COCO和VOC数据集的转换：VOC2COCO和COCO2VOC

VOC2COCO

方法一

参考自博客
数据格式的转换实际是将VOC的annotation标注文件转化为COCO的json文件
注：下面代码包含通过txt文件生成和通过文件夹生成两种方法
1 通过txt文件生成 ：按照VOC数据集下ImageSets/Main中的已划分好的trian.txt，test.txt，val.txt进行转化，生成对应的3个json文件;
2 通过文件夹生成 ：将annotation文件夹里的xml文件全部转化成一个json文件，一个annotation文件夹转化成一个json文件，要想生成3个trian.json，test.json，val.json文件，需要有3个对应的annotation文件夹（可手动按比例创建3个annotation文件夹，也可写个程序划分annotation文件夹）

import xml.etree.ElementTree as ET
import os
import json
 
coco = dict()
coco['images'] = []
coco['type'] = 'instances'
coco['annotations'] = []
coco['categories'] = []
 
category_set = dict()
image_set = set()
#注意具体应用中，类别索引是从0开始，还是从1开始。
#若从1开始（包含背景的情况）下一句代码需改成category_item_id = 0 
category_item_id = -1
image_id = 20180000000
annotation_id = 0
 
def addCatItem(name):
    global category_item_id
    category_item = dict()
    category_item['supercategory'] = 'none'
    category_item_id += 1
    category_item['id'] = category_item_id
    category_item['name'] = name
    coco['categories'].append(category_item)
    category_set[name] = category_item_id
    return category_item_id
 
def addImgItem(file_name, size):
    global image_id
    if file_name is None:
        raise Exception('Could not find filename tag in xml file.')
    if size['width'] is None:
        raise Exception('Could not find width tag in xml file.')
    if size['height'] is None:
        raise Exception('Could not find height tag in xml file.')
    image_id += 1
    image_item = dict()
    image_item['id'] = image_id
    image_item['file_name'] = file_name
    image_item['width'] = size['width']
    image_item['height'] = size['height']
    coco['images'].append(image_item)
    image_set.add(file_name)
    return image_id
 
def addAnnoItem(object_name, image_id, category_id, bbox):
    global annotation_id
    annotation_item = dict()
    annotation_item['segmentation'] = []
    seg = []
    # bbox[] is x,y,w,h
    # left_top
    seg.append(bbox[0])
    seg.append(bbox[1])
    # left_bottom
    seg.append(bbox[0])
    seg.append(bbox[1] + bbox[3])
    # right_bottom
    seg.append(bbox[0] + bbox[2])
    seg.append(bbox[1] + bbox[3])
    # right_top
    seg.append(bbox[0] + bbox[2])
    seg.append(bbox[1])
 
    annotation_item['segmentation'].append(seg)
 
    annotation_item['area'] = bbox[2] * bbox[3]
    annotation_item['iscrowd'] = 0
    annotation_item['ignore'] = 0
    annotation_item['image_id'] = image_id
    annotation_item['bbox'] = bbox
    annotation_item['category_id'] = category_id
    annotation_id += 1
    annotation_item['id'] = annotation_id
    coco['annotations'].append(annotation_item)
 
def _read_image_ids(image_sets_file):
    ids = []
    with open(image_sets_file) as f:
        for line in f:
            ids.append(line.rstrip())
    return ids
 
"""通过txt文件生成"""
#split ='train' 'va' 'trainval' 'test'
def parseXmlFiles_by_txt(data_dir,json_save_path,split='train'):
    print("hello")
    labelfile=split+".txt"
    image_sets_file = data_dir + "/ImageSets/Main/"+labelfile
    ids=_read_image_ids(image_sets_file)
 
    for _id in ids:
        xml_file=data_dir + f"/Annotations/{_id}.xml"
 
        bndbox = dict()
        size = dict()
        current_image_id = None
        current_category_id = None
        file_name = None
        size['width'] = None
        size['height'] = None
        size['depth'] = None
 
        tree = ET.parse(xml_file)
        root = tree.getroot()
        if root.tag != 'annotation':
            raise Exception('pascal voc xml root element should be annotation, rather than {}'.format(root.tag))
 
        # elem is , , ,