1. 转换前的 .json 格式文件的内容：

json 是一个字典，具体内容看下面这个链接：
https://blog.csdn.net/weixin_42419002/article/details/100159408

2. 转换后的 .xml 格式文件的内容：

<annotation>
	<folder>VOC2012</folder>  #  这些值训练的时候不会被用到
	<filename>2007_000661.jpg</filename>
	<source>
		<database>The VOC2007 Database</database>
		<annotation>PASCAL VOC2007</annotation>
		<image>flickr</image>
	</source>
	<size>
		<width>500</width>  # 这个值需要改变
		<height>375</height>  # 这个值需要改变
		<depth>3</depth>
	</size>
	<segmented>0</segmented>
	<object>
		<name>sofa</name>  # 这个值需要改变
		<pose>Unspecified</pose>
		<truncated>1</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>119</xmin>  # 这个值需要改变
			<ymin>177</ymin>  # 这个值需要改变
			<xmax>331</xmax>  # 这个值需要改变
			<ymax>278</ymax>  # 这个值需要改变
		</bndbox>
	</object>
	<object>
		<name>chair</name>  # 这个值需要改变
		<pose>Unspecified</pose>
		<truncated>1</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>133</xmin>  # 这个值需要改变
			<ymin>159</ymin>  # 这个值需要改变
			<xmax>179</xmax>  # 这个值需要改变
			<ymax>197</ymax>  # 这个值需要改变
		</bndbox>
	</object>
</annotation>

3. 将 .json 转换成 .xml 格式代码：

import  os
import json
from lxml import etree as ET
from xml.dom import minidom

def edit_xml(objects, id, dir):
    save_xml_path = os.path.join(dir, "%s.xml" % id)  # xml

    root = ET.Element("annotation")
    # root.set("version", "1.0")  
    folder = ET.SubElement(root, "folder")
    folder.text = "none"
    filename = ET.SubElement(root, "filename")
    filename.text = "none"
    source = ET.SubElement(root, "source")
    source.text = "201908"
    owner = ET.SubElement(root, "owner")
    owner.text = "YZN"
    size = ET.SubElement(root, "size")
    width = ET.SubElement(size, "width")
    width.text = str(2048)
    height = ET.SubElement(size, "height")
    height.text = str(2048)
    depth = ET.SubElement(size, "depth")
    depth.text = "3"
    segmented = ET.SubElement(root, "segmented")
    segmented.text = "0"
    for obj in objects:  #  
        object = ET.SubElement(root, "object")
        name = ET.SubElement(object, "name")  # number
        name.text = obj["category"]
        # meaning = ET.SubElement(object, "meaning")  # name
        # meaning.text = inf_value[0]
        pose = ET.SubElement(object, "pose")
        pose.text = "Unspecified"
        truncated = ET.SubElement(object, "truncated")
        truncated.text = "0"
        difficult = ET.SubElement(object, "difficult")
        difficult.text = "0"
        bndbox = ET.SubElement(object, "bndbox")
        xmin = ET.SubElement(bndbox, "xmin")
        xmin.text = str(int(obj["bbox"]["xmin"]))
        ymin = ET.SubElement(bndbox, "ymin")
        ymin.text = str(int(obj["bbox"]["ymin"]))
        xmax = ET.SubElement(bndbox, "xmax")
        xmax.text = str(int(obj["bbox"]["xmax"]))
        ymax = ET.SubElement(bndbox, "ymax")
        ymax.text = str(int(obj["bbox"]["ymax"]))
    tree = ET.ElementTree(root)
    tree.write(save_xml_path, encoding="UTF-8", xml_declaration=True)
    root = ET.parse(save_xml_path) 
    file_lines = minidom.parseString(ET.tostring(root, encoding="Utf-8")).toprettyxml(
        indent="\t") 
    file_line = open(save_xml_path, "w", encoding="utf-8")  
    file_line.write(file_lines)
    file_line.close()
    
def  getDirId(dir):  # get the  id list  of id.png
    names = os.listdir(dir)
    ids = []
    for name in names:
        # path = os.path.join(dir, name)
        # img  = cv2.imread(path)
        # w, h, c = img.shape
        # if name.endswith(".jpg") or name.endswith(".png"):
            # ids["%s" % name.split(".")[0]] = [w, h, c]
        ids.append(name.split(".")[0])
    return ids  

filedir = "annotations.json"
annos = json.loads(open(filedir).read())

trainIds =  getDirId("Tinghua100K/images/train/")
testIds =  getDirId("Tinghua100K/images/test/")

ids = annos["imgs"].keys() #  all img ids in .json 

for id in ids:
	#  json 中的ID图片有待检测目标，且该id图片在 train文件夹中
    if len(annos["imgs"][id]["objects"]) > 0 and (id in trainIds) and :
        objects = annos["imgs"][id]["objects"]
        edit_xml(objects, id, dir = "xmlLabel/train")
        
    elif len(annos["imgs"][id]["objects"]) > 0 and (id in testIds):
        objects = annos["imgs"][id]["objects"]
        edit_xml(objects, id, dir = "xmlLabel/test")