目标检测：数据增强

背景

计算机视觉模型训练，使用数据增强防止过拟合是最有效的方法．为了降低标注成本，同时可以有效地扩充数据集（任意比例，数据增强对源数据量也有一定要求，源数据足够多＋数据增强，才能发挥其威力），这里给出一个解决方案

图像数据和标签同时增强方法

源码

import xml.etree.ElementTree as ET
import pickle
import os
from os import getcwd
import numpy as np
from PIL import Image
import shutil
import matplotlib.pyplot as plt

import imgaug as ia
from imgaug import augmenters as iaa


ia.seed(1)


def read_xml_annotation(root, image_id):
    in_file = open(os.path.join(root, image_id))
    tree = ET.parse(in_file)
    root = tree.getroot()
    bndboxlist = []

    for object in root.findall('object'):  # 找到root节点下的所有country节点
        bndbox = object.find('bndbox')  # 子节点下节点rank的值

        xmin = int(bndbox.find('xmin').text)
        xmax = int(bndbox.find('xmax').text)
        ymin = int(bndbox.find('ymin').text)
        ymax = int(bndbox.find('ymax').text)
        # print(xmin,ymin,xmax,ymax)
        bndboxlist.append([xmin, ymin, xmax, ymax])
        # print(bndboxlist)

    bndbox = root.find('object').find('bndbox')
    return bndboxlist


# (506.0000, 330.0000, 528.0000, 348.0000) -> (520.4747, 381.5080, 540.5596, 398.6603)
def change_xml_annotation(root, image_id, new_target):
    new_xmin = new_target[0]
    new_ymin = new_target[1]
    new_xmax = new_target[2]
    new_ymax = new_target[3]

    in_file = open(os.path.join(root, str(image_id) + '.xml'))  # 这里root分别由两个意思
    tree = ET.parse(in_file)
    xmlroot = tree.getroot()
    object = xmlroot.find('object')
    bndbox = object.find('bndbox')
    xmin = bndbox.find('xmin')
    xmin.text = str(new_xmin)
    ymin = bndbox.find('ymin')
    ymin.text = str(new_ymin)
    xmax = bndbox.find('xmax')
    xmax.text = str(new_xmax)
    ymax = bndbox.find('ymax')
    ymax.text = str(new_ymax)
    tree.write(os.path.join(root, str("%06d" % (str(id) + '.xml'))))


def change_xml_list_annotation(root, image_id, new_target, saveroot, id):
    in_file = open(os.path.join(root, str(image_id) + '.xml'))  # 这里root分别由两个意思
    tree = ET.parse(in_file)
    elem = tree.find('filename')
    elem.text = (id + '.jpg')
    xmlroot = tree.getroot()
    index = 0

    for object in xmlroot.findall('object'):  # 找到root节点下的所有country节点
        bndbox = object.find('bndbox')  # 子节点下节点rank的值

        # xmin = int(bndbox.find('xmin').text)
        # xmax = int(bndbox.find('xmax').text)
        # ymin = int(bndbox.find('ymin').text)
        # ymax = int(bndbox.find('ymax').text)

        new_xmin = new_target[index][0]
        new_ymin = new_target[index][1]
        new_xmax = new_target[index][2]
        new_ymax = new_target[index][3]

        xmin = bndbox.find('xmin')
        xmin.text = str(new_xmin)
        ymin = bndbox.find('ymin')
        ymin.text = str(new_ymin)
        xmax = bndbox.find('xmax')
        xmax.text = str(new_xmax)
        ymax = bndbox.find('ymax')
        ymax.text = str(new_ymax)

        index = index + 1

    tree.write(os.path.join(saveroot, id + '.xml'))


def mkdir(path):
    # 去除首位空格
    path = path.strip()
    # 去除尾部 \ 符号
    path = path.rstrip("\\")
    # 判断路径是否存在
    # 存在     True
    # 不存在   False
    isExists = os.path.exists(path)
    # 判断结果
    if not isExists:
        # 如果不存在则创建目录
        # 创建目录操作函数
        os.makedirs(path)
        print(path + ' 创建成功')
        return True
    else:
        # 如果目录存在则不创建，并提示目录已存在
        print(path + ' 目录已存在')
        return False


if __name__ == "__main__":

    IMG_DIR = "../JPEGImages"
    XML_DIR = "../Annotations"

    AUG_XML_DIR = "../xml_aug"  # 存储增强后的XML文件夹路径
    try:
        shutil.rmtree(AUG_XML_DIR)
    except FileNotFoundError as e:
        a = 1
    mkdir(AUG_XML_DIR)

    AUG_IMG_DIR = "../img_aug"  # 存储增强后的影像文件夹路径
    try:
        shutil.rmtree(AUG_IMG_DIR)
    except FileNotFoundError as e:
        a = 1
    mkdir(AUG_IMG_DIR)

    AUGLOOP = 3  # 每张影像增强的数量

    boxes_img_aug_list = []
    new_bndbox = []
    new_bndbox_list = []

    # 影像增强
    seq = iaa.Sequential([
        iaa.Flipud(0.5),  # vertically flip 20% of all images
        iaa.Fliplr(0.5),  # 镜像
        iaa.Multiply((1.2, 1.5)),  # change brightness, doesn't affect BBs
        iaa.GaussianBlur(sigma=(0, 3.0)),  # iaa.GaussianBlur(0.5),
        iaa.Affine(
            translate_px={"x": 15, "y": 15},
            scale=(0.8, 0.95),
            rotate=(-30, 30)
        )  # translate by 40/60px on x/y axis, and scale to 50-70%, affects BBs
    ])

    for root, sub_folders, files in os.walk(XML_DIR):

        for name in files:

            bndbox = read_xml_annotation(XML_DIR, name)
            shutil.copy(os.path.join(XML_DIR, name), AUG_XML_DIR)
            shutil.copy(os.path.join(IMG_DIR, name[:-4] + '.jpg'), AUG_IMG_DIR)

            for epoch in range(AUGLOOP):
                seq_det = seq.to_deterministic()  # 保持坐标和图像同步改变，而不是随机
                # 读取图片
                img = Image.open(os.path.join(IMG_DIR, name[:-4] + '.jpg'))
                # sp = img.size
                img = np.asarray(img)
                # bndbox 坐标增强
                for i in range(len(bndbox)):
                    bbs = ia.BoundingBoxesOnImage([
                        ia.BoundingBox(x1=bndbox[i][0], y1=bndbox[i][1], x2=bndbox[i][2], y2=bndbox[i][3]),
                    ], shape=img.shape)

                    bbs_aug = seq_det.augment_bounding_boxes([bbs])[0]
                    boxes_img_aug_list.append(bbs_aug)

                    # new_bndbox_list:[[x1,y1,x2,y2],...[],[]]
                    n_x1 = int(max(1, min(img.shape[1], bbs_aug.bounding_boxes[0].x1)))
                    n_y1 = int(max(1, min(img.shape[0], bbs_aug.bounding_boxes[0].y1)))
                    n_x2 = int(max(1, min(img.shape[1], bbs_aug.bounding_boxes[0].x2)))
                    n_y2 = int(max(1, min(img.shape[0], bbs_aug.bounding_boxes[0].y2)))
                    if n_x1 == 1 and n_x1 == n_x2:
                        n_x2 += 1
                    if n_y1 == 1 and n_y2 == n_y1:
                        n_y2 += 1
                    if n_x1 >= n_x2 or n_y1 >= n_y2:
                        print('error', name)
                    new_bndbox_list.append([n_x1, n_y1, n_x2, n_y2])
                # 存储变化后的图片
                image_aug = seq_det.augment_images([img])[0]
                path = os.path.join(AUG_IMG_DIR, name[:-4] + '_' + str(epoch+1) + '.jpg')
                #path = os.path.join(AUG_IMG_DIR, str("%06d" % (len(files) + int(name[:-4]) + epoch * 250)) + '.jpg')
                image_auged = bbs.draw_on_image(image_aug, thickness=0)
                Image.fromarray(image_auged).save(path)

                # 存储变化后的XML
                change_xml_list_annotation(XML_DIR, name[:-4], new_bndbox_list, AUG_XML_DIR, name[:-4] + '_' + str(epoch+1) + '.jpg')
                print(name[:-4] + '_' + str(epoch+1) + '.jpg')
                new_bndbox_list = []

需要注意的是源码中使用了imgaug工具包需要先安装, imgaug使用教程：

# 简介

相较于Augmentor，imgaug具有更多的功能，比如对影像增强的同时，对keypoint, bounding box进行相应的变换。例如在目标检测的过程中，训练集包括影像及其对应的bounding box文件，在对影像增强的时候，同时解算出bounding box 相应变换的坐标生成对应的bounding box文件。
# imgaug安装

[imgaug使用文档](https://imgaug.readthedocs.io/en/latest/index.html)
安装依赖库
pip install six numpy scipy matplotlib scikit-image opencv-python imageio
安装imgaug
```python
pip install imgaug

# 使用示例

## 数据准备
输入数据为两个文件夹一个是需要增强的影像数据（JPEGImages），一个是对应的xml文件（Annotations）。**注意：影像文件名需和xml文件名相对应！**

## 设置文件路径
IMG_DIR = "../create-pascal-voc-dataset/examples/VOC2007/JPEGImages"
XML_DIR = "../create-pascal-voc-dataset/examples/VOC2007/Annotations"

AUG_XML_DIR = "./Annotations"  # 存储增强后的XML文件夹路径
AUG_IMG_DIR = "./JPEGImages"  # 存储增强后的影像文件夹路径

## 设置增强次数
AUGLOOP = 10 # 每张影像增强的数量

## 设置增强参数

通过修改Sequential函数参数进行设置，具体设置参考[imgaug使用文档](https://imgaug.readthedocs.io/en/latest/index.html)
seq = iaa.Sequential([
    iaa.Flipud(0.5),  # v翻转
    iaa.Fliplr(0.5),  # 镜像
    iaa.Multiply((1.2, 1.5)),  # 改变明亮度
    iaa.GaussianBlur(sigma=(0, 3.0)),  # 高斯噪声
    iaa.Affine(
        translate_px={"x": 15, "y": 15},
        scale=(0.8, 0.95),
        rotate=(-30, 30)
    )  # translate by 40/60px on x/y axis, and scale to 50-70%, affects BBs
])

## 输出
运行augmentation.py ，运行结束后即可得到增强的影像和对应的xml文件夹