]]*nw/iw + dx
                box[:, [1,3]] = box[:, [1,3]]*nh/ih + dy
                box[:, 0:2][box[:, 0:2]<0] = 0
                box[:, 2][box[:, 2]>w] = w
                box[:, 3][box[:, 3]>h] = h
                box_w = box[:, 2] - box[:, 0]
                box_h = box[:, 3] - box[:, 1]
                box = box[np.logical_and(box_w>1, box_h>1)] # discard invalid box

            return image_data, box
                
        #------------------------------------------#
        #   对图像进行缩放并且进行长和宽的扭曲
        #------------------------------------------#
        new_ar = w/h * self.rand(1-jitter,1+jitter) / self.rand(1-jitter,1+jitter)
        scale = self.rand(.25, 2)
        if new_ar < 1:
            nh = int(scale*h)
            nw = int(nh*new_ar)
        else:
            nw = int(scale*w)
            nh = int(nw/new_ar)
        image = image.resize((nw,nh), Image.BICUBIC)

        #------------------------------------------#
        #   将图像多余的部分加上灰条
        #------------------------------------------#
        dx = int(self.rand(0, w-nw))
        dy = int(self.rand(0, h-nh))
        new_image = Image.new('RGB', (w,h), (128,128,128))
        new_image.paste(image, (dx, dy))
        image = new_image

        #------------------------------------------#
        #   翻转图像
        #------------------------------------------#
        flip = self.rand()<.5
        if flip: image = image.transpose(Image.FLIP_LEFT_RIGHT)

        #------------------------------------------#
        #   色域扭曲
        #------------------------------------------#
        hue = self.rand(-hue, hue)
        sat = self.rand(1, sat) if self.rand()<.5 else 1/self.rand(1, sat)
        val = self.rand(1, val) if self.rand()<.5 else 1/self.rand(1, val)
        x = cv2.cvtColor(np.array(image,np.float32)/255, cv2.COLOR_RGB2HSV)
        x[..., 0] += hue*360
        x[..., 0][x[..., 0]>1] -= 1
        x[..., 0][x[..., 0]<0] += 1
        x[..., 1] *= sat
        x[..., 2] *= val
        x[x[:,:, 0]>360, 0] = 360
        x[:, :, 1:][x[:, :, 1:]>1] = 1
        x[x<0] = 0
        image_data = cv2.cvtColor(x, cv2.COLOR_HSV2RGB)*255 # numpy array, 0 to 1

        #---------------------------------#
        #   对真实框进行调整
        #---------------------------------#
        if len(box)>0:
            np.random.shuffle(box)
            box[:, [0,2]] = box[:, [0,2]]*nw/iw + dx
            box[:, [1,3]] = box[:, [1,3]]*nh/ih + dy
            if flip: box[:, [0,2]] = w - box[:, [2,0]]
            box[:, 0:2][box[:, 0:2]<0] = 0
            box[:, 2][box[:, 2]>w] = w
            box[:, 3][box[:, 3]>h] = h
            box_w = box[:, 2] - box[:, 0]
            box_h = box[:, 3] - box[:, 1]
            box = box[np.logical_and(box_w>1, box_h>1)] 
        
        return image_data, box

    def on_epoch_begin(self):
        shuffle(self.annotation_lines)

    def iou(self, box):
        #---------------------------------------------#
        #   计算出每个真实框与所有的先验框的iou
        #   判断真实框与先验框的重合情况
        #---------------------------------------------#
        inter_upleft    = np.maximum(self.anchors[:, :2], box[:2])
        inter_botright  = np.minimum(self.anchors[:, 2:4], box[2:])

        inter_wh    = inter_botright - inter_upleft
        inter_wh    = np.maximum(inter_wh, 0)
        inter       = inter_wh[:, 0] * inter_wh[:, 1]
        #---------------------------------------------# 
        #   真实框的面积
        #---------------------------------------------#
        area_true = (box[2] - box[0]) * (box[3] - box[1])
        #---------------------------------------------#
        #   先验框的面积
        #---------------------------------------------#
        area_gt = (self.anchors[:, 2] - self.anchors[:, 0])*(self.anchors[:, 3] - self.anchors[:, 1])
        #---------------------------------------------#
        #   计算iou
        #---------------------------------------------#
        union = area_true + area_gt - inter

        iou = inter / union
        return iou

    def encode_box(self, box, return_iou=True, variances = [0.1, 0.1, 0.2, 0.2]):
        #---------------------------------------------#
        #   计算当前真实框和先验框的重合情况
        #   iou [self.num_anchors]
        #   encoded_box [self.num_anchors, 5]
        #---------------------------------------------#
        iou = self.iou(box)
        encoded_box = np.zeros((self.num_anchors, 4 + return_iou))
        
        #---------------------------------------------#
        #   找到每一个真实框，重合程度较高的先验框
        #   真实框可以由这个先验框来负责预测
        #---------------------------------------------#
        assign_mask = iou > self.overlap_threshold

        #---------------------------------------------#
        #   如果没有一个先验框重合度大于self.overlap_threshold
        #   则选择重合度最大的为正样本
        #---------------------------------------------#
        if not assign_mask.any():
            assign_mask[iou.argmax()] = True
        
        #---------------------------------------------#
        #   利用iou进行赋值 
        #---------------------------------------------#
        if return_iou:
            encoded_box[:, -1][assign_mask] = iou[assign_mask]
        
        #---------------------------------------------#
        #   找到对应的先验框
        #---------------------------------------------#
        assigned_anchors = self.anchors[assign_mask]

        #---------------------------------------------#
        #   逆向编码，将真实框转化为ssd预测结果的格式
        #   先计算真实框的中心与长宽
        #---------------------------------------------#
        box_center  = 0.5 * (box[:2] + box[2:])
        box_wh      = box[2:] - box[:2]
        #---------------------------------------------#
        #   再计算重合度较高的先验框的中心与长宽
        #---------------------------------------------#
        assigned_anchors_center = (assigned_anchors[:, 0:2] + assigned_anchors[:, 2:4]) * 0.5
        assigned_anchors_wh     = (assigned_anchors[:, 2:4] - assigned_anchors[:, 0:2])
        
        #------------------------------------------------#
        #   逆向求取ssd应该有的预测结果
        #   先求取中心的预测结果，再求取宽高的预测结果
        #   存在改变数量级的参数，默认为[0.1,0.1,0.2,0.2]
        #------------------------------------------------#
        encoded_box[:, :2][assign_mask] = box_center - assigned_anchors_center
        encoded_box[:, :2][assign_mask] /= assigned_anchors_wh
        encoded_box[:, :2][assign_mask] /= np.array(variances)[:2]

        encoded_box[:, 2:4][assign_mask] = np.log(box_wh / assigned_anchors_wh)
        encoded_box[:, 2:4][assign_mask] /= np.array(variances)[2:4]
        return encoded_box.ravel()

    def assign_boxes(self, boxes):
        #---------------------------------------------------#
        #   assignment分为3个部分
        #   :4      的内容为网络应该有的回归预测结果
        #   4:-1    的内容为先验框所对应的种类，默认为背景
        #   -1      的内容为当前先验框是否包含目标
        #---------------------------------------------------#
        assignment          = np.zeros((self.num_anchors, 4 + self.num_classes + 1))
        assignment[:, 4]    = 1.0
        if len(boxes) == 0:
            return assignment

        # 对每一个真实框都进行iou计算
        encoded_boxes   = np.apply_along_axis(self.encode_box, 1, boxes[:, :4])
        #---------------------------------------------------#
        #   在reshape后，获得的encoded_boxes的shape为：
        #   [num_true_box, num_anchors, 4 + 1]
        #   4是编码后的结果，1为iou
        #---------------------------------------------------#
        encoded_boxes   = encoded_boxes.reshape(-1, self.num_anchors, 5)
        
        #---------------------------------------------------#
        #   [num_anchors]求取每一个先验框重合度最大的真实框
        #---------------------------------------------------#
        best_iou        = encoded_boxes[:, :, -1].max(axis=0)
        best_iou_idx    = encoded_boxes[:, :, -1].argmax(axis=0)
        best_iou_mask   = best_iou > 0
        best_iou_idx    = best_iou_idx[best_iou_mask]
        
        #---------------------------------------------------#
        #   计算一共有多少先验框满足需求
        #---------------------------------------------------#
        assign_num      = len(best_iou_idx)

        # 将编码后的真实框取出
        encoded_boxes   = encoded_boxes[:, best_iou_mask, :]
        #---------------------------------------------------#
        #   编码后的真实框的赋值
        #---------------------------------------------------#
        assignment[:, :4][best_iou_mask] = encoded_boxes[best_iou_idx,np.arange(assign_num),:4]
        #----------------------------------------------------------#
        #   4代表为背景的概率，设定为0，因为这些先验框有对应的物体
        #----------------------------------------------------------#
        assignment[:, 4][best_iou_mask]     = 0
        assignment[:, 5:-1][best_iou_mask]  = boxes[best_iou_idx, 4:]
        #----------------------------------------------------------#
        #   -1表示先验框是否有对应的物体
        #----------------------------------------------------------#
        assignment[:, -1][best_iou_mask]    = 1
        # 通过assign_boxes我们就获得了，输入进来的这张图片，应该有的预测结果是什么样子的
        return assignment